Electric conductivity of LiNaGe4O9:Cu crystals

Abstract

Crystals of Li₂O – Na₂O – GeO₂ system belong to the germane-germanates family, in which charge transfer is determined by lithium ionic conduction. Conductivity σ of LiNaGe₄O₉ crystals doped with Cu ions is studied in the paper. Measurements were performed in AC field (f=1 kHz) in the temperature interval 300 – 800 К. It is shown that in contrast to the nominally pure crystals, anisotropy of σ in LiNaGe₄O₉:Cu is practically absent and conductivity has near the same values along three main directions. Activation energy of conductivity in LiNaGe₄O₉:Cu crystals are higher, approximately, one and a half times in comparison with nominally pure samples. Influence of Cu doping on temperature behavior σ(Т) is discussed with the help of EPR spectroscopy data. According to the results of EPR studying, in LiNaGe₄O₉ lattice lithium ions are substituted for bivalent copper centers Cu²⁺®Li⁺. Lithium or sodium vacancies can compensate excess charge introduced by impurity. It is assumed that doping with Cu ions changes mechanism of charge transfer from interstitial to vacancy.