Table of contents

Following the success of the 1st International Symposium on Functional Materials held in Kuala Lumpur, Malaysia, 5–8 December 2005, the second symposium was held in the beautiful city of Hangzhou, People's Republic of China, 16–19 May 2007. The latter symposium was a gathering of about 200 renowned researchers from 16 countries around the world. The conference consisted of 24 symposia, 5 keynote papers, 21 invited papers, 108 oral presentations and about 160 poster papers covering the frontier areas of materials science and technology of functional materials. They included topics such as energy storage materials, ferroelectric materials, ferromagnetic materials, ferroelectric thin films, applications of functional materials, nanofabrication, computational design, shape memory alloys, application of shape memory materials, ferroelectrics and thermoelectrics, advances in characterizations, magneto-optical materials, Zn and Ti oxides, synthesis of nanopowders and wires, and many other advanced functional materials. With the receipt of more than 396 abstracts, this conference was a gathering of great minds in one place to discuss the research frontiers and discoveries in functional materials.

The Organizing Committee would like to express its sincere thanks to the members of the International Advisory Committee for their invaluable contributions to the symposium. The committee is also grateful for the generous support from the many sponsors. A word of sincere thanks needs to go to Professor Roger Wäppling, Editor-in-Chief and the editorial staff of IOP Publishing for the publication of selected papers in this special issue of Physica Scripta. Finally, our deepest gratitude should be directed to the National University of Singapore, Zhejiang University and the General Research Institute for Nonferrous Metals, People's Republic of China for, without their support, the conference would not have been a success.

The full text of this introduction is available in the PDF.

An overview of the development of magnetic materials from early natural magnets to the advanced materials prepared, characterized and, in many cases, used in today's society will be given.

Pyroelectric infra-red detector arrays provide an attractive solution to the problem of collecting spatial information in the far IR. They are only sensitive to changes in the IR flux and are well suited to sensing movements of people. The applications of low cost arrays with limited (a few hundred) elements for people sensing and radiometry will be illustrated. The performances of uncooled pyroelectric arrays are ultimately driven by the materials used. For this reason, continuous improvements in materials technology and figures-of-merit (FoM) are important. The performance of dense, bulk pyroelectric ceramics has not increased for several years, but nevertheless it is possible to obtain significant improvements in performance through the use of tape-cast, functionally gradient materials (FGMs) in which controlled porosity is used to control the permittivity and heat capacity of the material. A model for the performance of such a material will be presented, and compared with experimentally determined properties of FGMs based on a modified-PZT pyroelectric ceramic. The use of ferroelectric thin films is offering considerable potential for low cost and high performance. It will be shown that the introduction of controlled amounts of porosity can have a significant positive effect on the relevant pyroelectric FoM.

Ferroelectric Pb[Zr_0.4Ti_0.6]O₃ ceramics codoped with La³⁺ and Fe³⁺ at dopant concentrations of 1.0 and 0.5 mol. %, respectively, were investigated by means of multifrequency electron paramagnetic resonance (EPR) spectroscopy. The results prove that iron is incorporated at the [Zr,Ti]-site, acts as an acceptor and favors the creation of charged (Fe ' _{Zr, Ti}- V_O^••)^• defect dipoles that may give rise to internal bias fields also for 'soft' piezoelectric compounds. In particular, the iron functional center site symmetry was investigated. A multi-site situation was observed in which the orientation of the (Fe ' _{Zr, Ti}- V_O^••)^• defect dipole with respect to the orientation of spontaneous polarization is responsible for a (Fe ' _{Zr, Ti}- V_O^••)^• center of 'tetragonal' and a different center of 'rhombic' local site symmetry.

Carbon nanotubes (CNTs) have been synthesized through chemical vapor deposition in argon gas atmosphere using Fe–2.5%Mo alloyed nanoparticles as a catalyst and H₂/CH₄ gas mixture as a reaction gas. Fe–2.5 wt.%Mo alloyed nanoparticles with average diameter of 7, 20, 45 and 85 nm are prepared by the chemical vapor condensation process using the pyrolysis of iron pentacarbonyl (Fe(CO)₅) and molybdenum hexacarbonyl (Mo(CO)₆). The morphologies of the CNTs are controlled by adjusting the nanoparticle size, reaction gas ratio and reaction temperature. With decreasing nanoparticle size under the same experimental conditions, the degree of crystalline perfection increases gradually and the morphologies of the carbon nanotubes vary from multi wall carbon nanotubes to single wall carbon nanotubes. Also, the ratio of reaction gas has an effect on the morphology and the degree of crystallinity of CNTs. In this work, it is suggested that morphology, diameter and degree of crystallinity of CNTs could be controlled by adjusting the reaction gas ratio, reaction temperature and catalyst size.

TiO₂, ZrO₂ and HfO₂ thin films have been deposited selectively using metal-organic chemical vapour deposition (MOCVD) technique with various single molecular precursors on Si(100) substrates which were patterned with octadecyltrichlorosilane (OTS) applied by microcontact printing (μ CP). Titanium (IV) isopropoxide [Ti(OⁱPr)₄], bis-isopropoxy-bis-tertiarybutyl- acetoacetate zirconium [Zr(Oⁱ Pr)₂ (tbaoac)₂ ] and hafnium tert-butoxide [Hf(O^tBu)₄ ] were used for titanium dioxide (TiO₂), hafnium and zirconium oxide (ZrO₂ and HfO₂) thin films, respectively. Selective depositions were successfully carried out in a home-made MOCVD system. All the deposited thin films had higher reactivity on bare silicon surfaces than OTS self-assembled monolayers (SAMs) deposited area. However, there was slightly different selective growth tendency on OTS deposited Si(100) surfaces. The selectivity tendency of the deposited thin films was revealed in order of TiO₂, HfO₂ and ZrO₂. This tendency was explained by means of film growth rate, structures and molecular weight of precursors and acidity of transition metal of precursors.

GaSb epilayers grown on GaAs(001) vicinal substrate misoriented towards (111) plane were studied using high-resolution x-ray diffraction (HRXRD). The results show that GaSb epilayers exhibit positive crystallographic tilt and the distribution of 60° misfit dislocations (MDs) is imbalanced. The vicinal substrate also leads to the anisotropy of the mosaic structure, i.e. the lateral coherent lengths in directions are larger than those in [110] directions. Furthermore, the full-width at half maximum (FWHM) of the off-axis peaks varies with the inclination angle, which is a result of different dislocation densities in the glide planes.

Well-crystalline LiFePO₄ nanoparticles were prepared by the polyol process without post heat treatments. X-ray diffraction showed an orthorhombic phase without any discernible existence of impurities. The particles showed highly crystalline nature of rod and plate like morphologies with an average size of 300 nm. The initial discharge curve of LiFePO₄ showed a capacity of 168 mAh g⁻¹ at a 0.1 C rate in the voltage range of 2.5–4 V with good retention at high rate current densities. This amounts to a utilization efficiency of 98%, with excellent reversibility in extended cycles. LiFePO₄ nano-particle showed a high capacity of 102 mAh g⁻¹ at a high rate of 6.4 C.

Surface nano-structuring on photoresist beyond the diffraction limit has been investigated by using total internal reflection induced evanescence wave interference with a Lloyd's mirror. The size of the patterns can be down to 80 nm with the incident laser wavelength, λ, of 325 nm, less than λ/4 resolution. This may be attributed to laser induced evanescent wave, which has a shorter wavelength than that of the incident laser in air. The energy distribution of evanescent wave interference patterns was studied theoretically. It shows good agreement with the experiments. This technique can be used to improve traditional laser interference lithography to get smaller feature sizes with a simple modification by putting a prism in front of the sample only.

In this work, HT-LiCoO₂ films with preferential c-axis orientation were prepared using pulsed laser deposition. The kinetics of lithium ion transport through the HT-LiCoO₂ film was investigated by applying potentiostatic intermittent titration technique (PITT). The capacity retention capability of the HT-LiCoO₂ film was studied using constant-current (CC) cycling. PITT measurement showed that the lithium chemical diffusion coefficient () of the HT-LiCoO₂ films reached as high as 10⁻⁸–10⁻¹⁰ cm² s⁻¹ and the value of in the two-phase coexistence region was lower than that in other single-phase regions. CC cycling revealed that the HT-LiCoO₂ film delivered an initial discharge capacity of 40 μAh μm⁻¹ cm⁻² and the discharge capacity decreased to 22.4 μAh μm⁻¹ cm⁻² after 100 CC cycles. The observation was found to be caused by the continuous formation of the spinel phase (LiCo₂O₄ or Co₃O₄).

