S. A. Sadykov

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.

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.

Composition, structure, and dielectric properties of SiC-AlN ceramic materials

We have studied the structure, relative dielectric permittivity (ɛ), and dielectric loss tangent (tanδ) of SiC-AlN ceramic materials. The results demonstrate that both ɛ and tanδ are anomalously high in the composition range 30–50 wt % AlN at low frequencies (0.1 kHz). We show that the increase in ɛ may be due to a barrier effect on silicon carbide and aluminum nitride grain boundaries and to migration polarization.

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.

Specific features of the thermal physical properties of relaxor ceramics based on lead zirconate titanate

The heat capacity and thermal expansion of ferroelectric relaxors based on lead zirconate titanate are studied near the diffuse phase transition. It is shown that no spontaneous phase transitions from the paraelectric phase to the ferroelectric phase and from the relaxor state to the normal ferroelectric state occur in an ensemble of nanometer-sized polar regions. It is noted that the transitions can be caused only by external electric fields or storage for a fairly long time.

SWITCHING INDUCED ELECTROLUMINESCENCE IN PZT CERAMICS IN HIGH-VOLTAGE PULSE FIELD

ABSTRACT The luminescence features and internal electronic screening in the ferroelectrics ceramics of PZT system at superfast switching in fast-rising pulse fields are investigated. †Originally presented at 10th European Meeting on Ferroelectricity, Cambridge, UK, August 3–8, 2003.

Reversible polarization of ferroelectric ceramics in a rapid-growing electric field

The complex permittivity of ferroelectric PZT ceramics with different compositions was measured in a pulsed rapid-growing electric field. The time dependence of the real component exhibits three peaks. The dips between them correlate with imaginary component peaks. Domain mechanisms that contribute to the ferroelectric polarization and are responsible for the time dependences are considered.

Structure and Properties of Nanostructured YBa 2 Cu 3 O 7–δ , BiFeO 3 , and Fe 3 O 4

The development of new nanostructured materials based on YBa2Cu3O7–δ, BiFeO3, and Fe3O4 compounds is considered. The structure, morphology, and properties of these materials are studied. The possibilities of fabricating YBa2Cu3O7–δ ceramics with given densities from nanopowders in a single stage by an energy efficient method and growing superconducting films of the same composition on a silicon substrate (on a SiO2 layer) are demonstrated. The technique for fabricating BiFeO3 nanopowder, making it possible to obtain nanostructured ceramics without additional accompanied phases commonly forming during BiFeO3 synthesis is developed. Two methods of the single-stage synthesis of Fe3O4 nanopowder are presented: burning of nitrate-organic precursors and the electrochemical three-electrode method in which one of the electrodes, i.e., an anode containing scrap iron and slurry, is used as an expendable material.