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Low-Temperature Oxygen Migration and Negative Thermal Expansion in ZrW2-xMoxO8

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journal contribution
posted on 26.08.2000, 00:00 by J. S. O. Evans, P. A. Hanson, R. M. Ibberson, N. Duan, U. Kameswari, A. W. Sleight
The ZrW2O8 family of materials has been shown to display the unusual property of an isotropic bulk contraction in volume as a function of temperature. We report here on negative thermal expansion properties and oxygen migration at very low temperatures in ZrW2-xMoxO8 phases. ZrWMoO8 shows significant negative thermal expansion (αl = −8.7 × 10-6 K-1) and oxygen migration at temperatures as low as 200 K with an activation energy of 0.23 eV. We are unaware of oxygen migration at such low temperatures in other electronic insulators. The low-temperature migration is associated with an order−disorder transition between the α and β forms of the material with ΔVdisorder = −0.24%. A negative volume change for an order−disorder transition is unusual.