Spinel LiNi_0.5Mn_1.5O₄ thin film electrodes of 0.5 μm thickness were prepared on polished stainless steel (SS) substrates by pulsed laser deposition. Kinetics and mass-transport of Li intercalation/deintercalation were investigated by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and potentiostatic intermittent titration technique (PITT). The CV measurements indicate that there exists a small amount of Mn^{3 +} in the film and Li transportation is controlled by diffusion at high scan rates. EIS measurements show a potential independent low charge-transfer resistance region between 4.1 and 4.7 V and a stable surface layer resistance through the full potential range. The chemical diffusion coefficients of Li in the LiNi_0.5Mn_1.5O₄ thin film obtained by EIS and PITT have been found to be in the range of 10⁻¹²–10⁻¹⁰ cm² s⁻¹ depending on the electrode potential. Two minima were found for from PITT at potentials close to the peak potentials of the corresponding CV.

Layer-structured LiMn_0.9Co_0.1O₂ cathode materials for lithium-ion batteries were synthesized by ion exchange method. A layer of LiCoO₂ was coated on the surface of the as-prepared LiMn_0.9Co_0.1O₂ powder via melting impregnation method. The structure and morphology of the powders were characterized by means of x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical properties of the cathode materials were investigated using a half-cell in a potential range of 2.0–4.5 V versus Li/Li⁺. The LiMn_0.9Co_0.1O₂ coated with 7 wt.% of LiCoO₂ exhibited good electrochemical properties with a discharge capacity of 158 mAh g⁻¹ and 89% charge retention after 50 cycles.

A rotary evaporation process was applied to improve electrical contact between acetylene black (AB) and Si electrode. Morphologies and electrochemical properties of the Si electrode were compared with those of conventionally prepared Si electrode. In the evaporated Si electrode, AB particles consisted of network-like structure surrounding the surface of Si particle, while in the conventional one, AB particles partially stuck on the Si surface. Increasing the current density from 0.1 to 0.5 C, stable cycle behavior with a slight decrease in discharge capacity was found in the evaporated electrode, while unstable cycle behavior with a significantly decreased capacity was observed in the conventional electrode. At high-current density (0.5 C rate), the discharge capacity of the evaporated Si electrode was maintained over 480 mAh g⁻¹ after 100 cycles. The good cycle performance was attributed to the low resistance induced by the improved interfacial contact between AB and Si particles.

The manganese and chromium oxide nanocomposite electrode materials were synthesized by redox reactions using transition metal powders in solutions. The layered Li[Cr_xLi_{(1/3 − x/3)}Mn_{(2/3 − 2x/3)}] O₂ (x= 0.054, 0.0142, 0.147 and 0.311) materials having α-NaFeO₂ (R-3 m) structure were prepared by solid-state reactions with LiOH and the pre-prepared manganese and chromium precursors. The amount of chromium, after removing the traces of Li₂CrO₄ from the prepared samples, is found to increase with temperature. The Li[Cr_xLi_{(1/3 − x/3)}Mn_{(2/3 − 2x/3)}] O₂ material with x = 0.147 exhibits a high discharge capacity of 280 mAh g^{− 1} in the first cycle and a good reversible capacity of about 250 mAh g^{− 1} when cycled in the voltage range 2.0–4.9 V. Whereas, the Li[Cr_xLi_{(1/3 − x/3)}Mn_{(2/3 − 2x/3)}]O₂ material with x = 0.311 delivers a very low initial discharge capacity of 98 mAh g⁻¹, which is found to be increased up to a discharge capacity of about 260 mAh g^{− 1} at the 30th cycling. This drastic increase in capacity is attributed to the redox couples of Cr^{+ 4/}Cr^{+ 6} and Cr^+3/Cr⁺⁴.

To prevent the dissolution of lithium polysulfides into liquid electrolyte and to promote the lithium/sulfur redox reaction, nano-sized Al₂O₃ particles having large specific surface area were added into sulfur electrode. The effects of nano-sized Al₂O₃ particles on the electrochemical properties of sulfur electrode for lithium/sulfur battery were investigated using CV measurements, charge/discharge tests and ionic conductivity measurements of liquid electrolyte. From the results, the sulfur electrode containing nano Al₂O₃ particles showed good cycle performance and higher discharge capacity of 660 mAh g⁻¹-sulfur than that of the sulfur electrode without nano Al₂O₃. It is therefore concluded that the addition of nano-sized Al₂O₃ particles gives the beneficial effects of preventing the dissolution of lithium polysulfides into liquid electrolyte.

Carbon-coated lithium iron phosphate (LiFePO₄/C) cathode material was synthesized by mechano-chemical activation method. The performance of LiFePO₄/C in lithium battery was tested with an electrospun polymer-based electrolyte. Liquid electrolyte of 1M lithium hexafluorophosphate (LiPF₆) in ethylene carbonate/dimethyl carbonate (EC/DMC) (1 : 1vol) was incorporated in electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-HFP)) microfibrous membrane to prepare the polymer electrolyte (PE). The cell based on Li|PE|Li FePO₄/C exhibited an initial discharge capacity of 142 mAh g⁻¹ at 0.1 C-rate at room temperature. Good cycling performance even under the high current density of 2 C could be obtained. Impedance spectroscopy was applied to investigate the material behavior during 0.1 C-rate charge–discharge cycling. When the fresh cell and the cell after different cycles were compared, impedance resistance was found to decrease with cycling. Impedance study indicated good cycle life for the cell when tested at room temperature.

Three kinds of electrolytes are investigated to find out the proper electrolyte for magnesium battery. Propylene carbonate electrolyte using magnesium salt of Mg(ClO₄)₂ shows a higher ionic conductivity than that of dimethyl carbonate and tri(ethyleneglycol dimethyl)ether (TRGDME) but low decomposition potential. The TRGDME electrolyte with 0.5 M Mg(ClO₄)₂ has a higher ionic conductivity of 6 × 10⁻⁴  S cm⁻¹ than that of dimethyl carbonate, but the decomposition voltage of the electrolyte is over 3.0 V which can be used for Mg/S cell.

LiMn₂O₄ spinel thin films were deposited by radio frequency (rf) magnetron sputtering followed by annealing at 600 °C in air.The films were then post-treated with an rf driven oxygen plasma. The crystallization and surface morphology of LiMn₂O₄ thin films were seen to change with rf power. The treated samples were tested under harsh conditions such as deep discharge to 1.5 V and cycling at elevated temperature of 60 °C to verify the electrochemical performances of LiMn₂O₄ cathodes. The oxygen plasma treatments improved the electrochemical properties of LiMn₂O₄ thin films significantly. As the cells were cycled in the range of 4.5–2.0 V at 60 °C, the samples treated at a proper rf power of 50 W exhibited an initial capacity greater than ∼400 mAh g⁻¹ with reasonable cycling stability. The results were attributed to the change of morphology and the formation of a surface layer induced by the oxygen plasma irradiation.

Carbon nanofibers (CNFs) were grown directly on activated carbon fiber fabric (ACFF), which was then used as the electrode of supercapacitors. Cyclic voltammetry and ac impedance were used to characterize the electrochemical properties of ACFF and CNF/ACFF electrodes in both aqueous and organic electrolytes. ACFF electrodes show higher specific capacitance than CNF/ACFF electrodes due to larger specific surface area. However, the spaces formed between the CNFs in the CNF/ACFF electrodes are more easily accessed than the slit-type pores of ACFF, and much higher electrical-double layer capacitance was obtained for CNF/ACFF electrodes.

