50 mol% indium substituted BaTiO3: Characterization of structure and conductivity

BaTi0.5In0.5O3−δ was prepared by solid state reaction at 1400 °C. Rietveld analysis of high resolution X-ray powder diffraction data indicated phase pure as-prepared material that adopts a cubic perovskite structure with a = 4.1536(1) Å. Thermogravimetric analysis revealed the presence of significant levels of protons in the as-prepared material and 57% of the theoretically achievable protonation was attained on exposure to a humid environment at 185 °C. After hydration the cell parameter increased to 4.1623(1) Å. Electrical conductivity was measured both with fixed and variable frequency ac impedance methods as a function of temperature, oxygen-, water vapour- and heavy water vapour partial pressures. In the temperature range 400–800 °C a slight increase in the total conductivity with increasing oxygen partial pressure is encountered, characteristic of a contribution from p-type charge carriers. The effect of the water vapour pressure on conductivity below 600 °C is much more prominent indicative of dominant proton conduction. At 300 °C the total conductivity in wet O2 was estimated to be 9.30 × 10−5 S/cm. At T > 800 °C the material is a pure oxide ion conductor.

► BaTi0.5In0.5O3−δ is investigated as a solid state electrolyte. ► Thermogravimetric analysis reveals high level of protonation is possible. ► Conductivity measured as function of temperature, oxygen and water vapour partial pressure. ► Proton conduction dominates at T < 500 °C, oxide ion at T > 600 °C. ► p-type contribution observed at intermediate temperatures.