Table of contents

The remarkable phenomenon of weak magnetization hysteresis loops, observed recently deep in the vortex-liquid state of a nearly two-dimensional (2D) superconductor at low temperatures and high magnetic fields, is shown to reflect the existence of an unusual vortex-liquid state, consisting of collectively pinned crystallites of easily sliding vortex chains.

We report and analyse in-plane penetration depth measurements in Y Ba₂Cu₃O_7−δ taken close to the critical temperature T_c. In underdoped Y Ba₂Cu₃O_6.59 we find consistent evidence for charged critical behaviour. Noting that the effective dimensionless charge scales as T_c^−1/2, this new critical behaviour should be generically observable in suitably underdoped cuprates.

The ion implantation technique has been used to fabricate a Co-rich layer in rutile: single-crystalline TiO₂ substrates were heavily irradiated by Co⁺ ions with energy of 40 keV. The magnetic properties of as-prepared and post-annealed samples were studied by both inductive and Faraday magnetometry as well as ferromagnetic resonance (FMR). A ferromagnetic Curie temperature as high as 700 K was measured in our samples. The analysis of the magnetic hysteresis loop, the temperature dependence of the saturation magnetization, and strong out-of-plane anisotropy of the FMR spectra allow us to suppose that the origin of the macroscopic high-temperature ferromagnetism is the exchange interaction mediated by oxygen vacancies.

Measurements on 'free-standing' single-crystal barium titanate capacitors with thickness down to 75 nm show a dielectric response typical of large single crystals, rather than conventional thin films. There is a notable absence of any broadening or temperature shift of the dielectric peak or loss tangent. Peak dielectric constants of are observed, and Curie–Weiss analysis demonstrates first order transformation behaviour. This is in dramatic contrast to results on conventionally deposited thin film capacitor heterostructures, which show large dielectric peak broadening and temperature shifts (e.g. Parker et al 2002 Appl. Phys. Lett. 81 340), as well as an apparent change in the nature of the paraelectric–ferroelectric transition from first to second order. Our data are compatible with a recent model by Bratkovsky and Levanyuk (2004 Preprint cond-mat/0402100), which attributes dielectric peak broadening to gradient terms that will exist in any thin film capacitor heterostructure. The observed recovery of first order transformation behaviour is consistent with the absence of significant substrate clamping in our experiment, as modelled by Pertsev et al (1998 Phys. Rev. Lett.80 1988), and illustrates that the second order behaviour seen in conventionally deposited thin films cannot be attributed to the effects of reduced dimensionality in the system, nor to the influence of an intrinsic universal interfacial capacitance associated with the electrode–ferroelectric interface.

The interplay between clustering and exchange coupling in magnetic semiconductors for the prototype (Ga_1−x,Mn_x)As is investigated considering manganese concentrations x of 1/16 and 1/32, which are in the interesting experimental range. For , we study all possible arrangements of two Mn atoms on the Ga sublattice within a large supercell and find the clustering of Mn atoms at nearest-neighbour Ga sites energetically preferred. As shown by analysis of spin density and projected density of states, this minimum-energy configuration localizes further one hole and reduces the effective charge carrier concentration. Also the exchange coupling constant increases to a value corresponding to lower Mn concentrations with decreasing inter-Mn distance.

Nonhydrodynamic behaviour of charge density autocorrelation functions of molten salts is discussed. It is shown analytically within the three-variable generalized collective modes approach that kinetic propagating charge fluctuations make the contribution to the charge density autocorrelation functions nonvanishing in the long-wavelength limit. A comparison with molecular dynamics results is presented.

We study the dynamics of translational and rotational diffusion during the ageing of a colloidal glass of Laponite using polarized and depolarized dynamic light scattering. The dynamics are qualitatively similar between the two degrees of freedom. The short-time diffusion is independent of the time elapsed since the sample preparation. The intermediate- and long-time diffusion, on the other hand, slows down by several orders of magnitude during the ageing. The slowing down of the rotational diffusion is found to be much faster than that of the translational diffusion.

We review recent advances made in the phase field modelling of polycrystalline solidification. Areas covered include the development of theory from early approaches that allow for only a few crystal orientations, to the latest models relying on a continuous orientation field and a free energy functional that is invariant to the rotation of the laboratory frame. We discuss a variety of phenomena, including homogeneous nucleation and competitive growth of crystalline particles having different crystal orientations, the kinetics of crystallization, grain boundary dynamics, and the formation of complex polycrystalline growth morphologies including disordered ('dizzy') dendrites, spherulites, fractal-like polycrystalline aggregates, etc. Finally, we extend the approach by incorporating walls, and explore phenomena such as heterogeneous nucleation, particle–front interaction, and solidification in confined geometries (in channels or porous media).