Ni sulfides were formed on a Ni-deposited Ti–50.0Ni(at) alloy by annealing under a sulfur pressure of 100 kPa at 673 K for 0.36 ks. Martensitic transformation, superelasticity and electrochemical properties were characterized using different techniques. Ni sulfides consisting of NiS and NiS₂ of thickness 0.8 μ m were formed by a reaction between Ni and S. Some spherical particles and pores were found in the sulfides. A Ti–50.0Ni alloy with Ni sulfide surface layers showed a two-stage B2–R–B19' transformation behavior. A partial superelasticity with a superelastic recovery ratio of 78% found in a current collector showed a clear discharge behavior with a voltage plateau between 1.3–1.6 V. Discharge capacities of the Ni sulfide cathode decreased largely from 700 to 510  mAh(g-NiS₂)⁻¹ with increasing number of cycles up to 3, above which it decreased gradually.

Cr-doped InNbO₄ powder was synthesized using a solid-state reaction and then loaded with 1.0 wt.% NiO on the particle surface. The powder was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectrometry. The (In_0.9Cr_0.1)NbO₄ : NiO showed a novel photocatalysis performance with obvious absorption in the visible light region. The Mm (Ni_3.6Mn_0.4Al_0.3Co_0.7)/(In_0.9Cr_0.1)NbO₄ :NiO photoelectrode was then fabricated and its photo-assisted electrochemical behaviour was investigated. The electrode exhibited the obvious photo-assisted chargeable properties in KOH solution. The high photocatalysed activity may result from the increase in visible light absorption induced by Cr^{3 +} doping and the higher degree of charge carrier separation induced by NiO particles loading on the Cr-InNbO₄ particle surface.

The NaAlH₄ complex is attracting great attention for its potential applications in hydrogen-powered fuel-cell vehicles due to its high hydrogen storage capacity and suitable thermodynamic properties. However, its practicable hydrogen storage capacity presently obtained is less than the theoretical capacity (5.6 wt.%). To improve the hydrogen capacity, we chose metallic Ti or/and Zr powder as catalyst dopants, and prepared the sodium aluminum hydride by hydrogenation of ball-milled NaH/Al mixture containing 10 mol% dopants with different proportions of Ti and Zr, and then investigated the effects on their hydrogen storage (dehydriding) properties. The results showed that different catalyst dopants affected the dehydriding properties greatly. The catalysis of metal Ti as a catalyst dopant alone on dehydriding kinetics for the entire dehydrogenation process of ball-milled (NaH/Al) composite was higher than that of adopting Zr alone. The synergistic catalytic effect of Ti and Zr together as co-dopants on the dehydrogenation process of (NaH/Al) composite was higher than that using only Ti or Zr as dopant individually. The composite doped with proper proportion of Ti and Zr together (8 mol% Ti+ 2 mol% Zr) as co-dopants exhibited the highest dehydriding kinetic property and desorption capacity.

The effects of Ni powder, a conductive material, on the electrochemical properties of Ti_0.8Zr_0.2V_2.7Mn_0.5Cr_0.8Ni_1.25 alloy electrodes were investigated. The maximum discharge capacity of the alloy electrodes is increased from 222.4 to 347.9 mAh g⁻¹ by increasing the weight ratio of Ni powder to Ti_0.8Zr_0.2V_2.7Mn_0.5Cr_0.8Ni_1.25 alloy powder from 0 to 4. The cycling stability and the high rate dischargeability show a gradually increasing tendency with increasing weight ratio of the Ni powder in the electrodes. In addition, the electrochemical kinetic properties of the alloy electrodes have also been improved when the weight ratio of Ni powder in the electrodes is increased.

The stability of engineered domains in LiNbO₃ (LN) and LiTaO₃ (LT) both in near-stoichiometric and congruent composition was investigated using scanning probe microscopy (SPM). Subsequent piezoresponse images showed that the stability of the domains engineered in LN and LT were strongly related to the nonstoichiometric defects in the crystals. In the near-stoichiometric LN, the shape of the linear domains engineered at an angle to the crystallographic Y-axis changed due to wall movements during SPM scanning. However, in the congruent LN, there was no change in the shape of the linear domains. In the near-stoichiometric LT (SLT), backswitching was observed in the engineered domains induced by the heat treatment and that the wall movements corresponding to the back-switching depended on the domain structure and heating temperature. No backswitching was observed in the congruent LT after the same heat treatment. The thermal stability of engineered domains in the near-SLT could be characterized by the effects of domain wall energy and surface electrostatic energy.

Static and dynamic domain behavior of ferroelectric fluoride BaMgF₄ single crystal was investigated using high-resolution piezoresponse force microscopy. High domain wall anisotropy was found in the as-grown BaMgF₄ crystal. Antiparallel domain wall strain phenomena due to defects across the domain boundary were directly observed. The lateral domain growth in the inhomogeneous AFM tip field revealed the activation mechanism of the domain wall motion.

A 2D phononic crystal (PC) with a sandwich type of heterostructure is proposed by replacing two columns of circular scatter cylinders with two columns of square scatter cylinders. The sonic waveguide characteristics of the structure are calculated from f_d= 0 to f_d =0.5 by combining the plane-wave expansion method and a supercell technique. The results show that there are defect bands when -45°<θ<45°, f=0.7 and f_d = 0.5. The number and position of defect bands change with θ and are symmetric to the direction of (0, 1). For the situation that f= 0.7 and the projection of the diagonal of the square scatter cylinder in the direction of (1, 0) is smaller than 2.118 R, there are defect bands and the number of bands decreases with the increase of f_d. The sonic waveguide characteristics of the PC would not change with the orientation and the type of cross-section of the defect cylinders when f_d is very small.

Preparation, microstructure and thermoelectric properties of the bulk (AgSbTe₂)_m (PbTe)_n family of compounds AgPb₁₈Sb_1−xTe₂₀ with x = 0.1, 0.3 and 0.5 have been studied. More homogeneous samples with the absence of nanosized inhomogeneity were obtained by quenching the melts in liquid nitrogen. The Seebeck coefficients of AgPb₁₈Sb_1−xTe₂₀ were negative, indicating n-type conduction behavior. The highest power factor of PF = 0.25 × 10⁻³ W m⁻¹ K⁻² is found for the sample AgPb₁₈Sb_0.9Te₂₀ at 470 K. The influence of Sb content in the AgPb₁₈Sb_1−xTe₂₀ compounds was also investigated. The results suggested that the preparation conditions, microstructure and compositions strongly affect the thermoelectric properties of this series of compounds.

Nanostructured Bi₂Te₃ compounds have been synthesized by a circulating reflux method. The morphologies of the nanopowders are mainly related to the surfactants and reactants used in the syntheses. Bi₂Te₃ nanocomposites were obtained by hot-pressing the mixture of nano and micro-powders of Bi₂Te₃ in different ratios. It is found that the electrical transport properties of the nanocomposites are different from conventional Bi₂Te₃ alloys. Electrical conductivity increased while the Seebeck coefficient changed from positive to negative with increasing temperature.

Mg₂Si_1−xSn_x (x = 0.2, 0.4, 0.6 and 0.8) thermoelectric materials have been prepared by vacuum melting and melting/hot-pressing methods. The phase structures and electrical transport properties were measured. The relationships between electronic structures and electronic properties are discussed. X-ray diffraction (XRD) showed that the hot-pressed compounds were better formed. The electrical conductivity and Seebeck coefficient measurements showed that the properties of the compounds were dramatically affected by solid solubility. When x= 0.2, the highest electrical conductivity resulted in the highest power factor of 1.32×10⁻³ W m⁻¹ K⁻² at about 500 K, while the highest value of Seebeck coefficient of −459 μV K⁻¹ was obtained at about 450 K for x= 0.6.

Pr-lean and boron enriched Pr₉Fe_bal.Co_xTi_yB_11−zC_z (x=0, 10; y=0, 2.5 and 4; z=0–11) alloys have been employed in melt spinning to develop high coercivity and high magnetic energy product nanocomposite ribbons. Increase in C substitution in Co-free Pr₉Fe_bal.Ti_2.5B_11−zC_z (z=0–11) ribbons degrades B_r, _iH_c and (BH)_max monotonically. However, in higher Ti content Pr₉Fe_bal.Ti₄B_11−zC_z ribbons, a slight substitution of C for B (z=0.5–1) is beneficial in simultaneously improving the coercivity and magnetic energy product. Further substitution of 10 at.% Co for Fe may improve not only the magnetic properties but also the temperature coefficient of remanence and the temperature coefficient of coercivity, which are mainly the results of the enhanced magnetization of both magnetically soft and hard phases and the refined microstructure. Optimum magnetic properties of B_r=10.0 kG, _iH_c =10.5 kOe, (BH)_max =20.2 MGOe and α =−0.092% °C⁻¹, β =−0.504% °C⁻¹ could be achieved in Pr₉Fe₆₆Co₁₀Ti₄B₁₀C₁ ribbons.

