Vol 80, No 9 (2016)

The structure of the ferroelectric phase of undoped KTiOPO₄ and its solid solutions with zirconium and niobium is studied from first principles within the density functional theory. The second-order nonlinear susceptibility tensor and the spontaneous polarization of these materials are obtained. It is shown that an improvement in nonlinear optical properties of KTiOPO₄ upon doping it with Zr and Nb cannot be explained by a systematic change in the composition of crystals and is apparently associated with the occurrence of defects. Possible structures of such defects are discussed.

Temperature dependences of specific heat C_p(T) and coefficient of thermal expansion ;(T) for Na_0.95Li_0.05NbO₃ sodium-lithium niobate ceramic samples are investigated in the temperature range of 100–800 K. The C_p(T) and α(T) anomalies at T₃ = 310 ± 3 K, T₂ = 630 ± 8 K, and T₁ = 710 ± 10 K are observed, which correspond to the sequence of phase transitions N ↔ Q ↔ S(R) ↔ T2(S). The effect of heat treatment of the samples on the sequence of structural distortions was established. It is demonstrated that annealing of the samples at 603 K leads to splitting of the anomaly corresponding to the phase transition Q → R/S in two anomalies. After sample heating to 800 K, the only anomaly is observed in both the C_p(T) and ;(T) dependence. Possible mechanisms of the observed phenomena are discussed.

The correlation between domain (twin) structures and heterophase states in Ba(Ce_xTi_1–x)O₃ solid solutions near the morphotropic phase boundary is established. The role of individual domains in the formation of structures with two ferroelectric phases is revealed, and the volume concentrations of these phases are calculated for x = 0.02 and x = 0.07 with the complete relaxation of mechanical stresses. The calculated and experimentally determined volume phase concentrations are in good agreement.

Sr_{2 + x}Bi_4–xTi_5–xNb_xO₁₈ materials with x = 0.2, 0.4, 0.6, 0.8, and 1 are synthesized. Investigations of the dielectric constant of the samples reveal an increase in the blurring of the phase transition as the share of titanium ions substituted for niobium ions grows. The Burns temperature and the temperature corresponding to the dielectric permittivity maximum are determined for all of the above compositions. Crossover from a normal ferroelectric to a relaxor ferroelectric in Sr_{2 + x}Bi_4–xTi_5–xNb_xO₁₈ samples is observed.

Low-frequency dielectric losses (tanδ) in barium titanate ceramics with crystallite sizes of ~100 nm near the Curie temperature are studied. It is shown that the observed tanδ maximum is described by a low-frequency fluctuation mechanism of dielectric losses. An analysis of experimental data shows that the critical nucleus size in ultrafine material is smaller than the one in bulk barium titanate.

The properties of six-component ZTS-based ferrosoft ceramic are studied. The ceramic is found to exhibit properties of a ferroelectric relaxor. The R3c → R3m rhombohedral phase transition is observed in the ferroelectric phase of this composite. Polarization of samples with a constant electric field upon cooling through the Curie point enlarges the temperature range of the R3m phase’s existence, compared to roomtemperature polarization.

Linear and nonlinear dielectric properties of KIO₃ polycrystalline samples are investigated. It is shown that linear dielectric permittivity ε' displays four anomalies corresponding to phase transitions in KIO₃. Anomalies of third-harmonic coefficient γ_3ω are observed at temperatures of 113, 263, and 345 K, corresponding to phase transitions between KIO₃ ferroelectric phases. It is established that the third-harmonic coefficient responsible for the nonlinearity of dielectric properties displays no anomalies during the transition to the paraelectric phase of KIO₃ at approximately 485 K. Possible reasons for there being no such anomaly are discussed.

The inverse magnetoelectric effect and internal friction in two-layer composites based on ferromagnetic Tb_0.12Dy_0.2Fe_0.68 and piezoelectric PbZr_0.53Ti_0.47O₃ are studied in an ac electrical field in the frequency range of 52–213 kHz at temperatures of 293 to 400 K. A correlation is found between the internal friction and the efficiency of the inverse magnetoelectric transformation at resonant frequencies.

