YMoO4 revisited: the crystal structure of Y5Mo4O18

Abstract

Analytical electron microscopy and X-ray powder diffraction have been used to show that the ‘compound’ YMoO₄ is a mixture of two oxides having the approximate compositions Y₅Mo₄O₁₈ and Y₂Mo₃O₁₀. Furthermore, the phase previously described as a high-temperature form of YMoO₄ is shown to be a silicate, the silicon being leached out of the silica tubes used as reaction vessels during the synthesis of the compound. The crystal structure of the yttrium-rich phase has been refined from neutron powder diffraction data: space group I4₁/a, a= 5.176 67(2)Å, c= 11.004 51(7)Å. The structure is that of a defect scheelite with extensive disorder on both the molybdenum and oxygen sublattices. The stoichiometry refined to the formula Y₅Mo_3.85O_17.3.