In this study, CoNiFe/Cu composite wires were deposited using electroplating. The deposited material composition was controlled by adjusting the concentration of Co ions. The results showed that the surface morphology and particle size did not change much with different compositions. However, the coercivity of the composite wires varied significantly for different compositions. A magnetic layer, with the composition of Co₃₀Ni₅₀Fe₂₀, was found to possess a low coercivity value of 0.65 Oe. This is due to the low magneto-strictive factor for the alloy with this composition. In addition, the results showed that the concentration of Fe ions played an important role in achieving low coercivity and high magneto-impedance (MI) effect in the CoNiFe/Cu wires.

Ferroelectric and ferromagnetic materials have wide engineering applications. The defects and size effects are important reliability and sensitivity issues in the application of such materials. In this paper, phase field simulations were carried out to study the effects of cracks in ferroelectrics and size effects on ferromagnetics. In the former simulation, the crack tip domain switching regions and stress fields were plotted. The results obtained showed that a negative electric field tends to open the crack, whereas a positive field tends to close it. In the latter simulation, it was found that both the hysteresis and coercivity were greatly affected by the ratio of the characteristic length to domain wall width.

The exchange coupled composite (ECC) media consisting of a magnetically hard CoCrPt–SiO₂ layer and a magnetically soft FeCoTaCr layer were fabricated as an approach to improve writability. A nonmagnetic CoCr layer with different thickness was inserted between the hard and soft layers to adjust the exchange coupling strength. With proper CoCr thickness, a decrease of coercivity was observed. Transmission electron microscopy (TEM) revealed that the soft/hard stacked grains were magnetically isolated by SiO₂ along grain boundaries. Magnetic properties were characterized by vibrating sample magnetometer (VSM). Angle-dependent coercivity indicated that the stacked magnetic grains switched magnetically in a coherent mode. Angle-dependent switching field demonstrated that ECC media had a better tolerance of the angle dispersion than perpendicular media. The switching field decreased with the increase in thickness of the soft magnetic layer. However, the thermal stability factor was kept almost constant (150) until the soft layer was over 3.3 nm.

The new half-metal TiFe₂O₄ is designed and optimized based on first-principle pseudo-potentials. The electronic and magnetic properties including the spin-polarized energy band structures and state densities, the charges, and the molecular magnetic moments of TiFe₂O₄ are calculated and compared with those of Fe₃O₄. It is found that TiFe₂O₄ is a new ferromagnetic II-B half-metal, which is different from ferrimagnetic Fe₃O₄. The conductivity of TiFe₂O₄ is a little higher than that of TiFe₂O₄. The molecular magnetic moment of 6.68μ_B of TiFe₂O₄ is remarkably higher than 4.0μ_B of Fe₃O₄. Doping of Ti-atoms into Fe₃O₄ is helpful in improving the room temperature magnetoresistance. Localization of Fe 3d or Ti 3d electrons caused by hybridization of O 2p and Fe 3d or Ti 3d orbits is the mechanism by which TiFe₂O₄ has higher molecular magnetic moment and conductivity, and hence higher room magnetoresistance.

Li⁺-doped zinc oxide (ZnO) piezoelectric thin films with preferred c-axis orientation along (002) were fabricated by the sol–gel method. The doping sources of Li⁺ were LiCl, Li₂ CO₃ and their mixtures (LiCl + Li₂ CO₃). Effects of the three doping sources and annealing temperature on the characteristics of preferred c-axis orientation degree and resistivity of ZnO films were investigated. It was found that the annealing temperature at which the ZnO film had good preferred c-axis orientation decreased from 600 to 550 ^° C. The increase in ZnO resistivity by doping LiCl was larger than that by doping Li₂ CO₃. The mixed-doped (5% LiCl + 5% Li₂ CO₃) ZnO film had good preferred c-axis orientation when annealed both at 550 and 600 ^° C. The values of resistivity of the mixed-doped ZnO films were found to be 3 × 10⁸ and 2 × 10⁷  Ω cm with annealing temperatures at 550 and 600 ^° C, respectively.

The changes in the structure and magnetic properties of FeCoSiBNi microwires have been investigated by means of differential scanning calorimetry (DSC), x-ray diffraction (XRD), ⁵⁷Co Mössbauer spectroscopy and magnetization measurements. The crystallization temperature T_x value has been determined by DSC thermal analysis. XRD showed metastable phases (α-Fe/Co) that were formed in the nanocrystallization process. These metastable phases, embedded in the amorphous matrix, have a significant effect on magnetic ordering. Hysteresis loops and giant magneto-impedance effects measurement are used to determine the magnetic anisotropies as well as the magnetization processes.

Solid-state gas sensors based on metal-oxide thin films offer unique advantages such as compatibility with microfabrication processes and stability at high temperatures and under harsh conditions. At the same time, the sensitivity and selectivity of metal oxide sensors should be improved to compete with alternative technologies. This paper describes titanium oxide thin films for gas sensors. Titanium oxide is particularly attractive due to its high dielectric constant, which leads to extended gas-modulated space charge effects well into the film—resulting in high sensitivity, as well as for its compatibility with Si-based microprocessing technologies. The sensing properties of polycrystalline titanium oxide films (∼70 nm thick) deposited having small grain size (tens of nanometers), are described. A unique technique, using laser-induced melting and solidification of the films, that enables controlling the grain size in thin films will be discussed as a method to study grain size effects on sensing properties of titanium oxide films.

To enhance the performance of weak magnetic field sensors such as magneto-impedance (MI) effect sensors or orthogonal fluxgate sensors, the magnetic permeability of the ferromagnetic sensing elements has to be increased. In this study, the effects of annealing on the magnetic properties and sensing performance of cold-drawn Ni₈₀Fe₂₀/Cu wire sensing element have been investigated. The Ni₈₀Fe₂₀/Cu wire specimens were cold-drawn to a diameter of 34 μm and were annealed at different temperatures. The effects of final annealing temperature on the anisotropy, coercivity and MI effect of the composite wires were investigated. The results showed that the permeability increased with increasing annealing temperature until a critical value, and then decreased drastically with further increase in the annealing temperature. The decline in permeability and MI effect with further increasing annealing temperature were attributed to grain growth in the NiFe and diffusion between the NiFe and Cu. Sensitivity of the sensors with the annealed cold-drawn Ni₈₀Fe₂₀/Cu wires showed the same trend as that of permeability.

Ni₈₀Fe₂₀/Cu composite wires were developed using the pulse-reverse electrodeposition technique with the cathodic (positive) current I_c fixed at 1 mA and the anodic (negative) current I_A varied from 10 to 90% of I_c. The relationship between the magnetic properties of pulse reverse electrodeposited nanocrystalline NiFe/Cu composite wires and the anodic current was investigated. The results showed that the smaller the magnitude of the anodic current, the smaller was the average nanocrystalline grain size of the deposited material and the better was the uniformity of the surface, and consequently, the better the magnetic properties.

Systematic investigation on the effects of microwave sintering on the characteristics of nano-grained BaTiO₃ (BT) capacitor materials co-doped with yttrium (Y) and magnesium (Mg) elements was carried out. The granular structure in these materials was observed to be relatively insensitive to the sintering temperature and soaking time. The nano-sized BaTiO₃ capacitor materials possessing X7R dielectric constant–temperature (K–T) characteristics have been obtained over a wide range of sintering conditions. Transmission electron microscope (TEM) examinations revealed that the detailed microstructural study of these materials is extremely complicated. The unique K–T properties of the materials are ascribed to the duplex structure in the samples, namely finer grains of paraelectric phase and larger grains of ferroelectric phase.

