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.
Ceramics of binary systems solid solutions (1x)NaNbO 3-xCa 2 Nb 2 O 7 and (1x)NaNbO 3-xSr 2 Nb 2 O 7 with nonisostructural 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 ¼ 0.1 and x ¼ 0.25). Dielectric characteristics of ceramics revealed the presence of the Maxwell-Wagner polarization and its corresponding relaxation in the solid solutions (1x)NaNbO 3-xCa 2 Nb 2 O 7 at x > 0.20.
The article describes the electrophysical properties research results of the solid solution based on sodium and strontium niobates. The obtained data indicate the preservation of piezoelectric activity in the paraelectric range. The research results will be of interest in the development of diagnostic devices for heat-loaded structures and radio engineering.
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