Synthesis, crystal structure, and characterization of the new ordered hollandite-type NdMo6O12

Single crystals of NdMo6O12 were prepared by fused-salt electrolysis at 960 degrees C from a melt of Rb2MoO4, MoO3, and Nd2O3 having the molar ratio 8.4:5:1. The compound crystallizes in the tetragonal space group I4/m with a = 9.8988(2) Angstrom, c = 8.6434(5) Angstrom, V= 846.93(5) Angstrom(3), and Z= 4. The structure of NdiMo(6)O(12) has been determined from single-crystal X-ray diffraction data and refined to reliability factors of R(F-o,)= 0.0409 and R-w(F-o(2)) = 0.0612 for all the reflections (1282). NdMo6O12 adopts a hollandite-related structure with a tripled c-axis, Within the double chains of edge-sharing MoO6 octahedra, the Mo atoms form infinite chains of Mo-3, triangular clusters. Another dominant feature of the structure is the ordering of the Nd3+ cations within the channels delimited by the Mo-O double strings. NdMo6O12 shows semiconducting behavior along the chains with an activation energy of 0.3 eV and a room-temperature resistivity of 0.49 Omega.cm. The magnetic susceptibility data indicate paramagnetic behavior due to the Nd3+ moment at high temperature. (C) 1998 Academic Press.