AC IMPEDANCE STUDIES OF GLASSY AND CRYSTALLINE LITHIUM ALUMINOSILICATE COMPOUNDS

A.C. impedance spectroscopy was used to characterise the electrical conductivity behaviour of polycrystalline beta-LiAlSi2O6, beta-LiAlSiO4 and the corresponding glasses with identical stoichiometric compositions. Two bulk conduction processes with different activation energies were detected for beta-LiAlSiO4. The dispersion in the conductivity of the samples, the non-Debye conductivity relaxation and the frequency dependence of the a.c. activation energies are discussed. The problem of how best to compare data from impedance measurements with results obtained from NMR relaxation experiments is addressed. It was found that diagrams of log resistivity against reciprocal temperature, plotted for individual frequencies, are suitable for comparing directly with NMR data.