The ZrW 2 O 8 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 ZrW 2-x Mo x O 8 phases. ZrWMoO 8 shows significant negative thermal expansion (R l ) -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 R and β forms of the material with ∆V disorder ) -0.24%. A negative volume change for an order-disorder transition is unusual.

2001 mechanical properties, thermal properties mechanical properties, thermal properties D 3000 -014Low-Temperature Oxygen Migration and Negative Thermal Expansion in ZrW 2−x MoxO 8 .-Variable-temperature powder neutron diffraction measurements reveal a negative thermal expansion coefficient of -8.7·10 −6 K −1 for ZrWMoO 8 and oxygen migration at temperatures as low as 200 K with an activation energy of 0.23 eV. The compound undergoes a phase transition from the disordered β form to the ordered α form at around 270 K. -(EVANS, J. S. O.; HANSON, P. A.; IBBERSON, R. M.; DUAN, N.; KAMESWARI, U.; SLEIGHT, A. W.; J. Am. Chem. Soc. 122 (2000) 36, 8694-8699; Dep. Chem., Univ. Durham, Durham DH1 3LE, UK; EN)