I. N. Andryushina

Phase formation in near-morphotropic region of the PbZr1 − xTixO3 system, structural defects, and electromechanical properties of the solid solutions

Ceramics of PbZr1 − xTixO3 solid solutions were systematically studied in the range 0.37 ≤ x ≤ 0.57. The x-T phase diagram (T = 25°C) is constructed containing in single-phase regions isosymmetric states characterized by different concentration dependences of the structural and electrophysical parameters. There are also regions where these states coexist, with their unit cell volume remaining unchanged. The existence of these states is interpreted in terms of the real (defect) structure of the ceramics. Several reasons are indicated that are responsible for the appearance of the phase states and related to the crystallochemical peculiarities of the solid solutions: the alternate valence of titanium ions; the infinitely adaptive structure of titanium dioxide; and the formation, ordering, and rotation of the planes of crystallographic shear. It is shown that the transition from the rhombohedral to tetragonal phase occurs indirectly, through two intermediate phases with lower symmetry whose appearance is favored by the defects in the solid solutions.

Phase x-T diagram of actual solid solutions of the (1 − x)PbZrO3-xPbTiO3 system (0.37 ≤ x ≤ 0.57)

Ceramics of PbZr1 − xTixO3 solid solutions were systematically studied in the range 0.37 ≤ x ≤0.57. The x-T phase diagram of the system is constructed in the range 25°C ≤ T ≤ 650°C. The diagram has a region of an indefinite symmetry in the vicinity of the transition to the nonpolar cubic phase. It is established that solid solutions in this region are characterized by weak distortions and temperature-time instability of the crystal structure. Three concentration regions are separated differing in the value of the jump in the unit cell volume ΔV at the line of transitions from the rhombohedral (tetragonal) phase to the region of indefinite symmetry. It is revealed that there are three temperature ranges differing in the behavior of the temperature dependence of the inverse permittivity, which are due to the existence of two critical Curie points at the boundary separating the ferroelectric phases from the cubic phase.

Effect of specific features of the phase formation on structural transformations and the formation of properties of solid solutions of the PbZr1 − xTixO3 (0 < x < 1.00) system

The x-T phase diagram (T = 25°C) of the PbZr1 − xTixO3 system has been constructed in the entire solubility range of components 0 ≤ x ≤ 1.00. It has been found that the phase composition of solid solutions, the cell volume decreasing rate, the electrical parameters, and density of ceramics periodically vary with increasing x. It has been shown that the nonmonotonic behavior of the electrical parameters is caused by different contributions of the spontaneous strain dominant in the tetragonal phase and domain reorientations different from 180-degree ones in the rhombohedral phase to their formation. Detailed multifractal parametrization of the grain structure of ceramics has been performed. The microstructure evolution features associated with phase changes in the system have been revealed. The data of other studies that tetragonal phase clusters appear in the range 0.11 < x ≤ 0.12 are confirmed; it has been assumed that rhombohedral phase clusters appear in the range 0.675 < x < 0.80.

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.

Refined phase portrait of the rhombohedral region of the x–T diagram of the Pb(Zr1–xTix)O3 system and singularities of dielectric spectra of its solid solutions

The boundaries of the phase states of solid solutions in the rhombohedral region of the Pb(Zr1‒xTix)O3 (0 ≤ x ≤ 1.00) system and the curve of the R3c → R3m phase transition have been refined on the basis of detailed (with a small concentration step) high-temperature (25°C ≤ T ≤ 700°C) studies of the structural characteristics and frequencies of the piezoelectric resonance of the radial oscillation mode of polarized ceramic samples. It has been shown that, in the range 0.07 ≤ x ≤ 0.20, the transition curve practically coincides with the generally accepted one and, in the interval 0.20 ≤ x ≤ 0.36, it differs from the latter by a nonmonotonic behavior and agrees in the boundaries and regions of the phase states. The curve of the transition from the region of coexistence of the R- and Rh1-phases in the clusterized state to a region with single Rh1-phase in the interval of concentrations 0.08 ≤ x ≤ 0.12 and temperatures 200–250°C has been constructed. The full x–T phase diagram of the Pb(Zr1–x Tix)O3 system has been presented. Dispersion spectra of solid solutions on variation in the frequency of the measuring electric field in the interval of 25–106 Hz have been studied, and their correlation with singularities of the phase portrait has been established.