We study, in detail, the influence of molecular interactions on the Frank elastic constants of uniaxial nematic liquid crystals composed of molecules of cylindrical symmetry. This work is based on a weighted density functional formalism developed by us in a previous paper (Singh et al 1992 Phys. Rev. A 30 583). A brief summary of the status of theoretical development for the elastic constants of nematics is presented. Considering a pair potential having both repulsive and attractive parts, numerical calculations are reported for three nematics: MBBA, PAA and 8OCB. For these systems the length-to-width ratio x₀ is estimated from the experimentally determined structure of the molecules. The repulsive interaction is represented by a repulsion between hard ellipsoids of revolution (HER) and the attractive potential is represented by the quadrupole and dispersion interactions. From the numerical results we observe that in the density range of nematics the contributions of the quadrupole and dispersion interactions are small as compared to the repulsive HER interaction. The inclusion of attractive interactions reduces the values of elastic constant ratios. The absolute values of elastic constants are sensitive to the values of potential parameters. The elastic constants and their ratios are in agreement with the experimental and computer simulation values. The temperature variation of elastic constants and their ratios are reported and compared with the experimental values. It is found that the calculated values are in agreement with the experimental data. The twist elastic constant has a weak temperature dependence but a pronounced influence is found on the bend elastic constants.

We study the effects of droplet ordering in initial optical transmittance through polymer dispersed liquid crystal (PDLC) films prepared in the presence of an electrical field. The experimental data are interpreted by using a theoretical approach to light scattering in PDLC films that explicitly relates optical transmittance and the order parameters, characterizing both the orientational structures inside bipolar droplets and orientational distribution of the droplets. The theory relies on the Rayleigh–Gans approximation and uses the Percus–Yevick approximation to take into account the effects due to droplet positional correlations.

The conformation of adsorbed polymers is of primary importance for the properties of the generated surface. Theoretical efforts have been made to understand and predict these conformations. In several recent reports, force curves using atomic force microscopy have been proposed as a new tool to probe the conformation of adsorbed polymers through the analysis of the rupture distributions. For a dense polymer layer, many bridges form between the tip and the surface giving highly non-monotonous force profiles. Using recently developed tools for the detection of ruptures and the visualization of the rupture distributions we address the problem of the interpretation of rupture distributions. Two phenomenological constants are deduced and their physical meaning is assessed by varying experimental parameters.

A Rayleigh–Taylor-like interface instability is studied in a compressible Brownian Yukawa fluid mixture on the 'molecular' scales of length and time of the individual particles. As a model, a two-dimensional phase-separated symmetric binary mixture of colloidal particles of type A and B with a fluid–fluid interface separating an A-rich phase from a B-rich phase is investigated, by means of Brownian computer simulations, when brought into non-equilibrium via a constant external driving field which acts differently on the different particles and perpendicular to the interface. Two different scenarios are observed which occur either for high or for low interfacial free energies as compared to the driving force. In the first scenario for high interfacial tension, the critical wavelength λ_c of the unstable interface modes is in good agreement with the classical Rayleigh–Taylor formula provided that dynamically rescaled values for the interfacial tension are used. The wavelength λ_c increases with time, representing an effect of self-healing of the interface due to a local density increase near the interface. The Rayleigh–Taylor formula is confirmed even if λ_c is of the order of a molecular correlation length. In the second scenario for very large driving forces as compared to the interfacial line tensions, on the other hand, the particles penetrate the interface easily due to the driving field and form microscopic lanes with a width different from the predictions of the classical Rayleigh–Taylor formula. The results are of relevance for phase-separating colloidal mixtures in a gravitational or electric field.

A theoretical model is suggested which describes the generation of prismatic misfit dislocation loops surrounding cylindrical quantum dots. These dislocation loops partly accommodate misfit stresses in cylindrical quantum dots embedded in a film deposited onto a substrate. In the framework of the model, the ranges of geometric parameters (misfit parameter f, quantum dot radius a and its height H) are calculated at which the generation of misfit dislocation loops surrounding cylindrical quantum dots is energetically favourable. The exemplary cases of dislocation loop generation in In_xGa_1−xN/GaN and GaN/AlN systems are briefly discussed.

