Table of contents

Drift behaviours of quasifree electrons in nonpolar condensed matters (dense gases, liquids and solids) under uniform electric fields are reported in this review. Measurements have shown that, in some sorts of nonpolar fluid, zero-field electron mobility depends strongly on the number density of atom or molecule comprising the matters from dilute gas to solid phase. The dependence was explained by the fact that in the condensed phase new energy levels of the valence electrons are formed through a regular spatial arrangement of long-range order, the crystal lattice, due to the Pauli exclusion principle, and that excess electrons move in the conduction band. The electron drift motion under the fields in the conduction band is also described.

Structural, magnetic and magnetocaloric properties of Dy(Co_1−xNi_x)₂ (x = 0, 0.02, 0.04, 0.06 and 0.1) alloys were studied by x-ray diffraction (XRD) and magnetic measurements. The XRD analysis shows that all samples crystallize in the cubic MgCu₂-type structure. The ordering temperature T_C decreases from 143 to 92 K with increasing Ni content up to 0.1, which is attributed to the decrease in the exchange interactions. The isothermal entropy changes ΔS as a function of temperature in different magnetic fields were determined. All samples show a large isothermal entropy change and ΔS_max remains approximately constant over the temperature range limited by the Curie temperatures of the Dy(Co_1−xNi_x)₂ series (92–143 K). The relative cooling power increases with the Ni content; it passes from 287 to 344 J kg⁻¹ for x varying from 0 to 0.1 under 5 T. The origin of the magnetocaloric effect in Dy(Co_1−xNi_x)₂ alloys is discussed.

Here we report a systematic study of magnetic, electronic and microstructural properties of Cu-doped and Cu and Al codoped ZnO thin films, grown epitaxially on a (0 0 0 1) sapphire substrate by the pulsed laser deposition technique. The films were annealed in oxygen at high temperature (600 °C) and their properties were compared with the as deposited films in order to study the role of defects like oxygen vacancies on the ferromagnetic properties. The doping of ZnO : Cu specimens with Al increased the carrier concentration by three orders of magnitude (from 10¹⁷ to 10²⁰ cm⁻³) without altering the ferromagnetic ordering. On the other hand, a reduction in oxygen vacancies concentration brought about by high temperature annealing in oxygen had a large detrimental effect on ferromagnetism. These results tend to eliminate a free carrier mediated mechanism and point towards a defect mediated mechanism, such as a bound-magnetic-polaron mediated exchange, as being responsible for stabilizing long-range ferromagnetic ordering in these systems.

The static and dynamic features of magnetization are investigated using dc magnetization and ac susceptibility measurements on La_1−δMn_0.7Fe_0.3O₃ for δ = 0 and 0.13. The results indicate that short range ferromagnetic clusters coexist with the glassy magnetic state. The analysis on the frequency dependence of spin freezing temperature (T_f) using the Vogel–Fulcher law and the dynamical scaling behaviour near T_f indicates that the spin freezing temperature behaves like a spin-glass transition temperature for both the compounds. The cluster-glass states of both the compounds exhibit similar characteristic features.

The effect of Zr on the microstructure, microchemistry and coercivity of Sm(Co_balCu_0.08Fe_{0. 10}Zr_x)_8.5 (x = 0–0.10) magnets has been systematically investigated. The presence of Zr is responsible for the formation of the lamella structure. With increasing Zr content, a cellular-like structure gradually develops while the density of the lamella phase increases. A proper Zr content (0.015–0.060 at.%) is the key to form a complete and uniform cellular structure. Microchemistry data show that the Cu content in the cell boundaries in the magnet with 0.04 at.% Zr is higher than that with 0.015 at.% Zr, although both samples have similar microstructure morphologies. Higher coercivity is obtained in samples where the domain walls (DWs) are pinned at cell boundaries. For Zr-free or higher Zr samples, DWs nucleated at grain boundaries are responsible for the reduction in coercivity. During isothermal ageing, at a fixed Zr content, the coercivity is developed with increasing ageing time. These results clearly show that Zr plays an important role in the formation of a uniform cellular structure with the right microchemistry and that a critical amount of Zr is needed for the optimum magnetic properties.

