Z. M. Omarov

Specific features of the thermal, magnetic, and dielectric properties of multiferroics BiFeO3 and Bi0.95La0.05FeO3

Thermophysical, magnetic, and dielectric properties of multiferroic BiFeO3 and Bi0.95La0.05FeO3 ceramic compounds were comprehensively studied. Anomalies of the permittivity near an antiferromagnetic phase transition related to the structural variations were detected. The temperature TN was determined from the temperature dependences of the thermal expansion coefficient, heat capacity, and differential susceptibility. It is shown that the transition point is shifted to higher temperatures as the rare-earth La ion substitutes for Bi. It is established that an insignificant substitution of lanthanum for bismuth enhances the magnetic properties of bismuth ferrite and the magnetodielectric effect.

Thermal and Electrical Properties of Gadolinium Sulfides at High Temperatures

A study is made into the temperature dependence of the thermal conductivity, electrical conductivity, thermoelectromotive force, thermal expansion coefficient, and heat capacity in the temperature range from 300 to 1200 K for polycrystalline gadolinium sulfides GdSy(y= 1.495–1.487) produced both by recrystallization pressing and by crystallization from a melt. The role of the mechanisms of heat and charge transfer is estimated depending on the composition. The reasons for changes in their electrical and thermal properties are analyzed. The thermoelectric efficiency is calculated. It is demonstrated that Z≥ 0.6 × 10–3K–1at T≥ 1000 K.

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.

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.

Phase transformations and properties of Ag1 − yNbO3 − y/2 (0 ≤ y ≤ 0.20) ceramics

We have studied the phase transformations, microstructure, and dielectric, piezoelectric, and thermophysical properties of Ag1 − yNbO3 − y/2 (0 ≤ y ≤ 0.20) ceramics. Within its homogeneity range (y ≤ 0.10), silver niobate undergoes a complex sequence of phase transformations, accompanied by anomalies in its physical properties. The observed dispersion effects are interpreted in terms of electrical conductivity above the Curie temperature and in terms of the motion of domain walls and interfaces below the Curie temperature.

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.

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.