AC conductivity scaling behavior in grain and grain boundary response regime of fast lithium ionic conductors

AC conductivity spectra of Li-analogues NASICON-type Li1.5Al0.5Ge1.5P3O12 (LAGP), Li–Al–Ti–P–O (LATP) glass–ceramics and garnet-type Li7La2Ta2O13 (LLTO) ceramic are analyzed by universal power law and Summerfield scaling approaches. The activation energies and pre-exponential factors of total and grain conductivities are following the Meyer–Neldel (M-N) rule for NASICON-type materials. However, the garnet-type LLTO material deviates from the M-N rule line of NASICON-type materials. The frequency- and temperature-dependent conductivity spectra of LAGP and LLTO are superimposed by Summerfield scaling. The scaled conductivity curves of LATP are not superimposed at the grain boundary response region. The superimposed conductivity curves are observed at cross-over frequencies of grain boundary response region for LATP by incorporating the $$ \exp \left( {{{ - (E_{A}^{t} - E_{A}^{g} )} \mathord{\left/ {\vphantom {{ - (E_{A}^{t} - E_{A}^{g} )} {kT}}} \right. \kern-0pt} {kT}}} \right) $$ factor along with Summerfield scaling factors on the frequency axis, where $$ E_{A}^{t} $$ and $$ E_{A}^{g} $$ are the activation energies of total and grain conductivities, respectively.