L. A. Reznichenko

Lead-Free Niobate Ceramics with Relaxor-Like Properties

Ceramics of (1 − x)NaNbO3− (x)Na0.5Bi0.5TiO3 and (1 − x)NaNbO3 − (x)Sr0.5 NbO3 binary solid solutions exhibit strongly diffused permittivity maxima, when x exceeds a threshold value of about 0.15 and 0.1, respectively, but show weak frequency dispersion of permittivity and small frequency shift of the permittivity maximum temperature. Addition of LiNbO3 to these compositions increases the permittivity maximum temperature and greatly enhances the frequency dependence of both the permittivity maximum temperature and permittivity values.

Antiferro-ferroelectric transition in the system (1−x)NaNbO3—xLiNbO3

The dielectric properties of the system (1−x)NaNbO3—xLiNbO3 are investigated. The antiferro-ferroelectric transition region is determined for the first time. It is found that the antiferroelectric phase is stable for x≤0.015, while the ferroelectric phase is stable for x≥0.0225. The transition from one phase to another occurs in the concentration range 0.015

Multifractal properties of grain structures in sodium niobate based binary ceramics with nonisostructural components

The process of grain structure formation and development in ferroelectric ceramics based on sodium noiobate are considered. Micrographs of the grain boundary regions are described in terms of multifractal parameters. Correlations between the multifractal and structural parameters of ferroelectric niobate ceramics are found. The process of secondary interrupted recrystallization has been studied. The results have been used for optimization of the technology of novel ferroelectric materials.

Ferroelectric Elastance of Sodium Niobate-Lithium Niobate Solid Solutions in Relation to A -O Bond Covalence

The ferroelectric elastance of (Na, Li, A0.5′)NbO3 solid solutions was found to vary directly with the total electronegativity of elements A (EN∑A), that is, with the A-O bond covalence at B=const. Using EN∑A values and the position on the phase diagram, one can determine the solid solution parameters optimum for use in high-frequency (A′=Sr, Pb), medium-frequency (A′=Cd), and elevated-temperature (A′=Cd) devices.

A spread in electrophysical parameters of ferroelectric piezoelectric solid solutions and its minimization

A spread in electrophysical parameters of solid solutions based on PZT and niobium oxides is considered for a wide range of component concentration. It is shown that composition fluctuations and their associated solution imperfection cause a significant deviation of the parameters from their mean values. The fluctuations are most pronounced when the crystal structure is unstable (e.g., at morphotropic transitions and near the solubility limits of the components). The optimization of methods for solid solution preparation greatly reduces the effect of process variables on parameter reproducibility.

Highly effective piezoelectric materials for various fields of application

This paper describes highly effective piezoelectric ceramic materials (developed at Rostov State University) which have a combination of parameters required in various fields of application including: materials stable to electrical and mechanical influences; materials possessing high dielectric permittivity; high sensitivity materials; materials possessing high stability of resonance frequency; materials possessing low dielectric permittivity; and high-temperature materials. A number of these materials are used in various industrial devices and instruments. A method for producing novel piezoceramic materials is considered.

Recrystallization of niobate piezoelectric ceramics in the presence of liquid phase

Piezoelectric ceramics of LiNbO3 and LiNbO3-based solid solutions have been sintered from raw materials with different fluorine concentrations. The peculiarities of the structure formation and doping effect on the grain structure are studied. Multifractal parameterization of the ceramics grain structure is per-formed. The possibility of preventing the development of destructive recrystallization in niobate piezoelectric ceramics is shown.

Phase transitions and electrical properties of solid solutions of sodium, lithium, and strontium niobates

An additional study of solid solutions in the (Na, Li, Sr0.5)NbO3 ternary system was performed. More detailed information concerning its phase diagram and physical parameters in a wide range of component concentrations is obtained. The compositions obtained are of interest for application in highly sensitive and high-frequency transducers.

Antiferroelectric-ferroelectric transition in binary systems of solid solutions based on sodium niobate

The dielectric properties of the (1−x)NaNbO3−xKNbO3 and (1− x)NaNbO3−xPbTiO3 systems are investigated. The antiferroelectric-ferroelectric transition regions are determined. It is established that in the (1−x)NaNbO3−xKNbO3 system the antiferroelectric phase is stable for x≤0.01 and the ferroelectric phase is stable for x≥0.0175; the transition from one phase into another occurs in the concentration range 0.01<x<0.0175. In the (1− x)NaNbO3−xPbTiO3 system the transition region lies in the range 0.07<x<0.11.

Influence of phase hardening on transition broadening in a (1−x)NaNbO3−xLiNbO3 system

Dielectric methods are used to study phase-transition broadening in a (1−x)NaNbO3− xLiNbO3 system. It is observed that the lowest values correspond to regions of transition between implanted solid solutions and substitutional solid solutions with 0.05≤x≤0.07. It is shown that the degree of broadening of the phase transition may be varied by phase hardening.