Ionic conductivity of SrO-Ta2O5 and SrO-La2O3-Ta2O5 compounds
The conductivities of Sr2Ta2O7, Sr3TaO5.5, Sr2LaTaO6 and Sr3LaTa3O12, both doped and undoped, were measured by the ac complex impedance technique over a temperature range of approximately 400–800 °C. The conductivity of Sr2Zr2xTa2 – 2xO7 –x at 800 °C increased from 5.4 × 10–6 S cm–1 for the undoped compound to 3.0 × 10–4 S cm–1 at ×= 0.1, and the activation energy correspondingly decreased from 0.98 to 0.63 eV. Sr3TaO5.5 and Sr2LaTaO6 were found to be the endpoints of a solid solution which can be described by Sr2 +xLa1 –xTaO6 –x/2 where x ranges from 0 to 1. It has the (NH4)3FeF6-type fee structure. There was a maximum in conductivity at x = 0.75 with an oxygen vacancy concentration of 6.25%. The corresponding conductivity at 800 °C was 6.2 × 10–3 S cm–1, nearly identical to 15 % CaO-stabilized ZrO2. The conductivities at 800 °C of Sr2LaTaO6 and Sr3LaTa3O12 were 3.6 × 10–5 and 1.0 × 10–6 S cm–1, and the activation energies over the 400–800°C temperature range were 1.41 and 0.84 eV, respectively.