The strain effect on the magnetotransport properties in La_0.9Sr_0.1MnO₃ films epitaxially deposited on SrTiO₃ (STO) and LaAlO₃ (LAO) substrates, is demonstrated. Large compressive strain is formed in the films on the LAO substrate; however, that on the STO is subject to a small tensile strain. Strain relaxation of films grown on both substrates results in the formation of a spin-canted antiferromagnetic (AFM) insulative phase, causing the increase in resistivity with decreasing temperature. The characteristics of the AFM insulative phase become apparent with increasing film thickness, which leads to a clear AFM transition in the films grown on LAO and a reduction of magnetization and Curie temperature in those on STO. The magnetoresistance effect of the films is also consistent with the above results.

This paper describes the effects of magnetic field on rolling contact performance of steel discs and presents an investigation into the mechanisms governing these effects by applying contact mechanics and magnetism theory.

The tests were carried out in disc-on-disc contact configuration using two contact conditions, i.e. pure rolling and rolling with 10% sliding. Also two horizontal static magnetic fields of 0.4 and 1.1 T created by permanent magnets were applied. The results of scanning electron microscopy observations reveal that finer wear particles and smoother worn surfaces are produced in the presence of a magnetic field. The smoother surfaces are also confirmed by surface roughness measurements. For generation of the finer wear particles, it is considered that the subsurface crack initiation point is moved towards the surface due to the magnetic field.

Wear amounts are decreased in the magnetic fields under pure rolling conditions. However, at rolling with 10% sliding, the wear amounts are increased in the magnetic fields, even though finer particles and smoother surfaces are observed. Both tendencies are explained by calculating the number of cycles required to generate wear particles, which were reduced due to the magnetic field presence.

It is considered, therefore, that domain walls near the contact region are caught by dislocations when the specimen is magnetized and part of the energy for magnetization activates the dislocation movement resulting in crack initiation.

A numerical analysis of three-dimensional keyhole dynamics is accomplished for the laser drilling of 2 mm thickness carbon steel. The molten and re-solidified free surface is tracked by the volume of fluid method. One of the important features, referred to as the multiple reflections of a laser beam in a keyhole, is implemented in real-time during the computation. Fresnel reflection theory is adopted to describe the energy absorption mechanism. In particular, the effect of polarization of the laser is investigated through the Fresnel reflection model. Analyses are carried out for both circularly and linearly polarized beams. The simulation results show that the keyhole under a circularly polarized laser is symmetric along the beam axis, while for the case of a linearly polarized beam the keyhole is asymmetric and is stretched along the direction of polarization.

The photoluminescence properties of doped SnO₂ have been investigated. In Eu³⁺, Sb³⁺ and Ca²⁺ doped SnO₂, fine structure emissions in the range from 580 to 725 nm are clearly observed. These fine structure emissions have been ascribed to electronic transitions from the split D, C, B and A bands to the ground state under the famous Jahn–Teller effect and the spin–orbit interaction of the dopant induced Sn²⁺ ions in the doped SnO₂. The formation of Sn²⁺ ions in the doped systems is ascribed to compensate for the discrepancy of the structure and the electronic charge between the host cation and the impurity.

The problem of simultaneously enhancing sensitivity and noise immunity of microcantilevers is investigated. The dependence of deflection and resonant frequency of a microcantilever on its dimensions is studied. A principle to increase deflection and resonant frequency simultaneously is established. Several cantilevers agreeing with this principle are investigated using analytical models and are compared with FEM simulations. Using these results, a cantilever profile that achieves a larger deflection and a larger resonant frequency compared with uniform cantilevers is proposed to be used in sensor elements.

Pseudomorphic GaAs_1−ySb_y quantum wells with 0.16 ≤ y ≤ 0.69 on (0 0 1) InP substrates have been grown using metal–organic chemical vapour deposition. High resolution x-ray diffraction and transmission electron microscopy analysis are used to quantify the layer thicknesses and compositions. Studies of the optical properties suggest that a transition from type-I to type-II band alignment occurs at an antimony concentration of approximately y = 0.30. The interband optical transition energies simulated using a ten-band k·p Hamiltonian are compared with the experimental values deduced from photoluminescence spectroscopy. The valence band offset bowing parameter is evaluated in the context of the experimental transition energies. For low Sb-contents, reasonable agreement (<7% deviation) is achieved between theory and experiment for the primary optical transitions. However, at higher Sb-content, there is significant deviation between the measured transition energies and the k·p based theory, possibly a result of a non-ideal interface and/or heterogeneous ternary well.

