A-site deficient perovskite-type compounds in the ternary CaTiO3-LaCrO3-La2/3TiO3 system

Phase equilibriums in the CaTiO3-LaCrO3-La2/3TiO3 quasi-ternary system have been studied by means of high-resolution powder diffraction technique using X-ray and synchrotron radiation. Over 50 La(2+y−2x)/3CaxCryTi1−yO3 compounds were synthesized by solid-state reactions in air at 1350 °C using La2O3, CaCO3, Cr2O3 and TiO2. Based on the results of X-ray phase and structural analysis, the isothermal section of the CaTiO3-LaCrO3-La2/3TiO3 phase diagram at room temperature is constructed. The A-cation deficient La(2+y−2x)/3CaxCryTi1−yO3 solid solution with different perovskite-type structures (space groups Pbnm, Imma, I4/mcm and Cmmm or P2/m) is formed in the CaTiO3-LaCrO3-La2/3TiO3 quasi-ternary system in air conditions. The compounds show high stability at high temperatures at reducing as well as at oxidizing conditions. The substances with y = 0 and y = 0.2 show n-type conductivity at 900 °C at pO2 = 10−15 to 105 Pa and with y = 0.5 show conductivity minima these shift to the oxygen reach region with increasing A-site deficiency. The A-site deficient La(2+y−2x)/3CaxCryTi1−yO3 samples have higher sintering ability in comparison with the cation stoichiometric La1−xCaxCr1−yTiyO3 compositions and, in contrast to the latter, can be prepared as gas dense ceramics in air at temperatures lower as 1300 °C. Thermal expansion of the A-site deficient La(2+y−2x)/3CaxCryTi1−yO3 ceramics is comparable with that of yttrium stabilised zirconia (YSZ). No interaction between La(2+y−2x)/3CaxCryTi1−yO3 and YSZ ceramics up to 1300 °C was observed. Oxygen mobility in these ceramics can be characterised with chemical diffusion coefficients (1–9) × 10−9 cm2 s−1 at 900 °C and pO2 = 1000–21,000 Pa.