Metastable state of the Li$_2$O–11.5GeO$_2$ glass-ceramics with a high electrical conductivity

A glass of the Li$_2$O–11.5GeO$_2$ composition has been crystallized by heating and isothermal treatment near the devitrification temperature. The thermal properties and electrical conductivity $\sigma$ of the glass in an alternating-current electric field have been investigated in the process of crystallization during the heating. The dependences $\sigma(T)$ have been measured for isothermally crystallized Li$_2$O–11.5GeO$_2$ samples. Glass-ceramic samples in an intermediate metastable state with a high electrical conductivity have been synthesized by heat treatment of the initial glass. At $T\sim$ 500 K, the electrical conductivity of the intermediate state is one order of magnitude higher than that of the initial glass and three orders of magnitude higher than in the case of glass-ceramics consisting of Li$_2$Ge$_7$O$_{15}$ crystallites and the GeO$_2$ amorphous phase. It has been assumed that an increase in the electrical conductivity $\sigma$ of the samples in the intermediate state is caused by the electrical conductivity of subsurface layers and is determined by the presence of a large number of nanometer-scale ordered regions in the structure.