A previously proposed computational procedure for constructing a set of non-orthogonal strongly localized one-electron molecular orbitals (Danyliv and Kantorovich 2004 Phys. Rev. B 70 075113) is applied to a perfect α-quartz crystal characterized by an intermediate type of chemical bonding. The orbitals are constructed by applying various localization methods to canonical Hartree–Fock (HF) orbitals calculated for a succession of finite molecular clusters of increased size with appropriate boundary conditions. The calculated orbitals span the same occupied Fock space as the canonical HF solutions, but have the advantage of reflecting the true chemical nature of the bonding in the system. The applicability of several localization techniques as well as a number of possible choices of localization regions (structure elements) are discussed for this system in detail.

We have studied the problem of phase stability in Fe–Pt and Co–Pt alloy systems. We have used the orbital peeling technique in the conjunction of augmented space recursion based on the tight binding linear orbital method as the method for the calculation of pair interaction energies. In particular, we have generalized our earlier technique to take account of magnetic effects for the cases where the magnetic transition is higher than the order–disorder chemical transition temperature as in the case of Co₃Pt. Our theoretical results obtained within this framework successfully reproduce the experimentally observed trends.

The expansion of the second-generation reactive empirical bond order (REBO) potential for hydrocarbons, as parametrized by Brenner and co-workers, to include oxygen is presented. This involves the explicit inclusion of C–O, H–O, and O–O interactions to the existing C–C, C–H, and H–H interactions in the REBO potential. The details of the expansion, including all parameters, are given. The new, expanded potential is then applied to the study of the structure and chemical stability of several molecules and polymer chains, and to modelling chemical reactions among a series of molecules, within classical molecular dynamics simulations.

A remarkably enhanced yellow–green photoluminescence (PL) was observed from ZnO nanocrystals infiltrated into SiO₂ opal photonic crystals. It was clearly visible to the naked eye under the excitation of an Xe lamp and had substantially improved thermal stability over pure ZnO nanocrystals. The PL spectrum shape of a ZnO–SiO₂ composite opal can be modified by annealing an SiO₂ opal or choosing an SiO₂ opal with different lattice parameters. The enhancement of PL intensity is interpreted based on the dependence of the PL intensity on the size of SiO₂ microspheres as well as the anisotropy of the photoluminescence excitation (PLE) spectra. Our results may be interesting for further application.

The crystal structure of barium–germanium clathrate Ba₆Ge₂₅ was studied using neutron powder diffraction in the temperature range 20–300 K. The compound was found to be cubic (space group P4₁32) in the entire temperature range. However, the fully ordered model of the crystal structure (no split sites) is marginal at room temperature, and clearly fails at low temperature. A much better description of the crystal structure below 250 K is given in terms of two split Ba sites, with random occupancies, for two out of three types of cages present in the Ba₆Ge₂₅ structure. The Ba atoms were found to interact strongly with the Ge host. The separation of the split Ba sites grows with decreasing temperature, with a sudden increase on cooling through the 200–250 K temperature range, accompanied by an expansion of the entire crystal structure. The 'locking-in' of Ba atoms into split sites was originally suggested by Paschen et al (2002 Phys. Rev. B 65 134435) as a plausible scenario behind anomalies in the transport and magnetic properties. Our data prompt us to favour a simple model for this transition, based on temperature-induced de-trapping of Ba from a deep double-well potential. The most significant of the transport anomalies, that is, the drop in electrical conductivity on cooling, can be easily explained within this model through the enhanced structural disorder, which would affect the relaxation time for all portions of the Fermi surface. We suggest that the other anomalies (increase in the absolute value of the negative Seebeck coefficient, decrease in the magnetic susceptibility) can be explained within the framework of the one-electron semi-classical model, without any need to invoke exotic bi-polaron-driven charge carrier interaction mechanisms.

We present a systematic ⁵⁷Fe Mössbauer effect study in the temperature range between 5.3 and 298.2 K and in an external magnetic field of 9.0 T of a high-quality stable decagonal quasicrystal Al₇₀Co₁₅Ni_14.9Fe_0.1. The iron atoms are shown to be located in two distinct classes of sites. The values of the principal component of the electric field gradient tensor and the asymmetry parameter at these sites are, respectively, −1.901(61) × 10²¹ V m⁻², 0.96(12) and −3.927(52) × 10²¹ V m⁻², 0.27(9). The average quadrupole splitting decreases with temperature as T^3/2. The vibrations of the Fe atoms are well described by a Debye model, with the Debye temperature of 546(9) K.

