Ceramic solid solutions of Li$_{0.17}$Na$_{0.83}$Ta$_{y}$Nb$_{1-y}$O$_{3}$: thermobaric synthesis, microstructure, and properties

Ferroelectric ceramic Li$_{x}$Na$_{1-x}$Ta$_{y}$Nb$_{1-y}$O$_{3}$: ($x$ = 0.17, $y$ = 0 – 0.5) solid solutions with perovskite structure are synthesized for the first time by the thermobaric synthesis method (6 GPa, 1400 – 1800 K). The features of their structure and elastic properties are studied. It is shown that ceramic samples consist of grains of isomorphic shape and that faceting is inherent in the perovskite structure, allowing the coexistence of the rhombic phase of different symmetries of the $P$21$ma$ and $Pbcm$ unit cell. An increase in the synthesis temperature leads to a decrease in the Young's modulus. The dispersion of the permittivity and its temperature dependence are studied. Specific static values of electrical conductivity and their temperature dependence, as well as the most probable relaxation time, are determined. Carrier activation enthalpies $H_a$ and transport enthalpy $H_m$ are calculated. It is established that the studied ceramic samples undergo a ferroelectric phase transition, while an increase in tantalum concentration lowers the Curie temperature. Li$_{0.17}$Na$_{0.83}$Та$_{0.1}$Nb$_{0.9}$O$_{3}$ in the paraelectric phase is found to be a superionic conductor.