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 La0.8Sr0.2Ga0.65Fe0.35O3 for oxygen partial pressures, PO2, at 800 °C. The crystal structure was refined on the basis of the R3̄c symmetry for the PO2 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 PO2, and then both expansions are rapidly suppressed below 10− 4 atm. In the meantime, lM–O and lO–O(2) also discontinuously increased with decreasing PO2, while lO–O(1) did not change at all PO2, where lM–O, lO–O(1) and lO–O(2) are the bond lengths within a MO6 octahedron (M = Ga0.65Fe0.35). This result indicates that the lM–O and the lO–O(2) are more important than the lO–O(1) for such a complicated lattice expansion for PO2.