Neutron diffraction, transversal field μSR and magnetization studies of La_1−xSr_xCoO₃ with x = 0.15 and 0.3 has been performed. Long-range ferromagnetic ordering has been found only in the x = 0.3 sample. Magnetization measurements indicate the inhomogeneous magnetic state of this system. Magnetization data confirm well defined long-range ordering for the x = 0.3 sample with , whereas for the x = 0.15 compound this temperature marks the onset of magnetic order within ferromagnetic clusters. μSR data confirm that the transition in the ferromagnetic phase takes place in the large fraction of the x = 0.3 sample, but not in all of the volume. This data also provide evidence for the absence of long-range magnetic ordering for the x = 0.15 sample and show that even short-range ordering takes place only in part of the sample volume. Thus, all these data are in agreement with the phase separation scenario of the concentration phase transition in cobaltites.

Results of the low frequency dielectric constant (ε), dielectric loss and x-ray powder diffraction (XRD) measurements on orthorhombic Al₂(WO₄)₃ under pressure are reported. The dielectric constant and the dielectric loss both show a sharp peak at about 0.5 GPa, indicating a ferroelastic phase transformation. This phase is found to be identical to the low temperature monoclinic phase of Al₂(WO₄)₃. Another monoclinic modification of Al₂(WO₄)₃ is also observed from our XRD studies at 3.4 GPa. Al₂(WO₄)₃ amorphizes above a pressure of 18 GPa, and this pressure induced amorphization is attributed to the lack of thermal activation for decomposition.

This paper is concerned with effective potentials between interacting supramolecular particles separated by a distance R. We focus on the question of why these potentials are typically 'soft', i.e., remain finite for and vary more weakly with R than the underlying interatomic interaction potentials. On the basis of a general expression linking to the free energy of the supramolecular system we investigate the origin of the apparent 'softness' of by considering a number of special model systems, starting with an atom and a diatomic molecule. This simple model already yields a that is finite at R = 0, but does not exhibit the slowly varying character typical of effective potentials for realistic systems. We then show that the larger length scale is recovered when one introduces both many-body interactions and thermal fluctuations within the framework of a 'toy model', that is disc-shaped supramolecular units composed of thermalized configurations of Lennard-Jones atoms. In this case, varies so slowly that it can be parametrized by estimating the free energy change associated with the overlap of the discs. The resulting overlap approximation to behaves qualitatively like ad hoc effective potentials used in mesoscale simulations, such as dissipative particle dynamics. Indeed, on the basis of Monte Carlo simulations and a solution of hypernetted chain integral equations, we find that fluids interacting via DPD and overlap potentials have very similar structural and thermophysical properties. Moreover, the 'overlap' fluid (like other 'effective' fluids) turns out to be so 'soft' that its properties, particularly at high densities, can be very well estimated by a mean-field treatment.

A semiclassical theory for magnetotransport in a quantum Hall system near filling factor ν = 1/2 based on the composite fermion physical picture is used to analyse the effect of local flattening of the composite fermion Fermi surface (CF-FS) upon magnetoacoustic oscillations. We report on calculations of the velocity shift and attenuation of a surface acoustic wave (SAW) which travels above the two-dimensional electron system, and we show that local geometry of the CF-FS could give rise to noticeable changes in the magnitude and phase of the oscillations. We predict these changes will be revealed in experiments, and will be used in further studies of the shape and symmetries of the CF-FS. The main conclusions reported here could be applied to analyse magnetotransport in quantum Hall systems at higher filling factors ν = 3/2 and 5/2 for a Fermi-liquid-like state of the system.

In the local density approximation (LDA) the electronic structure of aluminium is calculated by use of the modified augmented plane wave method (MAPW) self-consistent scheme and the exchange–correlation functional by Vosko, Wilk and Nusair. Since the MAPW scheme produces wavefunctions especially suited for the calculation of the electronic momentum density distribution functions the improper integral defining the Compton profile (CP) J_n(q) in the direction converges well. A comparison with recent measurements of the CP along the principal directions is highly satisfying after Lam–Platzman (LP) corrections are made. In their overall shape the second derivatives of the CPs are found to be in good accord with the experimental results but give in detail no unambiguous information about the signatures of the Fermi surface breaks.

