S. N. Kallaev

Thermophysical properties of PLZT ferroelectric ceramics with a nanopolar structure

The heat capacity, thermal expansion coefficient, and deformation of the PLZT-9/65/35 compound are studied in the temperature range 150–800 K. Diffuse anomalies are detected in the temperature dependences of the heat capacity and thermal expansion coefficient over wide temperature ranges of 250–650 and 330–550 K, respectively. The anomalous behavior of the heat capacity in the temperature range 250–650 K is shown to be caused by the appearance of two-level states (Schottky anomaly). The results obtained are discussed along with the data of structural and dielectric studies.

Peculiarities of dielectric properties of nanocrystalline bismuth ferrite

Results of the single-stage synthesis of nanocrystalline bismuth ferrite are presented. It is shown that the temperature and frequency dependences of dielectric properties of specimens produced by the cold compaction of the obtained powder substantially differ from those of microcrystalline bismuth ferrite produced using traditional ceramic technology.

Heat capacity and dielectric properties of multiferroics Bi1 − xGdxFeO3 (x = 0–0.20)

The heat capacity and the permittivity of multiferroics Bi1 − xGdxFeO3 (x = 0, 0.05, 0.10, 0.15, 0.20) have been studied in the temperature range 130–800 K. It has been found that insignificant substitution of gadolinium for bismuth markedly shifts the temperature of antiferromagnetic phase transition and increases the heat capacity over a wide temperature range. It has been shown that the temperature dependence of the excess heat capacity is due to the manifestation of three-level states. Additional anomalies characteristic of the phase transitions have been revealed in the temperature dependences of the heat capacity for the compositions with x = 0.1 and 0.15 at T ≈ 680 K and T ≈ 430 K, respectively. The results of studies of the heat capacity have been discussed simultaneously with the data of structural studies.

Heat capacity of BiFeO3-based multiferroics

The heat capacity of Bi1 − xRexFeO3 (Re = La, Eu, Ho; x = 0, x = 0.05) multiferroics has been studied in the temperature range of 120–800 K. The substitution of a small amount of rare-earth elements for bismuth leads to a significant increase in the heat capacity in the broad temperature range studied. It is established that the temperature dependence of the excess heat capacity is related to the Schottky effect for three-level states certain that appear as a result of structure distortions in the rare-earth-doped compositions.

Heat capacity of nanostructured BaTiO3 ceramics

The temperature dependence of the heat capacity of nanostructured BaTiO3 ceramics produced by the solid-phase method has been studied; before sintering, the synthesized charge is subjected to a severe action in Bridgman anvils in combination with shear deformation. It has been found that the ferroelectric transition is substantially smeared and the phase transition temperature decreases nonlinearly with increasing applied pressure. It has been shown that the defect structure plays a dominant role in the formation of physical properties of the ceramics.

Electrical properties of AgSnSbSe3 under different external effects

The electrical properties of the chalcogenide AgSnSbSe3 have been investigated over a wide range of variations in external parameters, such as the temperature, the pressure, and the frequency of the electric field. It has been found that the temperature dependence of the permittivity and the dependence of the electrical resistivity on the hydrostatic pressure exhibit anomalies that are characteristic of structural phase transitions. The influence of the frequency on dielectric properties of the material has been analyzed.

Effect of heat treatment on the structure and properties of a BiFeO3 nanopowder

This paper presents the results of an investigation of changes in the structure, magnetic, electrical, and thermal properties of a nanostructured bismuth ferrite powder prepared by the combustion of nitrateorganic precursors before and after heat treatment at temperatures of 500, 600, 700, and 800°C. It has been shown that there is a dependence of the magnetic properties on the dispersion of the particles. The specific features of the temperature and frequency dependences of the dielectric properties over wide ranges of frequencies and temperatures, as well as near the Néel temperature, have been considered.

Heat capacity of nanocrystalline bismuth ferrite

The heat capacity of the nanocrystalline multiferroic BiFeO3 was studied in a wide temperature interval of 150–800 K. It was found that the heat capacity nanocrystalline of bismuth ferrite in the temperature range of 350–570 K is noticeably larger than that of the microcrystalline sample. It was shown that the temperature dependence of the excess heat capacity is due to the manifestation of the Schottky effect for the three-level states appearing as a result of the structural distortions. The anomaly of the heat capacity typical for the phase transition, the manifestation of which depends on crystallite sizes, was discovered in the temperature range of T ≈ 720–750 K.

Dielectric properties and specific heat of Bi1–xSmxFeO3 multiferroics

The specific heat and dielectric permittivity of Bi1–xSmxFeO3 (x = 0–0.30) multiferroics have been studied in the temperature range of 300–800 K. A slight substitution of bismuth with samarium is established to cause a considerable shift in the antiferromagnetic phase transition temperature and to an increase in the specific heat over a wide temperature range. Other anomalies typical of phase transitions have been found in the temperature dependences of the specific heat and dielectric permittivity for the compounds with x = 0.10 and 0.15 at T ≈ 735 and 495 K, respectively. The results of the studies of the specific heat have been discussed together with the data of the structural investigations.

Thermal physical properties of ferroelectric ceramics PKR-7M near the diffuse phase transition

The thermal physical properties (heat capacity, thermal expansion coefficient, and deformation) of a relaxor piezoelectric ceramics based on the lead zirconate titanate PKR-7M have been studied in the temperature range 200–800 K. Diffuse anomalies have been revealed in the temperature dependences of the heat capacity and thermal expansion over wide temperature ranges 270–650 and 450–600 K, respectively. It has been shown that the anomalous behavior of the heat capacity is due to the manifestation of two-level states (Schottky anomalies). The results of the study have been discussed together with the data of structural studies.