Ion conduction and space-charge polarization processes in Li2Ge7O15 crystals

The electrical properties of a lithium heptagermanate (Li₂Ge₇O₁₅) crystal have been studied in DC and AC measuring fields at temperatures from 500 to 700 K. In a DC field, a substantial decrease of electrical conductivity σ with time has been detected. On the basis of kinetic dependences σ(t), estimates of the charge carrier diffusion coefficient D have been obtained. In the frequency range 10¹–10⁵ Hz, the spectra of complex impedance ρ*(f) have been measured. The analysis of diagrams in the complex plane (ρ″–ρ′) has been performed within the equivalent circuit approach. It has been shown that, in the considered temperature and frequency intervals, the electrical properties of Li₂Ge₇O₁₅ crystals have been determined by the hopping conduction of interstitial lithium ions A _Li and accumulation of charge carriers near the blocking Pt electrodes.