The dielectric characteristics of film samples of P(VDF-TrFE) + TGS composite in the frequency range of 10³–10⁷ Hz are studied. The values of the real and imaginary parts of the complex dielectric constant in the temperature range of–40 to 140°C, including the points of the polymer matrix’s transition to the glassy state when T_g ≈–25°C and the ferroelectric phase transition. An analysis of the ferroelectric crystal inclusion effect on the dielectric response of P(VDF-TrFE) copolymer matrix is carried out.

Layers of porous silicon (PS), multilayered ZnO films, and heterostructures based on them are obtained. The surface morphology, chemical and phase composition of the PS layers and ZnO films, and the transverse cleavage of ZnO–PS nanocomposite, are investigated via energy-dispersive X-ray spectral analysis (EDX), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The current–voltage characteristics of Al/Ag/p-Si(100)/PS/ZnO/Ag/Al and Al/Ag/p-Si(100)/PS/ZnO/SiC/Ag/Al heterostructures are studied.

A theory of the dynamic properties of surface and bulk polymer structures with dipolar-type order on the level of rigid kinetic units is developed that allows us to establish the relationship between the parameters of inter- and intrachain interactions and the characteristics of orientation order on the one hand, and relaxation properties on the other.

Reaction mixtures in which polymerization processes proceed are investigated both in an electric field and under classical conditions. The observed kinetic effects are explained using a model concept of the primary contribution to the revealed field effects from the dissociation of ion pairs due to the spatial redistribution of ions. This model may be applied to both cationic and anionic polymerization processes.

An approach to the mathematical modeling of elastomer relaxation spectra obtained via acoustic spectroscopy is presented. The solving of Pearson differential equations is the basis for the calculated dependences. The solutions to the equations describe the frequency and temperature distribution of the mechanical loss tangent. The form of the distribution is estimated from selected statistical moments of the experimental relaxation spectra and the mechanical loss tangent.

The effect the conditions of preparing thermoelectric solid solutions of Bi_0.5Sb_1.5Te₃ + 0.06 wt % Pb by hardening from the liquid state with subsequent hot pressing have on their thermoelectric properties is studied. It is found that the optimum thermoelectric quality factors are achieved at a 2200–2800 rpm rate of copper disc rotation.

An approach to estimating the molecular weight distribution function of a polymer in a solution using acoustic spectroscopy data is presented. The estimation function is based on the relationship between relaxation spectra and the molecular weight distribution function, along with the relationship between the relaxation spectra and the frequency distribution of a polymer’s loss modulus.

A method for parametrically predicting the level of non-malfunction work for bipolar integrated circuits under the effects of pulsed gamma neutron radiation with allowance for the relaxation of short-term displacement effects is proposed. The parameters that determine the production margins and radiation sensitivity of parameter U_OL (i.e., the low-level output voltage, the degradation of which generally determines the radiation resistance of bipolar digital integrated circuits) were selected as the ones used in predictions.

The emergence of differences in potential in a natural macromolecular heterogeneous structure (wood) upon natural changes in temperature with allowance for humidity is considered. It is shown that the magnitude of the emerging difference in potential in the wood is proportional to the change in temperature and grows along with the humidity of the wood.

The presence of edge dissipationless currents generated by the emergence of molecular Frenkel excitons in metallophthalocyanine complexes in a constant magnetic field increases the fluorescence intensity for such samples. The consequences of the Frenkel exciton model are discussed from the viewpoint of the observables, which have applications in novel molecular spintronics.

The electric properties of ceramic barium titanate stannate modified with chromium oxide are examined via impedance spectroscopy at frequencies ranging from 100 Hz to 1 MHz and in the temperature interval of 300–550 K. In order to reveal specific electrophysical features of polycrystalline samples that contain crystallites (interior regions of grains) and grain boundaries, a constant electric field that facilitates the accumulation of spatial charge near structural inhomogeneities is applied to the electrodes. The experimental results are interpreted using the Maxwell–Wagner double-layer capacitor model and the Schottky barrier model.

The effect thermal treatment in a vacuum has on the thermoelectric properties of Sb_0.9Bi_1.1Te_2.9Se_0.1 solid solution thin films obtained via ion-beam sputtering in an argon atmosphere is considered. It is established that the specific resistance and thermopower are determined by the type and concentration of intrinsic point defects of the Sb_0.9Bi_1.1Te_2.9Se_0.1 solid solution. The power factor values are found to be comparable to those of nanostructured materials based on (Bi,Sb)₂(Te,Se)₃ solid solutions.