Negative thermal expansion (NTE) materials possess a low-density, open structure which can respond to high pressure conditions, leading to new compounds and/or different physical properties. Here we report that one such NTE material—white, insulating, orthorhombic Sc2W3O12 transforms into a black compound when treated at 4 GPa and 1400 oC. The high pressure phase, Sc 0·67WO4, crystallizes in a defect-rich wolframite-type structure, a dense, monoclinic structure (space group P2/c) containing 1-D chains of edge-sharing WO6 octahedra. The chemical bonding of Sc0·67WO4 vis-à-vis the ambient pressure Sc2W3O12 phase can be understood on the basis of the Sc defect structure. Magnetic susceptibility, resistivity, thermoelectric power and IR spectroscopic measurements reveal that Sc0·67WO4 is a paramagnet whose conductivity is that of a metal in the presence of weak localization and electron-electron interactions. Oxygen vacancies are suggested as a potential mechanism for generating the carriers in this defective wolframite material.
Revised: September 22, 2010 |
Published: July 7, 2010
Citation
Varga T., J. Mitchell, J. Wang, L. Arnold, B.H. Toby, and C. Malliakas. 2010.High-pressure Synthesis, Crystal and Electronic Structures of a New Scandium Tungstate, Sc0·67WO4.Journal of Solid State Chemistry 183, no. 7:1567-1573.PNNL-SA-70372.doi:10.1016/j.jssc.2010.04.039