Phase states, microstructure and dielectric characteristics of solid solutions (1 - x)NaNbO3 - xCa2Nb2O7 and (1 - x)NaNbO3 - xSr2Nb2O7.

Ceramics of binary systems solid solutions (1 - x)NaNbO3 - xCa2Nb2O7 and (1 - x)NaNbO3 - xSr2Nb2O7 with non-isostructural extreme components were prepared by the solid-phase reactions technique with the following sintering using conventional ceramic technology. It was found that ceramics with x ≤ 0.2 have a perovskite structure. Layered type of structure predominates in the concentration range 0.2 < x ≤ 1. Phase diagrams of both systems at room temperature have been determined in the perovskite area. It was shown that this area contains two concentration regions with the different crystal structures and the morphotropic phase boundary between them. Microstructure and dielectric characteristics of selected solid solutions were investigated. The influence of technological regulations, such as mechanical activation and variation of sintering temperatures, on the formation of the microstructure and dielectric characteristics was studied for the individually selected concentrations (x = 0.1 and x = 0.25). Dielectric characteristics of ceramics revealed the presence of the Maxwell-Wagner polarization and its corresponding relaxation in the solid solutions (1 - x)NaNbO3 - xCa2Nb2O7 at x > 0.20.

Multi-element ferroactive materials based on KNN-PZT compositions with fundamentally different physical properties.

Quasibinary section solid solutions of a four-component system of the (1-x)(Na0.5K0.5)NbO3-xPb(Ti0.5Zr0.5)O3 composition, based on compositions with fundamentally different physical responses (Na, K)NbO3(KNN), Pb(Ti, Zr)O3 (PZT), have been produced by two-step solid-phase synthesis followed by sintering using conventional ceramic technology. The features of their structural formation have been revealed, a phase diagram of equilibria has been constructed, correlation relationships composition ‒ structure ‒ microstructure ‒ macroproperties have been established. Based on the measured X-ray fluorescence intensities, the concentrations of chemical elements, included in the surface composition of the samples of piezoceramic materials, have been determined. Statistical characteristics and variations in the chemical composition of the structure-forming chemical elements of the ferroactive composite materials were researched. Micro-XRF combined with methods of mathematical statistics provides to characterize a degree of chemical homogeneity and statistically compare the average concentrations of the chemical elements. Changes in atomic concentrations were revealed as result of varying technological conditions of synthesis. We have carried out the X-ray quantitative analysis for the thickness of surface layer corresponding to the chemical elements at the depth yield of X-ray fluorescence. Three groups of solid solutions ‒ the foundations of intelligent materials have been identified: with high K p , ε 33 T/ε 0 low V 1 E (near PZT) - promising for low-frequency applications; with low ε 33 T/ε0, high V 1 E (near KNN) ‒ for high-frequency use; with intermediate values of the piezoelectric parameters (near SS1→SS2 ‒ transition), intended for operation in combined equipment complexes.

Intercalation of water molecules from the air into perovskite and layered structures formed in the system of NaNbO3-Ca2Nb2O7.

The study results of the perovskite solid solution and layered compounds formed in the system of (1-х)NaNbO3-xCa2Nb2O7, x = 0.10, 0.25, 0.55, 1.00 are presented. The objects of the study are obtained by solid-phase synthesis, followed by sintering using conventional ceramic technology. The study of dielectric spectra has revealed their anomalous behavior in the temperature range of 360-450 K, most pronounced in the composition with x = 0.25. To explain the anomalies in these objects, a microstructural analysis of ceramics, thermogravimetry, high-temperature powder X-ray diffraction, and IR spectroscopy heve been performed. It has been established that the anomalies of the dielectric spectra in the indicated range are due to the adsorption of water from the air, its dissociation and the incorporation of the OH2 and OH- oxyhydryl groups into the crystal lattice of the solid solution and the compounds. In a compound located near the boundary between solid solutions and layered compounds, the process of water adsorption is accompanied by the appearance of an intermediate incommensurate phase and ends with the formation of a new compound.