resumo
A statistical thermodynamic approach to analyze defect thermodynamics in strongly nonideal solid solutions was proposed and validated by a case study focused on the oxygen intercalation processes in mixed-conducting LaGa0.65Mg0.15Ni0.20O3-delta perovskite. The oxygen nonstoichiometry of Ni-doped lanthanum gallate, measured by coulometric titration and thermogravimetric analysis at 923-1223 K in the oxygen partial pressure range 5x10(-5) to 0.9 atm, indicates the coexistence of Ni2+, Ni3+, and Ni4+ oxidation states. The formation of tetravalent nickel was also confirmed by the magnetic susceptibility data at 77-600 K, and by the analysis of p-type electronic conductivity and Seebeck coefficient as function of the oxygen pressure at 1023-1223 K. The oxygen thermodynamics and the partial ionic and hole conductivities are strongly affected by the point-defect interactions, primarily the Coulombic repulsion between oxygen vacancies and/or electron holes and the vacancy association with Mg2+ cations. These factors can be analyzed by introducing the defect interaction energy in the concentration-dependent part of defect chemical potentials expressed by the discrete Fermi-Dirac distribution, and taking into account the probabilities of local configurations calculated via binomial distributions.
palavras-chave
PEROVSKITE-RELATED OXIDES; IONIC-CONDUCTIVITY; LANTHANUM GALLATE; DOPED LAGAO3; ELECTRICAL-PROPERTIES; PARTIAL OXIDATION; OXYGEN NONSTOICHIOMETRY; CERAMIC MEMBRANES; TRANSPORT; FE
categoria
Physics
autores
Naumovich, EN; Kharton, VV; Yaremchenko, AA; Patrakeev, MV; Kellerman, DG; Logvinovich, DI; Kozhevnikov, VL
nossos autores
Aleksey Yaremchenko
Investigador Principal