The results of O non-stoichiometry, linear expansion and electrical conductivity measurements were presented for selected (La,Sr)(Cr,V)O3 and (La,Ca)(Cr,Al,Co)O3 compositions at 1000C. The modelling of the defect structure of the O deficient chromites was carried out by considering both donor (V) and acceptor (Co) dopant on the B-site. The equilibrium constants, required to calculate all a priori unknown equilibrium defect concentrations, were determined by fitting the derived model equation to the measured O non-stoichiometry data for both cases. The two oxidation states, 4+ and 3+ for V were considered simultaneously in V-doped lanthanum chromite in addition to 3+ and 4+ states for Cr in the host lattice. The Co reduction to the divalent state was apparently caused by the redox reaction, Co3++Cr3+=Co2++Cr4+, in Co-doped lanthanum chromite at high O partial pressure. The proposed defect structure was confirmed by the measurement of the electrical conductivity as a function of O partial pressure. Relative change of the average radius of the B-site ions as a function of pO2 was proposed as a criterion to reflect the influence of the defect structure alteration on the linear expansion. The criterion was in agreement with the measured isothermal expansion for the (La,Sr)(Cr,V)O3 and (La,Ca)(Cr,Al,Co)O3 systems.
Defect Structure and Isothermal Expansion of A-Site and B-Site Substituted Lanthanum Chromites. A.Zuev, L.Singheiser, K.Hilpert: Solid State Ionics, 2002, 147[1-2], 1-11