L. A. Reznitchenko

NaNbO3-Based Relaxor

Binary NaNbO3-ABO3 perovskite solid solutions belonging to the group II according to N.N. Krainik classification (Izv. Akad. Nauk SSSR, Ser. Phys. 28, 643 (1964)) exhibit a relaxor-type behavior when the second component concentration exceeds a threshold value x0, corresponding to the abrupt decrease of the dielectric permittivity ϵ maximum temperature Tm. The Tm values of all the known binary NaNbO3-ABO3 relaxor compositions are well below the room temperature and the maximal ϵ values ϵm are much lower than in the case of Pb-containing relaxors. However both Tm and ϵm values may be increased substantially by Li or K-doping leading to the formation of ternary NaNbO3-ABO3-LiNbO3 (KNbO3) solid solutions.

Preisach model and simulation of the converse piezoelectric coefficient in ferroelectric ceramics

The electric-field dependencies of the elastic strains ξ3(E) and the converse piezoelectric coefficients d33(E) for ferroelectric ceramics of different degree of ferroelectric hardness have been measured. The observed results have been approximated by the Preisach and Rayleigh polynomials. The nonmonotonic d33(E) dependence for ferroelectric ceramics has been established. The interpretation of the observed results based on a substantially different distribution of reoriented domains over the internal and coercive electric fields in the ceramics of different degree of ferroelectric hardness is given.

Negative longitudinal electrostriction in polycrystalline ferroelectrics: a nonlinear approach

The longitudinal strains ξ3 of initially unpoled polycrystalline (ceramic) ferroelectrics having different composition were measured as a function of the electric field strength E. The electric field dependences of the longitudinal piezoelectric coefficients d33(E) and longitudinal electrostriction coefficients M33(E) were calculated from the virgin ξ3(E) curves and analysed. It was shown that taking into account the polarization nonlinearity (that is, the dependence of dielectric susceptibility on E) leads to nonmonotonic field dependences d33(E) and M33(E). In a nonlinear system, the electrostrictive effect is due not only to polarization but also to the dependence of dielectric susceptibility on the electric field strength. The large magnitude of the dielectric susceptibility of soft and relaxor ferroelectric ceramics is responsible for the giant electrostriction being positive in low electric fields and negative in strong ones. The possibility of giant negative electrostriction existing has been found for the first time. In strong electric fields, the strain gain has a limitation because of the competition between the positive contribution of the piezoelectric effect and the negative contribution of electrostriction to the strain.

New binary systems of solid solutions based on NaNbO3

The complex investigations of new and known binary systems of solid solutions (SS), based on antiferroelectrics NaNbO3 (NN) with oxides, possessing columbite. KW-bronze, ilmenite and perovskite structure as second components: (1 - x)NN - xAIINb2O6 and (1 - x)NN - xAIITiO3 (AII - Ni. Cu, Mg, Co, Zn, Cd, Mn, Ca, Sr or Pb) have been conducted. The ferro- and piezoelectric properties with a wide range of values have been detected in all systems investigated. There are solid solutions, in which the detected values of electrophysical properties make them suitable for use in piezoelectronics.

Atomic substitution effects in binary solid solution systems based upon NaNbO3

Several regular variations of electrophysical properties, which depend on substituting atoms characteristics, have been found by the use of computed and experimental characteristics of interatomic A-O and B-O bonds of solid solutions in binary systems of two types: NaNbO3-A0.5IINbO3(ANb2O6) and NaNbO3-AIITiO3) where AII = Ni, Cu, Mg, Co, Zn, Mn, Cd, Ca, (NaBi)0.5, (AgBi)0.5, Sr, (KBi)0.5, Pb or Ba. The correlations between Curie temperature, Tc, dielectric permittivity, ∊33T/∊0, piezocoefficient, d31, electromechanical coupling factor, Kp, on one hand and interatomic bond lengths A-O and B-O on the other hand have been determined.

Comparative Dielectric Studies of NaNbO3–Based Lead-Free Relaxor Ceramics and Lead-Containing Relaxors

Complex dielectric permittivity ϵ* = ϵ′ -iϵ″ of lead-free (Na, Sr, Li)NbO3 ceramic composition exhibiting a relaxor-like dielectric behavior was studied in wide temperature (−180–500°C) and frequency (10 2 –10 6 Hz) range. Some features characteristic of relaxors were observed, namely fulfilment of quadratic and linear Curie-Weiss laws for ϵ ′ just above and well above the temperature T m of ϵ′ (T) peak respectively, the Vogel-Fulcher scaling of both ϵ′ (T) and ϵ” (T) peaks. However, in contrast to canonical lead-containing relaxors Curie-Weiss temperature is lower than T m and the scaling parameters differ for ϵ′ (T) and ϵ”(T) suggesting different origin of dielectric relaxation in these two groups of materials.

Correlation between the microstructure of ferroelectric ceramics and their chemical and phase composition, the degree of perfection of the crystal structure and the preparation conditions

The correlation between crystallite sizes of ferroelectric ceramics and spontaneous deformation of the crystal unit cell was considered for two cases: 1) in varying concentrations of solid solutions of the systems based on NaNbO3 and PbTiO3-PbZrO3, and 2) in the individual compositions of the above systems with the crystallite size varying with the preparation conditions. It is shown that in the first case there is a reciprocal dependence between the homogeneous deformation parameter Δ characterizing the spontaneous deformation of the crystal unit cell and the crystallite sizes d. In the second case Δ varies with d.

Some Properties of the Relaxor-Like Behavior in Sodium Niobate-Based Binary Solid Solutions

Some crystallochemical regularities of the appearance of relaxor-like dielectric behavior in binary (1-x)NaNbO 3 -(x)ABO 3 solid solutions have been revealed. The most significant frequency shift of permittivity maximum temperature T m is observed for solid solutions, where the aliovalent ion substitutions take place in both cationic sublattices of NaNbO 3 , or for solid solutions, where the difference in the valency of the dopant and host ions exceeds unity. A linear correlation between the frequency shift of T m and the parameter δ of the permittivity maximum diffusion was revealed.

Secondary discontinuous recrystallization as a manifestation of the effect of self-organization in niobate ferroelectric ceramics

The use of a synergetic approach in interpreting the results of experimental investigations of micro-structure of ferroelectric ceramics based on niobates of alkali metals is discussed. The observed effect of a secondary discontinuous recrystallization is considered in terms of self-organization. It was established that by varying technological conditions one could eliminate this phenomenon from the process of recrystallization of the niobate ferroelectric ceramics and, thereby, improve their properties.

Phase diagrams and ferroelectric properties of solid solutions of the ternary systems (Na, Li, Cd0.5)NbO3 AND (Na, Li, Sr0.5)NbO3

Some precision X-ray studies of solid solutions of the ternary systems (Na, Li, Cd0.5)NbO3 and (Na, Li, Sr0.5)NbO3 were carried out, which enabled one to determine more accurately the symmetry of crystallizing phases, structural transitions and the morphology of morphotropic regions. Concentration dependences of electrophysical characteristics of solid solutions of these systems were studied and their relation with structural parameters was revealed.