Origin of Constant Loss in Ionic Conductors

Abstract

We have analyzed the constant loss contribution to the ac conductivity in the frequency range 10 Hz–1 MHz and temperatures down to 8 K, for two Li ionic conductors, one crystalline ( ${\mathrm{Li}}_{0.18}{\mathrm{La}}_{0.61}{\mathrm{TiO}}_3$) and the other glassy ( $61{\mathrm{SiO}}_2̇35{\mathrm{Li}}_2\mathrm{O}̇3{\mathrm{Al}}_2{\mathrm{O}}_3̇{\mathrm{P}}_2{\mathrm{O}}_5$). As temperature is increased a crossover is observed from a nearly constant loss to a fractional power law frequency dependence of the ac conductivity. At any fixed frequency $\omega$, this crossover occurs at a temperature $T$ such that $\omega \approx {\nu }_0\exp \left({-E}_m/k_{B}T\right)$, where ${\nu }_0$ is the attempt frequency and $E_m$ is identified with the barrier for ${\mathrm{Li}}^{+}$ ions to leave their wells.