Heterostructured ZnO : S/ZnO (S-doped ZnO ribbon with ZnO nanoteeth) nanosaws were synthesized by a one-step catalyst-free process through the chemical vapour transport and condensation method. Optimum selectivity and maximum nanosaw densities are obtained for growth temperatures in the range 400–450 °C. Our study suggests that the ribbons were ZnO : S while the teeth were only ZnO. Nanorods, nanoairplane, nanobelts and smooth surface nanotip-like structures were also obtained in our experiment at different growth temperatures. The photoluminescence spectrum of the nanosaws showed a strong visible emission band compared with undoped ZnO powder at room temperature. This strong visible emission in the hetrostructured nanosaws might be useful as a future UV-excited phosphor for producing bright and broad visible-wavelength light.

A new universal principle of selective registration of electromagnetic radiation by means of silicon-based solid-state two-barrier structures is studied. In such structures, due to the interaction of oppositely directed photocurrents caused by potential barriers, it becomes possible to selectively register narrow spectral regions selected from the integral radiation flow, as well as to define the unknown length of a monochromatic wave. The influence of the base width and of outside-the-base areas of the two-barrier structure on photocurrent behaviour and on spectrophotometric properties of the photo-detector is studied.

Mo/γ-In₂Se₃/ZnO : Al diode structures have been grown by vacuum deposition. In order to study the influence of the ZnO : Al electrode on the diode properties, ZnO : Al conductive and insulating films have been deposited by rf magnetron sputtering using a single Al₂O₃ doped ZnO target. These films have been characterized before their use in diodes. The electrical properties of ZnO : Al are controlled by the oxygen partial pressure during deposition. The effect of the composition on the I–V characteristics of γ-In₂Se₃ based diodes has been investigated. When γ-In₂Se₃ is doped with manganese there is no photovoltaic effect while there is when it is pure. It is shown that the I–V curves agree with Schottky theory only in the case of pure γ-In₂Se₃. When it is doped the I–V curves agree well with the trap-controlled space charge limited transport theory, which is attributed to the presence of a band of localized states present in the band gap of γ-In₂Se₃ after Mn doping.

Optical properties of CaF₂, grown by a controlled Bridgman–Stockbarger technique, are studied by CuBr and SrBr₂ vapour lasers. Absorption losses are determined as a function of the grown crystal volume, the crystallization front (CF), and the real crystallization rate. It is found that the absorption losses are relatively independent of the transmitted wavelengths in a wide spectral range from the deep ultraviolet (DUV) to the middle infrared (MIR) spectral region and their minimum corresponds to CF positions within the upper half of the adiabatic furnace zone, where the CR reaches a constant value slightly higher than the speed of crucible movement. The crystal quality conforms to laser grade CaF₂ for the DUV, visible and MIR spectral regions and may be controlled efficiently by introducing an appropriate systematic correction in the furnace temperature field, which shifts the CF position.

Pentacene based junctions with Al on both p-Si(1 0 0) and indium tin oxide (ITO) substrates have been analysed using impedance spectroscopy (100 Hz–20 MHz) and dc-current versus voltage measurements. Conduction mechanisms match well with the space charge limited current model with exponential trap charge distributions. Impedance studies reveal the Schottky behaviour for both the devices. The differences between p-Si/pentacene/Al and ITO/pentacene/Al devices have been explained by modelling equivalent circuits, with one and two RC elements, respectively. The switch-over field from ohmic conduction to space charge limited conduction, charge concentration as a function of voltage and bias dependent series resistance have been estimated for both the cases.

In this study, the feasibility of using wafer-bonding technology to fabricate a GaSb semiconductor on GaAs substrates for potentially creating a GaSb-on-insulator structure has been demonstrated. A GaSb wafer has been bonded on two types of GaAs substrates: (1) a regular single crystal semi-insulating GaAs substrate and (2) the GaAs wafers with pre-deposited low-temperature amorphous α-(Ga,As) layers. The microstructures and interface adhesion studies have been carried out on these wafer-bonded semiconductors. It has been found that the GaSb-on-α-(Ga,As) wafers have shown enhanced interface adhesion and lower temperature bonding capability.