Low temperature continuous-wave CO₂ laser annealing technique was successfully adopted to fabricate ferroelectric Pb(Zr_0.52Ti_0.48)O₃(PZT) thick films of different thickness on a Pt/Ti/SiO₂/Si substrate using powder-mixing and sol–gel spin coating process. X-ray diffractometer (XRD) results showed that laser annealing provides an extremely efficient way to crystallize the materials. Films of type-I with thickness of 5 μm showed cracks and rough surface morphology, indicating the importance of controlling interfacial stress and choosing appropriate size of the mixing powders. Better microstructure was observed in the type-II films. Type-II PZT film 5 μm thick and annealed at 121 W cm² exhibited better ferroelectric properties (Pr = 15.86 μ C cm²) compared to type-I PZT film. The results indicated that porosity and electrical properties of thick films can be controlled using appropriate processing parameters, suggesting the applicability of continuous-wave CO₂ laser annealing in the fabrication of PZT films.

Mechanical strain gradient induced polarization effect or flexoelectricity in perovskite-type ferroelectric and relaxor ferroelectric ceramics was investigated. The flexoelectric coefficients measured at room temperature ranged from about 1 μ C m⁻¹ for lead zirconate titanate to 100 μ C m⁻¹ for barium strontium titanate. Flexoelectric effects were discovered to be sensitive to chemical makeup, phase symmetry, and domain structures. Based on phenomenological discussion and experimental data on flexoelectricity, the present study proposed that mechanical strain gradient field could influence polarization responses in a way analogous to electric field. Flexoelectric coefficients were found to be nonlinearly enhanced by dielectric permittivity and strain gradient. Interfacial mismatch in epitaxial thin films can give rise to high strain gradients, enabling flexoelectric effects to make a significant impact in properly engineered ferroelectric heterostructure systems.

Effects of electric field-frequency, electric field-amplitude, mechanical stress, and temperature on the hysteresis area, especially the scaling form, were investigated in soft lead zirconate titanate (PZT) bulk ceramics. The hysteresis area was found to depend on the frequency and field-amplitude with the same set of exponents as the power-law scaling for both with and without stresses. The inclusion of stresses into the power-law was obtained in the form of which indicates the difference in energy dissipation between the under-stress and stress-free conditions. The power-law temperature scaling relations were obtained for hysteresis area ⟨A⟩ and remanent polarization P_r, while the coercivity E_C was found to scale linearly with temperature T. The three temperature scaling relations were also field-dependent. At fixed field amplitude E₀, the scaling relations take the forms of , P_r ∝T^−1.2322 and (E_C0 - E_C) ∝T.

Li_4(1−x)Na_4xKNb₅O₁₅ (LNKN, x = 0.25, 0.5, 0.625 and 0.75) ceramics were synthesized by conventional solid-state reaction method and studied as composite ceramics. The study considered that the LNKN ceramics are the mixed phase of perovskite (Pe) based (Na,K)NbO₃(NKN), tetragonal tungsten bronze (TTB) based K₃Li₂Nb₅O₁₅ (KLN) and LiNbO₃. The effects of mixed phase contribute to the dielectric properties at temperatures around T_max for the LNKN ceramics. Dielectric maximum occurs at a temperature around T_max=500 °C irrespective of the Li/Na composition. The largest dielectric maximum ε _maxwas observed in LNKN(x = 0.625) ceramics. Dielectric maximum ε _max seems to be proportional to the volume fraction of Pe based NKN phase. The second dielectric anomaly occurs at lower temperatures T_T–O. The variation of T_T–O seems to be caused by the change in Na/K content in the NKN phase.

This paper presents work on studying the structure and physical properties of PZT ceramics at a morphotropic phase boundary composition (Zr : Ti=52 : 48) which has been modified with different quantities of neodymium oxide, Nd₂O₃. Phase formation and microstructure development were examined by x-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques, respectively. Dielectric properties were measured, and the relationship between properties and the amount of Nd-dopant is discussed. It has been found that in the Nd-doped samples, the highest value of dielectric constant occurred for the 0.5 wt.% sample, sintered at 1200 °C, and that the maximum d₃₁ and k_p values were obtained for the 0.5 wt.% Nd composition with values of 124 pC N⁻¹ and 0.53, respectively.

The binary system of lead zirconate titanate [Pb(Zr_1/2Ti_1/2)O₃, PZT] and lead cobalt niobate [Pb(Co_1/3Nb_2/3O₃, PCoN] was fabricated using a high temperature solid state reaction method. The structure and homogeneity of the ceramics obtained have been investigated using x-ray diffraction. The morphology of the ceramics was characterized by scanning electron microscopy (SEM). The results indicated that the presence of PCoN in the solid solution decreases the structural stability of PZT perovskite phase. A transition from tetragonal to pseudo-cubic phase was observed as PCoN increased and the co-existence of tetragonal–pseudo-cubic phases occurred at composition with x = 0.3. The permittivity showed a ferroelectric to paraelectric phase transition at 236 °C with a maximum value = 39 000 at 100 Hz at the morphotropic phase boundary (MPB) composition.

In this work, barium titanate (BT) ceramic was prepared using a conventional mixed oxide method. The effect of uniaxial compressive stress on the ferroelectric properties of BT ceramics were investigated. The changes in ferroelectric properties were observed at stress up to 60 MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. The results showed that applied stress had a significant influence on the ferroelectric properties of BT ceramics. Ferroelectric characteristics, i.e. the area of the ferroelectric hysteresis (P–E) loop, the saturation polarization (P_sat), the remanent polarization (P_r) and the loop squareness (R_sq), decreased with increasing compressive stress, while the coercive field (E_c) remained constant. Stress-induced domain wall motion suppression and non-180° ferroelectric domain switching processes are responsible for the changes observed.

Microforce sensors made of PT/PZT/PT thin films were designed in the micro-Newton range. The PT/PZT/PT thin films were deposited on the Pt/Ti/SiO₂/Si substrate by the sol–gel process. Structure and the crystallinity of the deposited films were characterized. The sensing properties of the microforce sensors were measured in static state and in quasi-static state. The sensitivities of the microforce sensors with two different sizes were 0.004 and 0.040 mV μ N⁻¹ in the quasi-static state.

Degradation of lead zirconate titanate (PZT) during wafer level bonding of thermo-piezoelectric cantilevers with a CMOS-wafer was investigated. It was found that the polyimide film which serves as a height adjustment during wafer level bonding between cantilevers and the CMOS-wafer caused significant damage in the PZT sensor when polyimide was coated entirely on the PZT capacitor followed by heating to 300  °C for the bonding process. Fourier transform infrared spectroscopy (FTIR) was used to analyze the reaction product that caused PZT capacitor damage. Three different types of samples were analyzed using FTIR: a sample with coated polyimide only, a sample with a PZT capacitor with no polyimide exposed and a sample with a PZT capacitor where the polyimide has been coated, heated and then removed. NH₂ or NH₃⁺ peaks from the sample with the polyimide exposed PZT capacitor were found and these peaks were not detected on the sample with the PZT capacitor or on the polyimide coated sample only. These hydrogen ions contained in the NH₂ or NH₃ stretch during heating can lead to hydrogen atmosphere annealing which can attack PZT significantly. FTIR analysis therefore confirmed that polyimide reacted with the PZT capacitor to damage its piezoelectric properties.

Li_0.98Ni_0.7Ti_0.3O_1.92 (LNTO) cathode material for Li ion batteries was thermally synthesized using Ni/Li/TiNi film and Li/TiNi film. Structural and electrochemical properties of the synthesized electrodes were investigated by means of x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and galvanostatic charge–discharge half-cell test. A large amount of LNTO was synthesized in a Ni/Li/TiNi system compared to a Li/TiNi system, and the Ni film in the Ni/Li/TiNi system restrained Li leakage during thermal synthesis at high temperature. The surface of the annealed Ni/Li/TiNi film consisted of a peel-off layer part (Li₂O₂) and an exposed surface part (LNTO). A cell with LNTO electrode synthesized in the Ni/Li/TiNi system showed 103 mAh cm⁻² initial discharge capacity and 83% of capacity retention after 10 cycles.