We study the effect of a tilted magnetic field on the orientation of Wigner crystals by taking account of the width of a quantum well in the z-direction. It is found that the cohesive energy of the electronic crystal is always lower for the [110] direction parallel to the in-plane field. In a realistic sample, a domain structure forms in the electronic solid and each domain orients randomly when the magnetic field is normal to the quantum well. As the field is tilted by an angle, the electronic crystal favours alignment along a preferred direction which is determined by the in-plane magnetic field. The orientation stabilization is strengthened for wider quantum wells as well as for larger tilt angles. The possible consequence of the tilted field for the transport property in the electronic solid is discussed.

Phonons in the crystalline phase of 2,-bithiophene (2T) are investigated using the direct method combined with density functional theory (DFT)-based total energy calculations. Phonon calculations are performed as a function of the long range interactions and the displacement amplitude used for calculating Hellmann–Feynman forces. For the first time, we show that both these parameters are crucial in simulating accurately the experimental low-frequency density-of-states of the 2T crystalline phase, obtained from inelastic neutron scattering experiments. The DFT/direct method approach allows the anharmonicity of phonons to be investigated. The anharmonic behaviour of the low-frequency vibrational modes (below 300 cm⁻¹) as the high-frequency vibrational modes at 685, 800 and 885 cm⁻¹ of the 2T crystalline phase is clearly demonstrated. Except for these three latter high-frequency modes, a harmonic behaviour is observed for the intramolecular modes. The calculation of the multiphonon contribution predicts the appearance of a broad background in the 600–1500 cm⁻¹ frequency range, as well as defined features around 950 and 1130 cm⁻¹, in good agreement with the inelastic neutron scattering data. Finally, low-frequency dispersion curves are given.

The x-ray absorption and resonant inelastic x-ray spectra of iron pyrite (FeS₂) have been measured at the S 2p edge and compared with published electronic structure calculations. A minimum in the x-ray absorption intensity interpreted as indicating a gap in the unoccupied density of states is found from about 4 to 6 eV above the bottom of the conduction band, in agreement with some recent calculations. Resonant Raman scattering conditions were set up at the onset of S 2p_3/2 absorption and a constant energy loss peak at 1.9 eV was observed. This is assigned to transitions from occupied t_g to unoccupied e_g states, both of which are predominantly of Fe 3d character but hybridized with the S valence states. This demonstrates that Fe dd excitations can be probed via S 2p resonant spectroscopy, as has been done recently at the O 1s edge for oxide materials.

The intensity of the optically excited 3.1 eV emission from an irradiated feldspar depends on the polarization of the 1.45 eV exciting light, and the 3.1 eV emission is itself polarized. Dipolar transitions are shown to account for the data in both cases. A method is proposed for using the dipole directions deduced from the data to determine the possible lattice sites of the defects in which these optical transitions occur. The method works by assuming the dipole direction will coincide with a symmetry direction of the crystal field around the defect and then checking the crystal structure for sites where this symmetry direction occurs. Two pairs of dipole directions were deduced from the data for both the excitation and the emission, and the directions of one pair aligned close to approximate symmetry axes in the average geometry of the four oxygen anions around the two T1 sites. It is concluded that transitions in defects occupying T1 sites are the most likely explanation for both the excitation and the emission.

Using Mössbauer spectroscopy we have studied stoichiometric and cation deficient LaMnO₃ compounds. The Mössbauer spectra of the stoichiometric LaMnO₃ compound can be interpreted within the cooperative orbital ordered A-antiferromagnetic structure. The cation deficient sample displays spectra which correspond to the orbital 'glass' state without any local signature of Jahn–Teller distorted octahedra.

The compounds Nd₅Si_1.45Ge_2.55 and Pr₅Si_1.5Ge_2.5 have been investigated by means of magnetization measurements and neutron powder diffraction techniques. These alloys present a room-temperature monoclinic Gd₅Si₂Ge₂-type crystallographic structure and, on cooling, both systems order ferromagnetically, at T_C = 56 and 32 K, respectively, from a high-temperature paramagnetic to a low-temperature complex canted ferromagnetic state. The monoclinic crystallographic structure remains unchanged upon cooling down to 4 K, demonstrating the existence of a monoclinic ferromagnetic phase, and the possibility of a full decoupling of magnetic and crystallographic degrees of freedom in the 5:4 lanthanide intermetallic compounds.