This paper presents an experimental investigation of the plasma ignition in a dielectric barrier surface discharge in air at atmospheric pressure. CCD pictures of the discharge are compared with electrical measurements. A detailed study of the current peaks during the positive half period of the applied voltage has been performed. CCD pictures of single discharges events have been taken. They show synchronous breakdowns of plasma filaments, corresponding to current intensities of several amperes. It is shown that each plasma filament transfers a current of about 40 mA. The influence of adsorbed electrons on the synchronization of the plasma filaments is discussed. The length of the filaments increases during the half period and can be plotted as a linear function of the difference between applied and ignition voltages. The differences between the discharges of positive and negative half periods are presented. The discharges of the negative half period consist of diffuse spots of shorter lengths and are characterized by low currents (several milliamperes), and individual breakdowns.

Three-dimensional simulation of arc motion is presented for conditions representative of those for a railplug ignitor. A railplug ignitor is a miniature rail-gun used to deliver an arc ignition source for internal combustion engine applications. Computations explored the influence of the railplug geometry, effects of an external magnetic field, and impact of the circuit current on arc velocity. One underlying question about arc motion in railplug systems has been the influence of the expansion velocity associated with energy deposition on arc motion. A single open end muzzle would result in higher velocities if the expansion effects are dominant. This was tested by simulating two types of geometries, single open end and double open end muzzles. The double open end configuration was shown to have faster arc propagation velocities. A discussion of the mechanisms is presented. A simple scaling analysis was found to explain the increased arc propagation velocity associated with application of an external magnetic field. Increasing the circuit current was found to increase the final arc propagation velocity, although the early time velocities were slower for larger currents.

Vanadium pentoxide (V₂O₅) thin films were deposited onto Si (1 0 0) substrates using dc and pulsed dc reactive magnetron sputtering at 26, 100 and 300 °C to investigate the influence of substrate temperature and sputtering mode on their structural and mechanical properties. X-ray diffraction, Raman spectroscopy and scanning electron microscopy revealed that the structural characteristics and the surface morphology of the V₂O₅ films depend on both sputtering mode and deposition temperature. With increasing deposition temperature, the films deposited by dc sputtering show a transition from amorphous at room temperature to polycrystalline growth with a preferred (2 0 0) orientation. This leads to an increase in hardness and elastic modulus of the films from 3.2 ± 0.1 GPa and 79.4 ± 3.2 GPa at 26 °C to 4.8 ± 0.6 GPa and 129.2 ± 6.4 GPa at 300 °C, respectively. In contrast, the films deposited by pulsed dc sputtering exhibit a polycrystalline α-V₂O₅ structure over the whole temperature range. The hardness of these films decreases with increasing deposition temperature while Young's modulus is almost unaffected.

Long-lasting problems concerning peculiar statistical behaviour of high populated electron avalanches have been analysed. These avalanches are precursors of streamer breakdown in gases. The present streamer theory fails in explaining severe systematic deviations from the Furry statistics that is believed to be a governing statistical law. Such a deviated behaviour of high populated avalanches seems to be a consequence of a special pre-breakdown mechanism that is rather different from that known so far in discharge physics. This analysis tends towards formulating a modified theoretical concept supplementing the streamer theory by a new statistical view of pre-streamer states. The correctness of the concept is corroborated by a series of experiments.

A mathematical model for the primary chemical processes occurring in 1 J/pulse electrical discharges in water has been developed. The discharge channel is divided into two zones: the core and the recombination region. The core is a very narrow (ca 10 µm) part of the channel where high temperature initiation reactions take place and where the majority of molecular hydrogen and 47% of the molecular oxygen are formed. The recombination region is a 200 µm radius zone where additional reactions such as hydrogen peroxide formation take place. The temperature in the core ranged from 5000 K at the centre to 2000 K at the boundary and the pressure, the only adjustable parameter in the system, was found to be 14 atm. The model describes for the first time how molecular oxygen is formed in an underwater discharge and it is also able to describe the experimentally observed stoichiometry of H₂, O₂ and H₂O₂ formation. The concentration and temperature profiles inside the discharge channel as well as a general scheme for the water dissociation and molecular species formation are also reported.