A novel design of the functionally graded near-equiatomic NiTi shape memory alloys that exhibit expanded ranges of transformation temperature and stress is developed. The approach utilises the sensitivity of the alloys' thermomechanical properties with respect to heat treatment conditions. The functionally graded properties are achieved by anneal within a temperature gradient after cold work, thus to create a continuous structural variation. The optimum annealing temperature range for the Ti–50.5 at.% Ni alloy is determined to be 630–800 K. Gradient-anneal of the alloy wire in this temperature range resulted in varying thermal transformation behaviour along its length and unique Lüders-type deformation behaviour with a positive stress gradient for both the forward and the reverse transformations. Such behaviour enhances the functionality of the alloy for actuation applications.

In the present paper, ball milling is used to produce Ni_49.8Mn_28.5Ga_21.7 particles of micrometer size. Although the characteristics of transformation are not observed in the as-milled particles from 150 to 523 K from differential scanning calorimetry (DSC) study, the particles exhibit the same transformation behaviour as the bulk sample after annealing at 1073 K for 2 h. The as-annealed particles show good thermal cycling stability even after five thermal cycles. Temperature memory effect during the reverse martensitic transformation is found in the as-annealed particles. The particles exhibit regular shape, with 10M martensite structure at room temperature.

A series of biodegradable poly(L-lactide) (PLLA) and its copolymers with poly(ε-caprolactone) (PCL) is synthesized and characterized. The mechanical properties and shape memory effects are studied by means of dynamic mechanical analysis (DMA) and tensile tests. It is found that the mechanical properties are significantly affected by the polymer compositions. With the ε-caprolactone (ε-CL) content increasing, the maximum stress decreases linearly and the strain at break increases gradually. By adjusting the compositions, the polymers exhibit excellent shape memory effects and a maximum recovery stress of about 6.2 MPa can be obtained for the PCLA70 copolymer. Structure of the polymers during the shape memory process is investigated using differential scanning calorimetry (DSC) and x-ray diffraction (XRD). The polymers are observed to consist of the PLLA crystal and amorphous phase which serve as physical cross-links and reversible phase, respectively. Shape memory effect is attributed to be the deorientation of the oriented amorphous chains due to thermodynamic entropy effect.

Transformation behavior and shape memory characteristics of temperature gradient anneal (TGA) treated and thermo-mechanically treated (TMT) Ti–47Ni–3Cu(at.%) alloys were investigated by means of differential scanning calorimetry and thermal cycling tests under constant load. Both TGA treated and TMT Ti–47Ni–3Cu alloys showed B2–B19' transformation behavior. The change in M_s * by 23 K was developed in the TGA treated Ti–47Ni–3Cu alloy along the length of the sample (150 mm). TGA treated Ti–47Ni–3Cu alloy showed perfect shape memory effects. The temperature dependence of elongation (dε/dT) of a TGA treated specimen was in the range of 0.02–0.09%  K⁻¹ depending on the amount of applied stress, which was small compared to that of a TMT specimen (0.01–0.18%  K⁻¹). The temperature dependence of elongation (dε/dT) of the TGA treated specimen on cooling is almost the same as that on heating, while dε/dT of the TMT specimen on cooling is much smaller than that on heating (0.68%  K⁻¹).

Transformation behaviour, shape memory characteristics and superelasticity of Ti–(45 − x)Ni–5Cu–xV(at.%) (x= 0.5–2.0) alloys were investigated using different techniques. The B2–B19' transformation occurs when V content is less than 1.0 at.%, above which the B2–B19–B19' transformation occurs. The temperature gap between (the B2–B19 transformation start temperature) and M_s (the B19–B19' transformation start temperature) increased from 8 to 22 K with increasing V content from 1.0 to 2.0 at.%. V content dependence of (the B2–B19 transformation start temperature) was 20 K at.% ⁻¹. One-stage elongation occurred in Ti–44.5Ni–5.0Cu–0.5 V and Ti–44.0Ni–5.0Cu–1.0 V alloys, while two-stage elongation occurred in Ti–43.5Ni–5.0Cu–1.5 V and Ti–43.0Ni–5.0Cu–2.0 V alloys. Transformation hysteresis decreased from 16 to 12 K with increasing V content from 0.5 to 2.0%. The superelastic recovery ratio increased from 65.0 to 86.1% with increasing V content from 0.5 to 2.0%.

Six batches of Ti₅₀Ni_50-xCu_x alloy (x=0–25) were prepared by a melt overflow process and strips of about 550 μm thickness were fabricated by rapid solidification. Microstructures and shape memory characteristics were investigated by means of x-ray diffraction (XRD), optical microscopy, differential scanning calorimetry and thermal cycling tests under a constant load. The microstructures of the as-cast strips exhibited columnar grains normal to the strip surface. XRD showed B2–B19' martensitic transformation in the Ti₅₀Ni₅₀ binary alloy strip, while B2–B19 martensitic transformation in all the ternary alloy strips. The transformation temperature (M_s) increased with Cu-content. During cycle deformation with an applied stress of 60 MPa, the smallest transformation hysteresis and the largest elongation associated with the B2–B19 transformation were observed to be 3.5% in Ti₅₀Ni₂₅Cu₂₅ alloy strip and 3.02% in Ti₅₀Ni₄₀Cu₁₀ alloy strip.

Phase formation of NiTi alloys via solid-state diffusion reactions is investigated. Samples of different Ni–Ti compositions were synthesized from elemental powders. The study revealed that the sintered samples consisted of Ti(Ni), NiTi₂, NiTi and Ni₃Ti in co-existence. Such co-existence is not expected from the equilibrium phase diagram, but can be explained in terms of Ni/Ti inter-diffusion processes. Thermodynamic analysis indicates that formation of NiTi is not favoured in primary reactions between Ni and Ti, but can be formed via secondary reactions involving primary reaction products of NiTi₂ and Ni₃Ti. Such reactions are difficult in solid state due to the difficulties of long-distance diffusion required. The synthesized alloys were found to exhibit much reduced martensitic transformation intensity, implying low transformation volume.

Ti–40Ni–10Cu(at.%) alloy ribbons have been fabricated by melt spinning with a linear velocity of 31 m s^{− 1}. Their microstructures, transformation behavior, shape memory characteristics and superelasticity were investigated. As-spun ribbons prepared at the melt spinning temperature of 1873 K were amorphous and crystalline mixtures, below which they were crystal. The B2–B19–B19' transformation occurred in the ribbons and the maximum temperature gap between M_s' (B2–B19' transformation start temperature) and M_s (B19–B19' transformation start temperature) was 46 K. Ti–40Ni–10Cu alloy ribbons showed perfect shape memory effects even at 160 MPa and perfect superelasticity over a temperature range of 13 K. The transformation hysteresis of Ti–40Ni–10Cu alloy ribbons associated with the B2–B19 transformation was 8 K. Rapid solidification was found to be effective in increasing the critical stress for slip of a Ti–40Ni–10Cu alloy without overlapping the B2–B19 and B19–B19' transformations.

Point defects in a crystalline solid can generate a time-dependent strain under the application of an external stress due to the reorientation of the point defects. This so-called Snoek effect is first applied to develop high damping alloys in bcc based alloys. It is experimentally confirmed that β-Ti alloys show high damping capacity in the temperature range of 473–573 K when a certain amount of oxygen is alloyed in solid solution state. The damping behavior is attributed to the strain relaxation process of oxygen in the bcc structured alloy. Both the damping capacity and the temperature range where the damping peaks occur depend on the composition of the base Ti alloy, as well as the oxygen content. Since the damping behavior of this new type of damping alloy is dictated by the relaxation processes of interstitial solute in the bcc lattice, composition design is essential in order to control the temperature dependent damping behavior.

The thermal expansion behaviors of the unit-cell volume of the Dy₂AlFe₈Mn₈ compound from 104 to 643 K and its spontaneous magnetostrictions are investigated by means of x-ray dilatometry and magnetization measurements. The results show that there exists a negative thermal expansion in the temperature range 150–230 K. The average coefficient of the thermal expansion is . The spontaneous magnetostrictive deformations from 104 to 235 K have been calculated. The results show that the spontaneous volume magnetostrictive deformation ω _s increases from 4.4 × 10^{− 3} at 104 K to 7.1 × 10^{− 3} at 150 K with the temperature increasing, and then decreases with the temperature increasing further. The spontaneous linear magnetostrictive deformation λ _c along the c-axis decreases with the temperature increasing while deformation in the basal-plane λ _a increases from 0.9 × 10^{− 3} at 104 K to 2.4 × 10^{− 3} at 145 K with the temperature increasing and then decreases with the temperature increasing further.

