Defect formation and transport in La0.95Ni0.5Ti0.5O3-δ

Deficiency in the A sublattice of orthorhombic perovskite-type La1-xNi0.5Ti0.5O3-delta, 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 Ni3+ cations and low electronic and oxygen-ionic transport. The average thermal expansion coefficient of La0.95M0.5Ti0.5O3-delta ceramics, calculated from dilatometric data in air, increases from 8.6 x 10(-6) K-1 at 300-800 K to 12.0 x 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 U/mol, respectively. The oxygen ion transference numbers determined by the faradaic efficiency measurements in air, vary in the range 9.5 x 10(-5)-8.1 x 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 x 10(-11) to 8 x 10(-9) atm at 1073-1223 K. The low-p(O-2) stability limit of La0.95M0.5Ti0.5O3-delta perovskite was found between that of La3Ni2O7 and Ni/NiO boundary. (c) 2006 Elsevier Masson SAS. All rights reserved.