Ionic and Polaronic Conductivity of Lithium Niobate.

Ceramics of lithium niobate with different lithium-to-niobium ratios were studied by impedance spectroscopy in the 1 Hz to 13 MHz frequency range and the 300–1000 °C temperature range. The static conductivity was determined for all compositions from Cole-Cole diagrams, and the evolution versus temperature was studied as a function of the Li/Nb ratios. The evolution of the ionic conductivity as a function of the temperature showed a change of slope at a temperature threshold. This change of slope may have been related to a modification of the conduction mechanism. At first, the mechanism followed a polaronic conduction model before the temperature threshold with an average activation energy of 0.84 eV; then it followed an ionic model after the temperature threshold, with an average activation energy of 1.20 eV. [ABSTRACT FROM PUBLISHER]