Anatase, brookite and rutile type nitrogen doped titania nanocrystals (TiO_2−xN_y) which possessed beige color were successfully prepared as single phase using homogeneous precipitation-solvothermal process in TiCl₃-hexamethylenetetramine (C₆H₁₂N₄) aqueous and alcohol solutions at temperature as low as 190 °C. The phase composition, crystallinity, microstructure, specific surface area, nitrogen doped amount and photocatalytic activity of titania powders were greatly changed depending on pH, temperature and kind of treatment alcohols. TiO_2−xN_y films with various phases and high surface area could be prepared using a novel low temperature process, i.e. a spin-coating of TiO_2−xN_y powder using an organic binder followed by oxygen plasma treatment below 60 °C within a short time period. The nitrogen doped yellowish titania powders and films possessed excellent light absorption up to 565 nm, and showed excellent visible light induced photocatalytic ability under irradiation of visible light of wavelength >510 nm. The relationship between the phase composition, photocatalytic activity and hydrophilic ability of the film was investigated in detail. The effects of film thickness, surface roughness and porosity on the photocatalytic activity were discussed.

Two methods for preparing piezoelectric fluorocarbon polymers with cellular structure (ferroelectrets) are introduced. Piezoelectric activity of laminated fluorocarbon films made from polytetrafluoroethylene (PTFE) and fluoroethylenepropylene (FEP) is characterized by quasistatic measurement of piezoelectric d₃₃ coefficient, while the thermal stability of d₃₃ is investigated by their isothermal decay. The results show that the quasistatic d₃₃-coefficients between 500 and 2200 pC/N are obtained for such fluorocarbon films; d₃₃-coefficients are relatively independent of the static pressure in the range of 20 kPa; comparing to cellular polypropylene (PP) film the new fluorocarbon films show not only higher values of d₃₃, but also much better thermal stability; moreover, thermal stability of the fluorocarbon film can be further improved by the process of pre-ageing.

Three new photochromic diarylethenes bearing cyano groups at the ortho-, meta-, or para-positions of both terminal phenyl rings, namely 1,2-bis(2-methyl-5-(2-cyanophenyl)-3-thienyl)perfluorocyclopentene (1a), 1,2-bis(2-methyl-5-(3-cyanophenyl)-3-thienyl)perfluorocyclopentene (2a), and 1,2-bis(2-methyl-5-(4-cyanophenyl)-3-thienyl)perfluorocyclopentene (3a), have been synthesized. The substituent position effects on their optoelectronic properties, including photochromism, fluorescence and electrochemical properties in solution, were investigated systematically. The molar absorption coefficient (ε = 7.48 × 10⁴  L mol^{− 1}  cm^{− 1}), the absorption maxima and the quantum cyclization yield (Φ _{0 − c} = 0.53) of 3a are the biggest while its cycloreversion quantum yield (Φ _{c − 0} = 0.004) is the smallest. In hexane, the fluorescent emission peaks of diarylethenes 1a, 2a and 3a showed a bathochromic shift upon increasing concentration. The oxidations of diarylethenes 1a, 2a and 3a are initiated at 1.85, 1.58 and 1.58 V, respectively, which are higher than those of their closed-ring forms 1b, 2b and 3b (1.61, 1.43 and 1.49 V, respectively). The results indicate that the optoelectronic features of diarylethenes 1, 2 and 3 are distinctly different, which may be attributed to the different electron-withdrawing ability and steric effect of cyano groups with different substituted positions.

Europium-doped Y_1−xGd_xAlO₃ perovskite (YAP) nanophosphors were synthesized by a solvothermal method. A YAP phase without impurity was formed from phosphors sintered at 1100 ° C. All the phosphors except YAlO₃ can be estimated as mixed cubic and orthorhombic YAP phase. With the increase in Gd, the crystallinity was changed from simple cubic to q mixed phase of cubic and orthorhombic. Due to a ⁵D₀→⁷F₂ forced electric dipole transition of Eu³⁺, the nanophosphors with two mixed phases emitted radiation of red light with a 614 nm wavelength, whose brightness was dramatically increased by a factor 8 in comparison to that of the cubic perovskite phase. It is ascribed to the enhancement of non-symmetric environment for the Eu³⁺ in the nanophosphors with two mixed phases. The intensity ratios (I_ED/MD) between the structural hypersensitive force electric dipole transition, ⁵D₀→⁷F₂, and the intensity of the magnetic dipole transition, ⁵D₀→⁷F₁, are 0.4 for cubic phase and 1.4 for mixed phase.

Nanodevices based on semiconductor nanoarrays have demonstrated many novel electronic, optical and chemical properties. In this work, two simple and controllable solution-based methods for growing well-aligned ZnO nanoarrays on zinc substrate are reported. Photoluminescence (PL) spectrum results revealed that the ZnO nanoarrays may have potential applications as building blocks for 'bottom-up' designed photonic and electronic device applications. Furthermore, well-aligned ZnS nanotube arrays have been successfully synthesized by employing the ZnO nanorod arrays as the sacrificial template through the thioglycolic acid-assisted solution reaction route.

The characteristics of an InP/InGaAs pnp heterostructure-emitter bipolar transistor is investigated using theoretical analysis and experimental methods. Although the valence band discontinuity at the InP/InGaAs heterojunction is relatively large, the addition of a heavily-doped, as well as thin p⁺-InGaAs emitter layer between p-InP confinement and n⁺-InGaAs base layers effectively eliminates the potential spike at the emitter–base junction, lowers the emitter–collector offset voltage, and increases the potential barrier for electrons simultaneously. Experimentally, a high current gain of 88 and a low offset voltage of 54 mV could be achieved.

A phenanthrenyl-substituted diarylethene derivative (1,2-bis[5-phenanthryl-2-methylthiophen-3-yl] perfluorocyclopentene, Ph-BMTFP) has been synthesized and its optoelectronic properties have been investigated. The photochromic reactivity of Ph-BMTFP was examined in hexane solution as well as in poly(methyl methacrylate) (PMMA) amorphous film. Upon irradiation with 313 nm UV light, the colorless solution turned purple, in which a visible absorption band was observed at 555 nm. In PMMA film, the new broad absorption band at λ _max = 580 nm appeared when it was irradiated by 313 nm UV light. The compound exhibited good fluorescence in hexane solution and its fluorescence intensity decreased along with the photochromic reactivity upon irradiation with 313 nm UV light. This property could be potentially applied to high-density optical memory with fluorescence readout method. The holographic optical storage was performed successfully using Ph-BMTFP as the recording medium and polarization multiplexing holograms recording can effectively increase the information storage capacity of the holographic data storage.

Effects of strontium doping on ionic conductivity of Sm₂O₃-doped ceria (samarium-doped ceria (SDC)) were investigated. The distribution and average radius of oxygen vacancies by co-doping divalent and trivalent cations were calculated from a hard-sphere model. Experimental results exhibit that the best conductivity for Ce_0.78Sm_0.2Sr_0.02O_1.88 (0.061 S cm⁻¹) specimen is twice that of Ce_0.8Sm_0.2O_1.9 (0.0371 S cm⁻¹) at 800 ^°C. A decrease of 50 ^°C in the working temperature of SDC was developed by modifying the dopant concentration, average binding energy and ionic radius of the dopant. The results confirm the Sm³⁺ and Sr²⁺ co-doped ceria material as a potential electrolyte for intermediate-temperature solid oxide fuel cell applications.

Different configurations of Fe-doped TiO₂ thin films deposited on both quartz glass and heavily doped p-type silicon substrates were prepared by the sol–gel method. Oxygen-sensing properties of the TiO₂ thin films were measured through the variations in resistivity under a low operating temperature of 300 °C using a micro-current instrument. Extraordinary oxygen sensitivity up to about 200 times of resistance ratio appeared only in the configuration of TiO₂ thin film deposited on the heavy doped p-type silicon substrate with Fe doping of 4–6 mol %, in which the rutile phase content was maximum. The high oxygen sensitivity was induced by the extrinsic positive charge gained and was controlled by both the rutile phase content in the thin film and the positive charge transmitted from the heavily doped p-type single crystal silicon to the thin film.

