NEUTRON AND X-RAY-POWDER DIFFRACTION STUDIES OF LANTHANUM MANGANITE, A NONSTOICHIOMETRIC PEROVSKITE

The defect structure of a hexagonal perovskite-type lanthanum manganite was studied using Rietveld refinement of powder diffraction data. The nominal composition of the sample was La0.85Mn1.00O3+/-delta. The structure was refined using simultaneous refinement of two sets of neutron diffraction data and one set of X-ray diffraction data in order to combine the advantages of using different types of radiation and different wavelengths. A precise determination of the occupancies of La and Mn is difficult owing to a very strong correlation between occupancies and temperature factors. These difficulties are discussed based on a series of models using various constraints on the temperature factors. It is concluded that the manganese and oxygen sublattice in the lanthanum manganite is fully occupied, whereas vacancies are present in the lanthanum sublattice.