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

Yakovlev, S., Kharton, V., Naumovich, E., Zekonyte, Jurgita, Zaporojtchenko, V., Kovalevsky, A., Yaremchenko, A. and Frade, J. (2006) Defect formation and transport in La0.95Ni0.5Ti0.5O3?? Solid State Sciences, 8 (11), 1302-1311. (doi:10.1016/j.solidstatesciences.2006.07.010).

Abstract

Deficiency in the A sublattice of orthorhombic perovskite-type La1?xNi0.5Ti0.5O3??, 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 La0.95Ni0.5Ti0.5O3?? ceramics, calculated from dilatometric data in air, increases from at 300–800 K to 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(O2) range 9×10?11 to at 1073–1223 K. The low-p(O2) stability limit of La0.95Ni0.5Ti0.5O3?? perovskite was found between that of La3Ni2O7 and Ni/NiO boundary.

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