Transparent conducting Sb-doped SnO₂ (antimony-doped tin oxide: ATO) films were prepared on Corning glass substrate by dc magnetron sputtering using SnO₂ mixed with 6 wt.% of Sb at various substrate temperatures of 100–600 °C and dc powers of 100–200 W. All ATO films were deposited with a thickness of 300 nm. X-ray defractometer (XRD) measurements showed the ATO films to be crystallized with strong (101) orientation as substrate temperature increases over 300 °C. Grain size was calculated from the XRD spectra using the Scherrer equation. The ATO film in this work had a resistivity of order 10^{− 3} and carrier concentration of order 10²⁰.

To accurately measure temperatures, a novel temperature sensor based on a quartz tuning fork resonator has been designed. The principle of the quartz tuning fork temperature sensor is that the resonant frequency of the quartz resonator changes with the variation in temperature. This type of tuning fork resonator has been designed with a new doubly rotated cut work at flexural vibration mode as temperature sensor. The characteristics of the temperature sensor were evaluated and the results sufficiently met the target of development for temperature sensor. The theoretical model for temperature sensing has been developed and built. The sensor structure was analysed by finite element method (FEM) and optimized, including tuning fork geometry, tine electrode pattern and the sensor's elements size. The performance curve of output versus measured temperature is given. The results from theoretical analysis and experiments indicate that the sensor's sensitivity can reach 60 ppm °C⁻¹ with the measured temperature range varying from 0 to 100 °C.

Synthesis of amorphous Nd–Fe–B nanoparticles under an aqueous borohydride solution and the magnetic behavior of the amorphous structure after mild heat treatment with CaH₂ have been studied. The ultra-fine Nd–Fe–B nanoparticles were first synthesized from reduction of FeCl₂ and NdCl₃ using NaBH₄ as a reducing agent in aqueous solution. The as-prepared precipitates, which were composed of Fe–B phase and Nd oxide phase, were then mixed with calcium hydride. The Nd oxide in the precipitates was reduced by CaH₂ and then Nd diffused into the Fe–B phase via reduction–diffusion process. After the as-obtained Nd–Fe–B material was washed with acetic acid, its magnetic property was measured showing its ferromagnetic behavior.

Ag deposited TiO₂  (Ag/TiO₂) particles were synthesized by laser ablation of silver and titanium targets in de-ionized (DI) water. Post-annealing makes the structure stable and the materials change to crystalline state. It is a new approach to form Ag/TiO₂ particles with a simple system and non-toxic materials. TiO₂ particles with size from 20 to 30 nm coated with silver nano-clusters were observed. The silver nano-clusters can enhance the absorption capability of TiO₂ photocatalysts. UV-vis spectrum analysis shows that there is a strong absorption peak at around 400 nm. It is attributed to Ag nanoparticles surface plasmon resonance (SPR) effect. This effect helps to improve the spectral characteristics of TiO₂ nanoparticles with its absorption spectra shifted to a longer wavelength region. From the above properties, Ag/TiO₂ nanoparticles would have new potential applications in photocatalyst and photo-anode.

A three-dimensional (3D) constitutive model based on a statically constrained microplane theory with volumetric–deviatoric split is proposed for polycrystalline shape memory alloys (SMAs) under multiaxial loading paths. Microplane governing equations are 1D stress–strain relations for normal and shear stresses on each microplane, in which suitable relationships between the microscopic and macroscopic quantities are considered so that switching between elastic and inelastic local responses automatically occurs according to the macroscopic response of SMA without additional constraint. Shear stress on each microplane is expressed by the resultant shear component within the plane to overcome directional bias and to prevent the appearance of shear strain in a pure axial loading or axial strain in a pure shear loading while microplane formulations based on two shear directions may predict such impractical results. The behaviour of SMA under simple and complicated loadings has been studied. In nonproportional loading paths, the model shows interaction between stress components, as well as deviation from normality. Predicted results from the model are in good agreement with those of the existing theoretical and experimental investigations.

Electrically conducting polyaniline (PANI)–magnetic oxide (Fe₃ O₄) composites were synthesized by emulsion polymerization in the presence of dodecyl benzene sulfonic acid (DBSA) as the surfactant and dopant and ammonium persulfate (APS) as the oxidant. Transmission electron microscopy (TEM) indicates that the composite has a magnetic core and an electric shell and the modification has prevented the aggregation of Fe₃ O₄ nanoparticles effectively. The electromagnetic parameter measurements (ε'', ε', μ'' and μ') in the range of 2–18 GHz prove that Fe₃ O₄ in the Fe₃ O₄/PANI/DBSA is responsible for the electric and ferromagnetic behavior of the composites. As a result, the electromagnetic parameters can be designed by adjusting the content of the Fe₃ O₄. The microwave absorption of functionally graded material (FGM) was simulated by the computer according to the principle of impedance match and the calculated results agreed quite well with the experimentally measured data (R<−20 dB, Δf>4 GHz).

First-principle density-functional calculations were performed to investigate the electronic structures, atomic structures and formation energies for native defects, oxygen impurities and related complexes in Zn₃N₂. The formation energy calculated shows that the configurations of substitutional O for N and O plus a N vacancy complex (O_N(1)–V_N(2)) are energetically favorable in both N-rich and Zn-rich growth conditions. The electronic structures demonstrate that N vacancy, substitutional O, and O_N(1)–V_N(2) complex defective Zn₃ N₂ are of n-type conduction character.

On the basis of Pt/InAlAs metal–semiconductor (MS) structure, an interesting hydrogen sensor is fabricated. The Pt/InAlAs Schottky diode-type hydrogen sensor studied exhibits significant sensing performance including high relative sensitivity ratio (S_r) of about 2600%, widespread reverse voltage regime (0∼ - 5 V), and stable hydrogen sensing current density–voltage (J–V) curves. The calculated Schottky barrier height change and series resistance variation from the thermionic emission model and Norde method are 87.0 meV and 288 Ω, respectively. The negative temperature dependence on S_r is due to the lower hydrogen coverage at higher temperature. Yet, the positive temperature dependence on Δ I is caused by thermal effect. Based on the excellent integration compatibility with InP-based electronic devices, the device studied does provide potential for high-performance sensor array applications.

Photonic crystals (PCs) containing defects have important applications in optical filtering with super narrow transmission band and photo phase adjustment. Resonance transmission bands in one-dimensional PCs with a defect mode are calculated by the transfer matrix method. The effect of two primitive dielectric refractive index ratios and position of the defect in PCs on filter quality are analyzed. The photonic band gap of PCs, the narrow resonance transmission band made by defect, and the relationship between refractive index of defect layer and the peak value of narrow resonance transmission band are discussed. The physical mechanisms can be explained by the photonic potential well and potential barrier scattering for photons.

A new method to measure the piezoelectric constants of d₃₃^f and d₃₁^f of thin films using x-ray diffraction (XRD) is proposed. Piezoelectric constant d₃₃^f is calculated from the measurement of change in out-of-plane lattice spacing of the piezoelectric films while piezoelectric constant d₃₁^f is obtained from the change in the slope of d_{ϕ ψ} versus sin² ψ curves before and after applying an electric field over the film. This method improves the accuracy by directly measuring the strains in the films induced by the externally applied electric field instead of the surface displacement that could easily be interfered with by environment/vibration and surface morphology of the thin films.

We present first-principles spin polarized calculations of the electronic structure and magnetic properties of Cu-doped in ZnO. We show that it is likely for Cu to order ferromagnetically in ZnO, forming a dilute magnetic semiconductor. The coupling between Cu atoms is found to be ferromagnetic despite Cu being nonmagnetic in its natural phase. The Cu-doped ZnO is shown to possess a magnetic moment of 1μ _B per Cu, with a spin-polarized impurity band at the top of the ZnO valence band. The impurity band is found to primarily arise from the hybridization of the Cu 3d level with O 2p states. Analyzing the calculated density of states, it is proposed that the origin of the stabilization of the ferromagnetism is a double-exchange mechanism. It was also found that the magnetic couplings are sensitive to the distance between Cu atoms and ferromagnetic coupling is favorable for the far configuration. These results are consistent with the recent experimental discovery of ferromagnetism in Cu-doped ZnO.