Mixed conductivity, thermal expansion and defect chemistry of A-site deficient LaNi0.5Ti0.5O3−δ

This work is focused on the analysis of defect chemistry and partial electronic and oxygen ionic conductivities of A-site deficient La1−xNi0.5Ti0.5O3−δ (x = 0.05 and 0.10). The orthorhombic-to-rhombohedral phase transition was monitored by means of dilatometry and high-temperature X-ray diffractometry. The average thermal expansion coefficients vary in the range (8.5–13.0) × 10−6 K−1, increasing with temperature and A-site deficiency. The ion transference numbers determined by the Faradaic efficiency measurements are lower than 0.1% at 900–975 °C in air. Activation energies of the oxygen ionic conductivity at 897–977 °C are 430 and 220 kJ/mol for x = 0.05 and 0.10, respectively. Atomistic simulation demonstrated high stability of ternary defect clusters formed by the vacant sites in the A-sublattice, oxygen vacancies and Ni3+ cations, which leads to a very low level of mixed conductivity.