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

Deficiency in the A sublattice of orthorhombic perovskite-type La1−xNi0.5Ti0.5O3−δ, with maximum at x=0.07–0.08x=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−δ ceramics, calculated from dilatometric data in air, increases from 8.6×10−6K−1 at 300–800 K to 12.0×10−6K−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 9.5×10−59.5×10−5–8.1×10−48.1×10−4 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)p(O2) range 9×10−119×10−11 to 8×10−9atm at 1073–1223 K. The low-p(O2)p(O2) stability limit of La0.95Ni0.5Ti0.5O3−δ perovskite was found between that of La3Ni2O7 and Ni/NiO boundary.

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