The surface of ethylene-propylene-diene monomer (EPDM) rubber was treated in N₂/Ar and N₂/H₂/Ar RF plasmas in order to achieve similar or better adhesion properties than NBR (acrylonitrile-butadiene) rubber, nowadays used as thermal protection of rocket chambers. The surface properties were studied by contact angle measurements and by x-ray photoelectron spectroscopy (XPS). The treated surfaces of the EPDM samples show a significant reduction in the contact angle measurement, indicating an increase in the surface energy. XPS analyses show the incorporation of polar nitrogen- and oxygen-containing groups on the rubber surface. After plasma treatment the presence of oxygen is observed due to surface oxidation which occurs when the samples are exposed to the air. Atomic force microscopy and scanning electron microscopy analyses indicate a decrease in the EPDM rubber surface roughness, promoted by surface etching during the plasma treatment. Strength tests indicate improvement of about 30% and 110% in the adhesion strength for the plasma treated EPDM/polyurethane liner interface and for the EPDM/epoxy adhesive interface, respectively. The adhesion strength of the EPDM/liner is similar to that obtained for the NBR/liner, which indicates that EPDM rubber can safely be used as thermal protection of the solid propellant rocket chamber.

Vacuum arc erosion measurements were performed on copper cathodes having different surface roughness and surface patterns in 10⁻⁵ Torr vacuum (1.3324 mPa), in an external magnetic field of 0.04 T. Different surface patterns and surface roughness were created by grit blasting with alumina grits (G-cathodes) and grinding with silicon carbide emery paper (E-cathodes). The erosion rates of these cathodes were obtained by measuring the weight loss of the electrode after igniting as many as 135 arc pulses, each of which was 500 µs long at an arc current of 125 A. The erosion rates measured indicate that erosion rates decrease with decreasing roughness levels. Results obtained indicate that both surface roughness and surface patterns affect the erosion rate. Having patterns perpendicular to the direction of cathode spot movement gives lower erosion rates than having patterns parallel to arc movement. Isotropic surfaces give lower erosion rates than patterned surfaces at the same roughness.

The influence of a highly pronounced non-equilibrium characteristic of the electron energy distribution function in a stratified dc glow discharge on the process of dust particle charging in a complex plasma is taken into account for the first time. The calculated particle charge spatial distribution is essentially non-homogeneous and it can explain the vortex motion of particles at the periphery of a dusty cloud obtained in experiments.

We have presented a numerical simulation of the deposition of dielectric material using an insulating porous template. A Maxwellian distribution has been used to calculate the original ion velocity when the ion leaves the plasma and enters the sheath. The microscopic electrical field over the template is considered to affect the ion motion. It is found that the electron temperature and nanopore structure can change the ion deposition rate effectively. However, the deposition rate decreases only slightly with the rise in plasma density and does not rely on the substrate bias obviously for the reason that the effect of electrical field near the template is limited. The result of our paper indicates that the templated i-PVD of dielectric nanodots is quite different from the templated i-PVD of metallic nanodots, and new ways should be tried for the plasma to fabricate dielectric nanodots using a porous template to make the effect from the electrical field and the substrate bias stronger.

The main physical processes occurring in plasma electron source with large cross-section beam are shown. The main factors influencing the emission properties of the plasma emitter are revealed. A physical–mathematical model of the plasma emitter is presented, in which emission plasma formation conditions in the electrode-expander are considered. On the basis of modelling and experimental research carried out it is shown that electric fields caused by both high working pressure and intensive electron extraction from a plasma can form in the plasma. It is shown that with an increase in critical pressure the electrode-expander goes into the active regime which can be used to increase emission current density with plasma sources development. A double-grid method of emission current stabilization is proposed, which ensures the stability of plasma emitter parameters at high pressures.

This paper reports on the exposure of superhydrophobic polytetrafluoroethylene (PTFE) coatings to common aqueous solutions which are used in biology, biotechnology and chemical sensor applications. Advancing contact angles as high as 173° for aqueous solutions were measured on the PTFE surface. Water drop sliding angles at 2° show a very low contact angle hysteresis. X-ray photoelectron spectroscopy measurements confirm that aqueous solutions can move or stay on the superhydrophobic surface without contamination. Owing to the chemical inertness of the polymer, these results indicate that superhydrophobic PTFE can be used in lab-on-a-chip and multi-sensor devices as well as in biological cultures, where aqueous solutions meet solid surfaces, without contaminating the interface.