Starting from an exact expression for the dynamical spin susceptibility in the time-dependent density functional theory, a controversial issue regarding exchange interaction parameters and spin-wave excitation spectra of itinerant electron ferromagnets is reconsidered. It is shown that the original expressions for exchange integrals based on the magnetic force theorem (Liechtenstein et al 1984 J. Phys. F: Met. Phys.14 L125) are optimal for calculations of the magnon spectrum, whereas the static response function is better described using the 'renormalized' magnetic force theorem given by Bruno (2003 Phys. Rev. Lett.90 087205). This conclusion is confirmed by ab initio calculations for Fe and Ni.

The ferromagnetic (FM) manganite La_0.8Ca_0.2MnO₃ is systematically studied by measurements of internal friction Q⁻¹, Young's modulus E, resistivity ρ and magnetization M versus temperature T. The resistivity ρ(T) exhibits a metal–insulator transition (MIT) at  K. The magnetization M(T) shows a paramagnetic–ferromagnetic (PM–FM) transition at  K and saturates around 182 K. However, the variation of the internal friction with temperature presents a complicated behaviour. In the FM region, three Q⁻¹ peaks at temperatures 98, 143 and 163 K are observed in the spectra of Q⁻¹(T) at the measuring frequency of 1.8 kHz. The origin of three Q⁻¹ peaks is discussed and attributed to the coexistence of metallic and insulating phases in the FM region. In addition, in the magnetic transitional region, the other two peaks at 182 and 244 K at the measuring frequency of 1.8 kHz are observed. Our results indicate that the internal friction method seems to be a useful technique in studying the coupling between spin, charge and lattice of CMR materials.

A quasiparticle method based on a multisite s(p)–d mixing model is used to calculate the exchange constants of dilute magnetic semiconductors (DMS). The effective interaction, which is mediated by s(p) electrons, between d electrons, was taken into account in an effective field approximation or a coherent potential approximation (CPA). The equation-of-motion technique was applied to Green functions to calculate the quasiparticle state density. The exchange constants were calculated in a double-valence-band model, and the microscopic parameter dependences of the exchange constants are investigated for fixed valence band parameters in the model. A ferromagnetic d–d coupling is obtained when the d energy level E_d is in the vicinity of the valence band top, and an antiferromagnetic d–d coupling is obtained when E_d is in the vicinity of the valence band bottom. The maximum of the d–d exchange constant J_{d d}(E_d) increases with the mixing strength. J_{d d} increases with decreasing Fermi energy E_F, and the effect is more significant when E_d approaches the valence band top. J_{d d} also increases with small magnetic impurity concentration x, then reaches a maximum, and finally decreases sharply when x increases further. The quasiparticle state density shows that the ferromagnetism originates from the unsymmetrical broadening of the shallow d energy level in ferromagnetic alignment and related lowering of the centre of gravity of the d state density. Relevant experimental results are discussed on the basis of our calculation.

The SmCo₅ hard magnetic phase was added to magnetoresistive granular Cu–Fe alloys in order to investigate the influence of the presence of a hard magnetic phase on the magnetoresistive properties of a granular alloy that contains a soft magnetic phase. Cu₈₀(Sm_0.17Co_0.83)_xFe_20−x ribbons, with x = 20,15,10,5, obtained by melt spinning, were investigated. The ribbons are composed of magnetic Fe, SmCo₅, and Co precipitates embedded in a Cu matrix. In the as-quenched state, the magnetic interactions between magnetic precipitates lead to the formation of magnetic coherent regions and the magnetoresistance effect is only observed at high field (>1 T). After annealing, the strength of interactions decreases and a magnetoresistance effect is observed at low field (<1 T). The largest magnetoresistance effect (16%) is observed at 5 K for the Cu₈₀(Sm_0.17Co_0.83)₁₀Fe₁₀ alloy annealed at 450 °C.

