Structural investigation of the negative-thermal-expansion material ZrW2O8

• Published in: Acta crystallographica. Section B, Structural science Structural science, 1999-06, Vol.55 (3), p.333-340
• Main Authors: Evans, John S. O., David, W. I. F., Sleight, A. W.
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Heat capacities of solids; Inorganic compounds; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Thermal expansion; thermomechanical effects and density; Thermal properties of condensed matter; Thermal properties of crystalline solids
• ISSN: 0108-7681; 1600-5740
• DOI: 10.1107/S0108768198016966

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 α‐ZrW2O8 has a negative coefficient of thermal expansion, α = −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. α‐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.