Defect formation and transport in La 0.95Ni 0.5Ti 0.5O 3− δ

Abstract

Deficiency in the A sublattice of orthorhombic perovskite-type La 1− x Ni 0.5Ti 0.5O 3− δ , with maximum at x = 0.07 – 0.08 , is compensated by the formation of trivalent nickel and oxygen vacancies. The atomistic computer simulations showed that these defects are trapped near the A-site cation vacancies, resulting in the stabilization of Ni 3+ cations and low electronic and oxygen-ionic transport. The average thermal expansion coefficient of La 0.95Ni 0.5Ti 0.5O 3− δ ceramics, calculated from dilatometric data in air, increases from 8.6 × 10 −6 K −1 at 300–800 K to 12.0 × 10 −6 K −1 at 1300–1500 K. The data on Seebeck coefficient and total conductivity, predominantly p-type electronic, suggest a broadband mechanism of hole transport. The activation energies for the hole and ionic conductivities are 89 and 430 kJ/mol, respectively. The oxygen ion transference numbers determined by the faradaic efficiency measurements in air, vary in the range 9.5 × 10 −5 – 8.1 × 10 −4 at 1173–1248 K, increasing with temperature. Reducing oxygen partial pressure leads to a moderate decrease of the conductivity, followed by phase decomposition in the p ( O 2 ) range 9 × 10 −11 to 8 × 10 −9 atm at 1073–1223 K. The low- p ( O 2 ) stability limit of La 0.95Ni 0.5Ti 0.5O 3− δ perovskite was found between that of La 3Ni 2O 7 and Ni/NiO boundary.