Ab Initio Structure Determination of La34Mo8O75 Using Powder X-ray and Neutron Diffraction Data

We report the synthesis, the structure determination, and the structure analysis of La34Mo8O75, which comprises 68 mol % La2O3 in the binary system La2O3-MoO3, in place of the previously reported compound La4MoO9, 66.7 mol % La2O3. This latter compound, which was reported in the literature without any structural information, is presented in this Article as part of the exploration of the La2O3-Nb2O5-MoO3 ternary phase diagram. Several diffraction techniques were used for the structural resolution of this compound such as powder X-ray and neutron diffraction as well as transmission electron microscopy in diffraction mode. La34Mo8O75 crystallizes in the monoclinic space group C2/m with the cell parameters: a = 17.070 angstrom, b = 12.204 angstrom, c = 9.742 angstrom, beta = 109.58 degrees. The structure, related to fluorite, can be described as an anion-deficient fluorite with the global formula La34Mo8O75 square(9). The oxygen conduction of the compound was also investigated by means of complex impedance spectroscopy.