Crystal structure of lithium molybdenum purple bronze Li 0.9Mo 6O 17

Abstract

The crystal structure of the molybdenum ternary oxide Li 0.9Mo 6O 17 is determined by single-crystal X-ray diffraction. The crystal is monoclinic with space group P2 1 m and the lattice constants are a = 12.762(2) Å, b = 5.523(1) Å, c = 9.499(1) Å, β = 90.61(1)°, Z = 2. Full-matrix least-squares refinement gives the final values of R( F) = 0.033 and R w ( F) = 0.066 for 3019 independent reflections. The unit cell contains six crystallographically independent molybdenum sites. One-third of the molybdenum atoms are located in oxygen tetrahedra, while the others are within oxygen octahedra. The structure is built up of slabs of the MoO 6 octahedra. Each slab consists of three layers of distorted ReO 3-type MoO 6 octahedra sharing corners. The structure is rather different from that of K 0.9Mo 6O 17, although the layered feature is still preserved. The lithium ions are located in the large vacant sites between the slabs. By the application of Zachariasen's bond length-bond strength relation to the observed MoO bonds, most of the conduction electrons are found to be located in the Mo(1) and Mo(4) octahedral sites which are associated in pairs to form the Mo(1)O(11)Mo(4)O(11) double zigzag chains extending along the b-axis. Therefore the structural properties are considered to lead to the highly anisotropic electronic transport.