Studies of dielectric permittivity as a function of the temperature and frequency on Li–Na niobate ceramics in the x = 0–5% Li compositional range have been performed. The results obtained for compositions with have revealed small wide anomalies below the temperature of the main peak corresponding to a ferroelectric (FE) or antiferroelectric (AFE)–paraelectric (PE) or antiferroelectric–antiferroelectric phase transition. The x = 5% Li composition does not show peaks below the temperature of the dielectric constant main peak. The behaviour of the real and imaginary parts of dielectric permittivity of these anomalies as a function of the temperature and measuring frequency together with their Vogel–Fulcher–Tamman like relaxation process gather the characteristics of a relaxor-like behaviour for Li-content compositions, but not in the case of x = 0 composition. The evolution of the Raman spectrum in the 50–180 cm⁻¹ region evidences small structural changes in the 450–560 K temperature interval that indicate the coexistence of two close structural phases with similar energies that should correspond to a ferroelectric Q phase and an antiferroelectric P phase. These obtained results support the assumption of diffusive AFE–FE and FE–AFE phase transitions for x = 0% Li-content and a relaxor-like AFE–FE for content compositions with maxima in the dielectric permittivity in that temperature interval. The results for x = 5% Li-content composition suggest that a single ferroelectric Q-like phase is stabilized. An attempt at a phase diagram is proposed.

SrAlF₅ has been considered as one of the rare fluoride ferroelectric crystals, belonging to the polar I4 group. However, recent x-ray diffraction data suggest that the correct structure is centrosymmetric (I4₁/a). Since ferroelectricity is forbidden in this structure, the existence of an inversion centre was investigated by vibrational spectroscopy. Thus, measurements on SrAlF₅ single crystals have been made by polarized Raman scattering and infrared reflectance spectroscopy. The results, discussed on the basis of the factor group analysis of the proposed structures and other members of the ABF₅ family, favour a centrosymmetric structure.

Two new phosphonium chloroantimonate(III) and chlorobismuthate(III) crystals ([(CH₃)₄P]₃[Sb₂Cl₉] (PCA) and [(CH₃)₄P]₃[Bi₂Cl₉] (PCB)) have been synthesized and their structure determined by means of single-crystal x-ray diffraction. The structure of the title compounds contains discrete [M₂Cl₉]³⁻ anions in general positions and disordered [(CH₃)₄P]⁺ cations. The two compounds are isomorphous in the room temperature phase and crystallize in the polar trigonal space group, P31c. The phase situation in PCA and PCB is established on the basis of differential scanning calorimetry and dilatometric studies. Two phase transitions are found: at 534/534 K () and at 135/138 K () for PCA and at 550/550 K () and at 151/155 K () for PCB (on cooling/heating). The values of the transition entropies (ΔS_tr) obtained suggest that the transitions are of the order–disorder type. The dielectric dispersion measurements have revealed a relaxation process in the PCB crystal. The pyroelectric measurements of both compounds have confirmed the polar nature of the low temperature phase (III). The ferroic (ferroelastic) properties were found over phase III for both crystals.

Polycrystalline samples of R₃Ag₄Sn₄ (R = Pr,Nd) and Nd₃Cu₄Ge₄ intermetallics were studied with magnetometric, x-ray and neutron diffraction methods. All of them crystallize in the orthorhombic Gd₃Cu₄Ge₄-type structure, in which the rare earth atoms occupy two inequivalent crystallographic positions, and order antiferromagnetically below their Néel temperatures of 12 K in the case of Pr₃Ag₄Sn₄, 5 K in the case of Nd₃Ag₄Sn₄ and 4.5 K in the case of Nd₃Cu₄Ge₄. All of the investigated compounds have collinear magnetic structures at low temperatures. In the case of Pr₃Ag₄Sn₄ an additional phase transition to a non-collinear structure is observed. The magnetic structures were studied with the support of group theoretical considerations.

The sulfur K and L_2,3 x-ray absorption near-edge structure (XANES) spectra of FeS, CoS and NiS having the NiAs-type crystal structure have been measured. Theoretical analysis of the experimental data has been conducted by the full multiple-scattering approach. Good agreement between experimental and theoretical data is obtained for comparatively small clusters containing 19–37 atoms. There is no significant difference between S K-edge absorption spectra for the studied compounds calculated by G4XANES and FEFF8.2 packages. The electronic structure of NiS and CoS has been studied by analysing the distribution of calculated electronic states of the sulfides.

Tetraisopropyl titanate (TPT) was mixed with a solution of polyvinylpyrrolidone (PVP) and the solution electrospun into nanofibres. Thermal annealing at 900 °C was used to pyrolyse the PVP, leaving nanofibres of rutile-phase titania. Erbium (III) oxide particles were also added into the solution before electrospinning, and selectively modified the near-infrared optical properties of the titania nanofibres as verified by both absorption and emission spectra. We thereby demonstrate the production of high-temperature optically functionalized nanostructures that can be used in a thermophotovoltaic energy conversion system.