Negative thermal expansion (NTE) materials have captured the curiosity of scientists and engineers. Active research areas include the synthesis and characterization of new materials, with the goal of tuning their properties, preparation of controlled thermal expansion composites, and experiments trying to elucidate the underlying mechanisms of this unusual behavior.Much of the work on NTE materials relies heavily on powder X-ray diffraction to confirm phase identity and purity. This is in some cases dictated by the fact that not all NTE materials are thermodynamically stable, and the need for preserving small particle sizes to ensure good mixing in composites. In addition, characterization of temperature- and pressure-dependent behavior is usually carried out on powders.NTE materials in the scandium tungstate family (A2M3O12, where A = trivalent metal, M = Mo, W) are synthesized via solution-based routes in our group. Our current focus is on compounds in which the A-site is occupied by a mixture of two cations, as this can significantly alter the magnitude of expansion coefficients and the occurrence of phase transitions. While the thermal expansion behavior can be evaluated by laboratory powder diffraction in combination with Rietveld analysis, sample homogeneity for mixed cation systems and structural differences of cation substituted compositions are best address by high resolution synchrotron or neutron diffraction. The study of high pressure phase transitions is also accomplished by synchrotron diffraction.

Powder crystallography applied to negative thermal expansion materials

247th National Meeting (2014)

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