Local structure in ZrW(2)O(8) from neutron total scattering.

The local structure of the low-temperature ordered phase of the negative thermal expansion (NTE) material ZrW(2)O(8) has been investigated by reverse Monte Carlo (RMC) modelling of neutron total scattering data. The local structure is described using the instantaneous distributions of bond lengths and angles obtained from the RMC-derived models which are simultaneously consistent with the average crystal structure. These results, together with their variation with temperature, show that the majority of the mean squared displacements of the atoms are accounted for by rigid unit mode (RUM) motions of the ZrO(6) octahedra and WO(4) tetrahedra. The detailed structural description presented in this paper further supports the dominance of the basic RUM interpretation of NTE in ZrW(2)O(8) where rigid ZrO(6) and WO(4) polyhedra are joined by flexible Zr-O-W linkages.