Electrical conductivity of superionic conductor single crystals Li$_4$B$_7$O$_{12}$Cl$_{1-x}$Br$_x$ ($x\sim$ 0.3)

The temperature dependence of the ionic conductivity of boracite single crystals Li$_4$B$_7$O$_{12}$Cl$_{1-x}$Br$_x$ ($x\sim$ 0.3, cubic system, space group $F(\bar{43})c)$) has been investigated in the temperature range of 420–738 K. The Li$_4$B$_7$O$_{12}$Cl$_{1-x}$Br$_x$ single crystals have the Li$^+$ ionic conductivity $\sigma$ = 1.1 $\cdot$ 10$^{-2}$ S/cm at 573 K and the ion transport activation energy $E_a$ = 0.49 $\pm$ 0.05 eV. The electrophysical characteristics of the Li$_4$B$_7$O$_{12}$Cl$_{1-x}$Br$_x$ single crystals correspond to the best lithium-conducting solid electrolytes formed in systems with the participation of Li$_2$O and BO$_3$.