Li+ ion conductivity and transport properties of LiYP2O7 compound

A lithium yttrium diphosphate LiYP2O7 was prepared by a solid-state reaction method. Rietveld refinement of the X-ray diffraction pattern suggests the formation of the single phase desired compound with monoclinic structure at room temperature. The infrared and Raman spectrum of this compound was interpreted on the basis of P2O74- vibrations. The AC conductivity was measured in the frequency range from 100 to 10(6) Hz and temperatures between 473 and 673 K using impedance spectroscopy technique. The obtained results were analyzed by fitting the experimental data to the equivalent circuit model. The Cole-Cole diagram determined complex impedance for different temperatures. The angular frequency dependence of the AC conductivity is found to obey Jonscher's relation. The temperature dependence of sigma(AC) could be described in terms of Arrhenius relation with two activation energies, 0.87 eV in region I and 1.36 eV in region II. The study of temperature variation of the exponent(s) reveals two conduction models: the AC conduction dependence upon temperature is governed by the correlated barrier hopping (CBH) model in region I (T < 540 K) and non-overlapping small polaron tunneling (NSPT) model in region II (T > 540 K). The near value of activation energies obtained from the equivalent circuit and DC conductivity confirms that the transport is through ion hopping mechanism dominated by the motion of the Li+ ion in the structure of the investigated material.