Crystal structure of Fe-doped lanthanum gallate for oxygen partial pressures studied by neutron powder diffraction

Neutron powder diffraction experiments were carried out to investigate a change in a crystal structure of La(0.8)Sr(0.2)Ga(0.65)Fe(0.35)O(3) for oxygen partial pressures, P(O2), at 800 degrees C. The crystal structure was refined on the basis of the R3c syrnmetry for the P(O2) range from 10(-1) to 10(-20) atm, by the Rietveld analysis. It was found that lattice parameters, a and c, monotonically expand with decreasing P(O2), and then both expansions are rapidly suppressed below 10(-4) atm. In the meantime, I(M-O) and I(O-O)(2) also discontinuously increased with decreasing P(O2), while I(O-O)(1) did not change at all P(O2), where I(M-O), I(O-O)(1) and I(O-O)(2) are the bond lengths within a MO(6) octahedron (M = Ga(0.65)Fe(0.35)). This result indicates that the I(M-O) and the I(O-O)(2) are more important than the I(O-O)(1) for such a complicated lattice expansion for P(O2). (C) 2008 Elsevier B.V. All rights reserved.