Negative Thermal Expansion from 0.3 to 1050 Kelvin in ZrW ₂ O ₈

Negative thermal expansion was found for ZrW 2 O 8 from 0.3 kelvin to its decomposition temperature of about 1050 kelvin. Both neutron and x-ray diffraction data were used to solve and refine the structure of this compound at various temperatures. Cubic symmetry persists for ZrW 2 O 8 over its entire stability range. Thus, the negative thermal expansion behavior is isotropic. Essentially the same behavior was found for isostructural HfW 2 O 8 . No other materials are known to exhibit such behavior over such a broad temperature range. These materials are finding applications as components in composites in order to reduce the composites' overall thermal expansion to near zero.