This paper is aimed at the determination of the leakage current and the flashover voltage of discontinuously polluted insulators submitted to ac voltages, using a predictive dynamic model based on an equivalent electrical network. This model is an extension of the one we developed for uniformly polluted insulators. The influence of the width and conductivity of polluted layers is investigated. The simulated results are validated experimentally on a plane insulator model using electrolytic solutions of different conductivities.

The electrical conductivity and electrical relaxation for Se–S–In glasses have been reported in the frequency range 0.12–100 KHz and in the temperature range 303–390 K. The enhancement of dc conductivity with increasing indium content has been attributed to the increase in charge carrier mobility. The ac conductivity is found to obey the modified power law σ' = σ_dc + Aω^S + Bω¹. The electrical relaxation is represented in electric modulus formalism. The relaxation dynamic is independent of temperature and shows non-Debye nature.

The transport properties, chemical composition and energy band structure of directly integrated CaRuO_3−δ thin films on a Si substrate were investigated by resistance–temperature (R–T) measurement, x-ray photoelectron spectroscopy (XPS) and near edge x-ray absorption fine structure (NEXAFS) spectroscopy of oxygen K-edge. At high deposition temperatures, the metallic characteristic of CaRuO_3−δ thin film is susceptible, with a clear preference for (1 1 0) crystallite formation, which induces delocalized charge carrier migration. At low deposition temperatures, CaRuO_3−δ thin film takes on semiconductor behaviour responsible for current path localization causing weakening of Ru 4d-O 2p-Ca 3d orbital overlapping due to the imperfect crystalline growth. Even though there was different crystallite formation according to deposition temperature, the relative compositional difference of each element was negligible, which was supported by XPS and wavelength dispersive x-ray spectroscopy (WDXS) analysis. Thus, the change in conductivity from semiconducting to metallic is caused by the fine crystallite nature of CaRuO_3−δ at low deposition temperature which induces charge carrier localization by utilizing the incorporation of Ca–O bonding weakening, reducing the conduction energy bandwidth W and expansion of the local conduction energy band separation Δ.

Polycrystalline BiFe_1−xCr_xO₃ ceramics with x = 0–1 have been produced via a mixed oxide route. The effects of Cr substitution on the structure and on the electrical and ferroelectric properties of BiFe_1−xCr_xO₃ samples have been studied by performing x-ray diffraction, dc resistivity and dielectric measurements as well as characterizing the polarization-field hysteresis loop. The results indicate that the structure of BiFeO₃ can be altered dramatically with a small amount of Cr doping (x = 0.005–0.1). Substitution of Cr for Fe results in large variations in the resistivity of BiFeO₃ ceramics. The resistivity of BiFe_1−xCr_xO₃ samples reaches a maximum value of 2 × 10¹² Ω cm at x = 0.1, which is about two and a half times higher than that for pure BiFeO₃. Doping with 1 mol% Cr increases the dielectric constant and the remnant polarization to four and ten times, respectively, as large as those of a pure sample. There is a strong correlation between the electrical resisitivity, the dielectric constants and the remnant polarization of BiFe_1−xCr_xO₃ ceramics.

Ferroelectric glass–ceramics with a basic composition (1 − y)(Ba_0.70Sr_0.30)TiO₃ : y(BaO : Al₂O₃ : 2SiO₂) have been synthesized by the sol–gel method. The major crystalline phase is the perovskite. The crystallization of the ferroelectric phase in the glass matrix have been studied using differential thermal analysis and x-ray diffraction and the kinetic parameters characterizing the crystallization have been determined using an Arrhenius model. Glass contents ≤ 5 mol% promoted liquid phase sintering, which reduced the sintering temperature to 1250 °C. The dielectric permittivity of the glass–ceramic samples decreased and the ferroelectric–paraelectric phase transition became more diffuse with increasing glass content. The dielectric connectivity of the ferroelectric phase in the composite have also been investigated and are reported.

