Oxygen partial pressure and temperature dependent electrical conductivity of lithium-niobate-tantalate solid solutions

The temperature and oxygen partial pressure (pO2) dependent electrical conductivity of LiNbO3, LiTaO3, LiNb1-xTaxO3 (LNT) solid solutions up to 900 degrees C is presented. The electrical conductivity is found to be isotropic up to about 700 degrees C. Different Nb/Ta ratios do not affect activation energies at temperatures below 600 degrees C, which suggests an identical conduction mechanism, namely the migration of Li ions by means of Li vacancies. Above this temperature, noticeable deviations in the conductivity of Nb rich samples emerge due to strongly increasing electronic contributions. The pO2 dependent conductivity is strongly affected by the Nb/Ta ratio, enabling the tailoring of electrical properties through composition control. At low pO2, Nb rich LNT shows a much larger conductivity compared to LT. At 900 degrees C, conductivity of LT remains unaffected by pO2 down to 10-9 bar. The experimental findings can be understood based on a defect model that does not include the evaporation of Li2O. The latter is, therefore, assumed to play a minor role for the short-term experiments up to 900 degrees C.