An investigation of the Nd2O3-MoO3 phase system : thermal decomposition of Nd2Mo4O15 and formation of Nd6Mo10O39.

Abstract

A new neodymium molybdate, Nd6Mo10O39, has been identified in the Nd2O3–MoO3 phase system. Nd6Mo10O39 appears to be a metastable phase, which does not form directly from a stoichiometric mixture of Nd2O3 and MoO3 oxides. Instead, it can be obtained by thermal decomposition of Nd2Mo4O15. Nd2Mo4O15 usually decomposes into Nd2(MoO4)3, and the formation of Nd6Mo10O39 critically depends on the heating regime used. The structure of Nd6Mo10O39 has been determined by single crystal X-ray diffraction. It crystallizes in the monoclinic space group C2/c, with unit cell parameters of , , , β=100.767(2)°, at 120 K. Nd atoms are seven and eight coordinate, and pairs of coordination polyhedra share edges and faces, respectively, to form Nd2O12 and Nd2O13 groups. All Mo atoms are in tetrahedral coordination environments, with some of the tetrahedra sharing corners to form pyromolybdate groups.