Thermoelectric properties of substitutional compounds (Zn_0.98M_0.02)₄Sb₃ (M = Al, Ga and In) were investigated at temperatures from 5 to 310 K. The results indicate that substitution of M for Zn in Zn₄Sb₃ leads to a decrease in electrical resistivity ρ, thermopower S and thermal conductivity λ. The decrease in ρ and S of (Zn_0.98M_0.02)₄Sb₃ would originate from increased electron contribution caused by introduction of donor levels due to substitution of M³⁺ for Zn²⁺. Nevertheless, our experiments revealed that as the dopant changed from Al to Ga and then to In, the resistivity of (Zn_0.98M_0.02)₄Sb₃ increased monotonically, which could be caused by reduced mobility due to the increase in the ionic radius from Al to In. Meanwhile, λ of (Zn_0.98M_0.02)₄Sb₃ at low temperatures (especially at T < ∼50 K) decreased continuously as the dopant changed from Al to In, which could be ascribed to the enhancement of phonon scattering by dopants with greater atomic weight. In addition, it was found that the anomalies appearing in the plots of ρ–T and S–T for Zn₄Sb₃ disappeared by doping of either Ga or In, implying that the β to α/α' phase transition of Zn₄Sb₃ was completely prohibited. In particular, the thermoelectric figure of merit of β-(Zn_0.98Al_0.02)₄Sb₃ is found to be larger than that of β-Zn₄Sb₃ at T > 250 K due to the large reduction in its resistivity, indicating that the thermoelectric properties of β-Zn₄Sb₃ can be enhanced by Al doping.

La doped SrBi₂Nb₂O₉ (LSBN) ferroelectric ceramics prepared by the solid-state reaction technique exhibit composition-dependent remanent polarization. X-ray diffraction (XRD) and Raman scattering have been carried out to investigate the effects of La doping on the crystal structure of SrBi₂Nb₂O₉ (SBN). The XRD study shows that the ceramics exhibit increasing preferred c orientation with increasing La content. The results of Raman scattering reveal that the doping La³⁺ ions prefer to replace Sr²⁺ in the A sites of the perovskite blocks (SrNb₂O₇) at a low doping content and they may also occupy the Bi³⁺ sites in the Bi₂O₂ layers with further increasing La content. Accordingly, the observed variation of the ferroelectric properties with the La content in LSBN ceramics can be attributed to the competitive results of La substitution in A sites and Bi³⁺ sites. Our results demonstrate that the ferroelectric properties of La doped SBN are strongly related to the occupied sites of La³⁺ ions.

Ce³⁺ ion doped olgite mineral samples, Na(Sr, Ba)PO₄, were prepared by a high temperature solid-state reaction. The sample was investigated through x-ray powder diffraction, FT-IR and FT-Raman spectra measurements. The optical properties under vacuum ultraviolet (VUV) synchrotron radiation and ultraviolet (UV) irradiation are reported for the first time. The investigated samples show a strong absorption in the VUV and UV ranges. The bands corresponding to the 4f¹ → 4f⁰5d¹ transitions of Ce³⁺ ions in the host lattices are identified. The barycentre of Ce³⁺ ions in the host lattices, the host absorption, the crystal field splitting, the emission and the Stokes shifts are presented and discussed. This Ce³⁺ ion doped material is a potential candidate for plasma display panel (PDP) application.

Piezoelectric ceramics with compositions of (1 − x − y)Pb(Mg_1/3Nb_2/3)O₃–yPbTiO₃–xPbZrO₃ (PMN–PT–PZ), x = 0.025, 0.05, 0.075 and 0.1, close to the morphotropic phase boundary (MPB) were systematically investigated as a function of PT content (y). With increasing PT content, the structures of ceramics in every fixed PZ content series experience a gradual transition process from the rhombohedral to the tetragonal phase near the MPB. Electrical properties such as piezoelectric coefficient (d₃₃), electromechanical factor (k_p), remnant polarization (P_r) and dielectric constant (ε_r) in the respective series all exhibit the peak values corresponding to the structural phase transition near the MPB. Investigations on the temperature dependence of the dielectric constant of (0.95−y)PMN–yPT–0.05PZ ceramics show that an increased Curie temperature T_c and rhombohedral/tetragonal phase transition temperature T_R–T, as well as relatively high electrical properties, can be obtained in some selected compositions. This indicates that the ternary system deserves further exploration for high-temperature applications, especially for the hot research on promising candidates for high-temperature relaxor-based ferroelectric single crystals.

A cavity resonator environment is considered for undulator-generated terahertz radiation pulses interacting repeatedly with a multiple of periodic electron bunches. For synchronization, the bunch period is assumed equal to the round trip time of the radiation pulse. Numerical simulation results along with a small signal analysis are presented.

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