Oleg Ivanov

Diffuse Phase Transition and Ferroelectric Properties of Ceramic Solid Solutions in New SrTiO3-BiScO3 System

Ceramic solid solutions of (1-x)SrTiO3-(x)BiScO3 system with x=0, 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5 have been for the first time synthesized via solid-state processing techniques. Both of end compounds in this system are not ferroelectric materials. X-ray diffraction analysis revealed that at room temperature the samples under study at x=0.2, 0.3, 0.4 and 0.5 consist of mixture of center-symmetric cubic Pm3m phase and polar tetragonal P4mm phase. Anomalous behaviour of dielectric permittivity and dielectric losses for these samples is found to be specific one for ferroelectrics with diffuse phase transitions. Furthermore, examination of the polarization hysteresis behavior revealed weakly nonlinear hysteresis loops in the ferroelectric phase.

Dielectric Relaxation and Ionic Conductivity of a Ceramic System SrTiO3/Y0.1Zr0.9O2

Aceramic material with the composition 0.5SrTiO3—0.5Y0.1Zr0.9O2 was obtained and the characteristics of its dielectric properties and electric conductivity determined. It was found that the material consists of two phases: the cubic Fm3¯m

Physical and technological factors determining Y–ZrO2–Al2O3 composite nanostructured ceramic density

Fm\overline{3}m

Synthesis and properties of the composite ceramics from nanocrystalline Al2O3-30% Y0.1Zr0.9O2 prepared from a water-alcohol solution

phase of yttrium-stabilized zirconium dioxide and the tetragonal I4/mcm phase of the solid solution SrTi1–xZrxO3. Dielectric relaxation with activation energy about 1.1 eV, characteristic for titanium- containing compounds with perovskite structure, was found at temperature T > 500 K. Above ~ 700 K the electric conductivity of the experimental samples increases significantly, which could be due to an increase of the ionic conductivity. The activation energy of electric conduction was about 1.2 eV, which agrees with the value of the activation energy of ionic conduction of zirconium dioxide.

Ferroelectricity in SrTiO3–BiScO3 system

Composite Bi2Te3/SiO2 nanoparticles of the core-shell type have been synthesized for the first time with a view to creating bulk composites possessing high thermoelectric figure of merit (conversion efficiency). It is suggested that bulk composited based on Bi2Te3/SiO2 nanoparticles will provide a combination of low lattice heat conduction due to SiO2 insulator and rather high electric conduction due to charge-carrier tunneling via dielectric spacers between adjacent Bi2Te3 semiconductor grains. The electric resistance of the composite increases with increasing temperature in the range of 130–300 K. This temperature dependence can be described in terms of a tunneling conduction model.

Grain size effect on electrical resistivity of bulk nanograined Bi2Te3 material

The particulars of the sintering process for Y–ZrO2–Al2O3 ceramic materials with different initial structural modifications (tetragonal or cubic) are studied. The effect of cold isostatic compaction on the volume density of such materials sintered at high-temperature is determined.

Enhancement of thermoelectric efficiency in Bi 2 Te 3 via rare earth element doping

A comparative analysis is performed of the microstructural and mechanical particularities of composite ceramic materials obtained from Ce0.1Al0.1Zr0.8O2 nanopowder synthesized by three methods—in the presence of urea, in the presence of hexamethylenetetramine, and using an aqueous solution of ammonia as the main agent. It is established that Ce0.1Al0.1Zr0.8O2 powder synthesized in the presence of hexamethylenetetramine and the ceramic obtained from this powder have superior properties.

Preparation and characterization of bulk composite constructed of Bi2Te3@SiO2 nanoparticles

The hydrogel of the mixed oxide Al2O3-30% Y0.1Zr0.9O2 was prepared by precipitation of ammonia from a water-alcohol mixture (1 : 5). The Al2O3-30% Y0.1Zr0.9O2 compound thus synthesized was characterized using differential scanning calorimetry, transmission electron microscopy, and the BET adsorption method. The obtained sample consisted of spherical particles with an average size of 16–20 nm and a specific surface area of 167 m2/g. The Al2O3-30% Y0.1Zr0.9O2 powder was pressed at 300 MPa and then calcinated at 1600°C for 2 h in air. The topographic and structural features of the prepared ceramics were determined using atomic force microscopy and X-ray electron probe microanalysis. The porosity, the Vickers microhardness, and the tensile strength were determined by mercury porometry.