Synthesis and electrochemical properties of Li$_{8-x}$Zr$_{1-x}$Nb$_x$O$_6$ solid solutions

New lithium-conducting solid solutions based on lithium orthozirconate have been synthesized by mutual doping of the related structures Li$_8$ZrO$_6$ and Li$_7$NbO$_6$. The main factor determining the increase in the electrical conductivity of the Li$_{8-x}$Zr$_{1-x}$Nb$_x$O$_6$ solid solutions is the formation of lithium vacancies in the tetrahedral and octahedral layers. The practical stability of the Li$_{8-x}$Zr$_{1-x}$Nb$_x$O$_6$ ceramics to metallic lithium has been studied.