Negative thermal expansion in Y2W3O12

Neutron diffraction data were collected on polycrystalline Y2W3O12 at seven temperatures from 15 to 1373 K. All three cell edges of orthorhombic Y2W3O 12 decrease with increasing temperature, giving an average linear thermal e xpansion coefficient of -7.0 x 10(-6) K-1. Rietveld refinements of the neut ron diffraction data show an apparent decrease in the average W-O distance of 0.05 Angstrom from 15 to 1373 K. This apparent decrease causes the decre ase in the cell edges, but it is not an actual decrease of average W-O dist ances. The apparent shrinkage is instead considered to be caused by the tra nsverse thermal motion of oxygen in the Y-O-W linkages. (C) 1999 Elsevier S cience Ltd. All rights reserved.