Phases and morphotropic regions in the PbNb2/3 Mg1/3O3-PbTiO3 system

Ceramic samples of solid solutions (1 − x) PbNb2/3Mg1/3O3 · xPbTiO3 (0 ≤ x ≤ 1.0, Δx = 0.0025–0.05) are prepared by the columbite method. A detailed x−T phase diagram of the system is constructed (isothermal join at 25°C), and dielectric, piezoelectric, and elastic properties are investigated. It is established that the region of the morphotropic phase transition is positioned in the range 0.28 < x ≤ 0.43 and consists of a series of narrower regions. Inside one phase (cubic, rhombohedral, tetragonal), regions are found in which a qualitative and quantitative difference in structural and electrical parameters is observed. An interpretation of the observed effects in the context of the defect structure of the objects is suggested.

Binary, Ternary and Four-Component Systems Based on Sodium Niobate: Phase Diagrams of States, the Role of the Number of Components and Defectiveness in the Formation of the Properties

According to the results of the analysis of the solid solutions in the multicomponent systems, based on lead titanate zirconate (PZT), there have been defined the search stages for the new functional materials for various purposes. The role of the number of components in the formation of the electrophysical properties has been shown. It has been defined that the 5-component systems, based on the PZT, provide the optimal combinations of basic electrical parameters. The phase diagrams of the two-, three- and four-component systems, based on sodium niobate, have been considered. The complexity of phase diagrams has been shown, which are distinguished by a large number of structural transitions, and by a variety of phase transformations in comparison with the systems, based on the PZT. It has been defined that in niobate systems, a considerable growth of electrophysical parameters during the transition to the four-component system was observed. The influence of the defectiveness of solid solutions on the formation of their macroproperties has been revealed. It has been defined that in one multicomponent system, the materials with different totality of the parameters can be obtained on the base of the compounds with fundamentally different macro-responses, which will allow using them in the combined equipment complexes, functioning in a sufficiently wide operating frequency range.

Phase formation and the formation of microstructures and macroscopic responses in BST ceramics

Patterns of phase formation and the formation of microstructure and macroscopic responses in (1–х)BaTiO3–xSrTiO3 (0.00 ≤ х ≤ 1.00) ceramics are established.

Highly Effective Ferroelectric Materials and Technologies for Their Processing

The basis of most commonly ferroelectric ceramic materials (FECMs) used in the modern industry is solid solutions of complex lead oxides. It should be noted that due to significant toxicity of lead compounds there has been an intensive search for alternative materials in recent years. Such efforts resulted from the introduction of a new legislative base aiming at environmental protection [Directive 2002/95/EC of the European Parliament and Council by 27 January 2003 on the restriction of the use of certain hazardous substances in electronic equipment]. In the Research Institute of Physics of SFedU much work has been done for about 30 years to investigate and develop of the environmentally friendly FECMs on the basis of alkali niobate metals. Nowadays such materials are finding more applications in the defense industry rather than other industries. Therefore it is extremely important to promote the production of lead low-cost materials and develop new FECMs.

Dielectric spectroscopy of PbZr1 − xTixO3 solid solutions (0.495 ≤ x ≤ 0.51) in a temperature range of 100-300 K at frequencies from 1 × 10−2 to 2 × 107 Hz

The behavior of the relative permittivity ɛ/ɛ0 of PbZr1 − xTixO3 (PZT) solid solutions (0.495 ≤ x ≤ 0.51) in the temperature range of 100–300 K at frequencies from 1 × 10−2 to 2 × 107 Hz was investigated. Diffuse, strongly relaxing maxima at T = 230−260 K (x = 0.495−0.505) and 150–160 K (x = 0.510) were observed in the PZT studied. The relaxation processes are well described by the Vogel-Fulcher law, and the dielectric spectra are approximated by the Cole-Cole formula.