The electrical conductivity σ of crystals of lithium heptagermanate Li2Ge7O15 doped with Cr and Mn was measured in an alternating-current field with a frequency of 1kHz at 300 to 700K. It was found that doping strongly affects the electrical conductivity. It was established that the addition of 0.1wt%Cr led to an increase in the electrical conductivity σ by almost one order of magnitude, whereas the introduction of 0.03wt%Mn substantially reduces the electrical conductivity along particular crystallographic directions. Data available on the incorporation of Cr and Mn impurity atoms into the lattice suggests that the electrical conductivity was determined by Li ions hopping over interstitial positions along the structural channels.

Ionic Conduction in Li2Ge7O15 Crystals Doped with Cr and Mn Ions. M.P.Trubitsyn, M.D.Volnyanskiĭ, Y.A.H.Obaidat: Physics of the Solid State, 2008, 50[7], 1234-7