Acta Cryst. (1999). B55, 333-340 [doi:10.1107/S0108768198016966]
Abstract: High-resolution powder diffraction data have been recorded on cubic ZrW2O8 [a = 9.18000 (3) Å at 2 K] at 260 temperatures from 2 to 520 K in 2 K steps. These data have confirmed that ![[alpha]](/logos/entities/alpha_rmgif.gif)
-ZrW2O8 has a negative coefficient of thermal expansion, = -9.07 × 10-6 K-1 (2-350 K). A `parametric' approach to Rietveld refinement is adopted and it is demonstrated that a full anisotropic refinement can be performed at each temperature, despite using a data collection time of only 5 min. Examination of the resulting structural parameters suggests that the origin of the contraction with increasing temperature can be traced straightforwardly to the rigid-body transverse librations of bridging O atoms. -ZrW2O8 undergoes a phase transition from P213 to Pa3 at 448 K that is associated with the onset of considerable oxygen mobility. The phase transition can be described in terms of a simple cubic three-dimensional Ising model. Unusual kinetics are associated with this phase transition. Hysteresis in the cell parameter through the phase transition is the opposite of that normally observed.
Online 1 June 1999
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