I. A. Verbenko

Effect of sintering temperature on the density, piezodielectric response, and mechanical and elastic properties of materials of different functional groups

This paper describes the synthesis of Ba-doped PbZn1/3Nb2/3O3-PbMg1/3Nb2/3O3-PbNi1/3Nb2/3O3-PbTiO3 multicomponent solid solutions rich in PbNi1/3Nb2/3O3, which include ferroelectric relaxors, ferroelectrics with a diffuse phase transition, and classic ferroelectrics, and presents the phase diagrams along three cuts through a section near PbNi1/3Nb2/3O3. We examine the effect of sintering temperature on the density, piezodielectric response, and mechanical and elastic properties of ceramics of different functional groups; optimize the conditions for the fabrication of such ceramics, and compare the performance parameters of the materials obtained with those of their commercially available analogs.

Microstructure and dielectric and piezoelectric properties of PbFe0.5Nb0.5O3 ceramics modified with Li2CO3 and MnO2

Unmodified lead ferroniobate (PFN) and samples modified with 1 wt % Li2CO3 (PFNL) and 1 wt % MnO2 (PFNM) have been prepared by solid-state reactions followed by sintering by a conventional ceramic processing technique. The modifiers have been shown to change the nature of the recrystallization sintering process, reduce the optimal sintering temperature of the material, increase its average grain size, stabilize its dielectric properties, and improve its piezoelectric performance. The observed effects are interpreted in terms of the crystal-chemical specifics of the modifiers and their location in the structure of the parent compound.

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.

Synthesis, structure, and optical characteristics of barium–strontium niobate thin films

Films of the Ba0.5Sr0.5Nb2O6 (BSN) solid solution on the MgO(001) substrate were fabricated by high-frequency RF sputtering in oxygen. Optical spectra of discharge glow when sputtering the BSN ceramic target and the structure and optical characteristics of BSN/MgO(001) films at room temperature were investigated. It was shown that the BSN films grow from a dispersed phase in the discharge gap, while their growth rate with the used deposition mode at the initial stage is 8–9 nm/min. It was established that the grown films are single-crystal, contain twins, and film surfaces are parallel to the crystallographic planes (001). The angle, at which the reflection intensity is independent of the film thickness, was found in the family of specular reflection curves of H-polarized radiation with wavelengths of 500–800 nm from the films under study at room temperature. The tangent of this angle is equal to the refractive index of the film material, while its presence indicates the identity of optical characteristics of the film material of different thicknesses and low roughness of their surfaces.

The crystal and grain structure and physical properties of Bi1 − xAxFeO3 (A = La, Nd) solid solutions

High-quality ceramics were synthesized on the basis of Bi1 − xAxFeO3 (A = La, Nd; 0.00 ≤ x ≤ 0.20) solid solutions. Their crystal and grain structure, Mössbauer spectra, and other dielectric and magnetic characteristics were studied. It was shown that an increase in the content of A elements in the studied samples considerably enhanced their magnetic susceptibility and magnetoelectric effect.

Optimizing conditions of fabrication and the properties of BaNb2O6-SrNb2O6 binary ceramics

Conditions for fabricating (Ba0.5Sr0.5)Nb2O6 ceramics are optimized. It is shown that materials synthesized at T = 1250°C and sintered at T = 1375–21400°C exhibit the best ceramic characteristics. The (Ba0.5Sr0.5)Nb2O6 solid solution is found to be a ferroelectric with a diffuse phase transition. The possibility of fabricating Ba0.5Sr0.5Nb2O6 thin films from ceramic targets prepared in the resulting optimum regimes is shown.

Phase diagram of the system of (1–х)BiFeO3–xPbFe0.5Nb0.5O3 solid solutions at room temperature

Experimental samples of solid solutions of the (1–x)BiFeO3–xPbFe0.5Nb0.5O3 (0.00 ≤ x ≤ 1.00, Δx = 0.025–0.05) system have been prepared according to the conventional ceramic technology. Their structural and dielectric characteristics have been studied. A phase diagram of the system at room temperature has been plotted taking into account the crystallochemical specificity, spatial inhomogeneity, and structural imperfection of the samples. This diagram is characterized by the presence of solid substitutional and interstitial solutions; the formation of concentration ranges with a dominant role of BiFeO3 and PbFe0.5Nb0.5O3; the presence of five single-phase regions, two regions of coexistence of phase states, and three morphotropic regions; and the formation of six regions with a constant experimental unit-cell volume. Correlations between the structural characteristics and dielectric properties of the ceramics under study have been established.

Granular structure and dielectric characteristics of the (Ba0.5Sr0.5)Nb2O6 ceramics

The granular structure and the dielectric characteristics of the ceramic (Ba0.5Sr0.5)Nb2O6 solid solution are studied. The ceramic is found to be characterized by a homogeneous, dense, almost pore-free microstructure consisting of crystallites 5–10 µm in size. At room temperature, (Ba0.5Sr0.5)Nb2O6 exhibits elongated hysteresis loops. The ceramic undergoes a diffuse phase transition from a paraelectric state into the state of relaxor ferroelectric in the temperature range T = 340–385 K upon cooling. Scaling is shown to weakly change the ceramic characteristics of the material.

Phase equilibrium and properties of solid solutions of PbTiO3-PbZrO3-PbNb2/3Mg1/3O3-PbGeO3 system

Phase diagrams of three sections of the four-component system PbTiO3-PbZrO3-PbNb2/3Mg1/3O3-PbGeO3 are plotted (at 20°C) and electrophysical properties of solid solutions are studied. It is found that morphotropic areas, in which dielectric, piezoelectric, and elastic properties are extreme, have a wider concentration interval than in binary systems serving as the base for the studied solid solutions. In monophase areas, isosymmetrical fields (phase states) divided by areas of constant structural parameters are revealed. An explanation of the observed effects based on the real defect structure of objects is proposed.

Effect of lithium carbonate on the ferroelectric properties of lead ferroniobate ceramics

We have studied the grain and crystal structures and the dielectric (300–700 K) and piezoelectric characteristics of ceramic samples of unmodified multiferroic lead ferroniobate and materials modified with lithium carbonate above stoichiometry during synthesis. The addition of the modifier has been shown to improve the microstructure of the samples, increase their resistivity, improve their dielectric controllability, and raise their piezoelectric activity. The observed effects have been tentatively attributed to the formation of Li-containing liquid phases during synthesis of the material and to partial Li cation incorporation into the crystal structure of the host compound. The optimal modifier concentration is 1–2 wt %.