Synthesis, structure, and electric properties of oxygen-deficient perovskites Ba3In2ZrO8 and Ba4In2Zr2O11

Abstract

Perovskite phases Ba 3 In 2 ZrO 8 and Ba 4 In 2 Zr 2 O 11 with the nominal concentration of structural oxygen vacancies 1/9 and 1/12, respectively, were synthesized by solid-phase and solution methods. X-ray diffraction showed cubic symmetry of both phases with the unit cell parameter a = 0.4193(2) and 0.4204(3) nm, respectively. The absence of superstructural lines resulted in the conclusion on statistical arrangement of oxygen vacancies. Thermogravimetry and mass spectrometry proved that both phases can reversibly absorb water from gas phase ( p H 2 O = 2 × 10 −2 atm) with observed correlation between the concentration of oxygen vacancies and amount of absorbed water. The total water amount was up to 0.9 mol per formula unit or, if recalculated for perovskite unit ABO 3 , 0.3 and 0.23 mol H 2 O, respectively. The temperature curves of coductivity in the atmosphere with various partial water vapor pressures ( p H 2 O = 3 × 10 −5 and 2 × 10 −2 atm) showed significantly higher conductivity and lower activation energy (0.52 eV) in humid atmosphere due to proton transfer. The proton conductivity is up to 5 × 10 −4 Ohm −1 cm −1 at 300°C for Ba 3 In 2 ZrO 8 specimen. IR spectrometry showed that protons in the structure exist primarily in OH-groups.