The high-temperature cell parameters of lime (CaO), periclase (MgO), corundum (Al₂O₃), and spinel (MgAl₂O₄) have been determined from 300 up to 3000 K through X-ray diffraction experiments with synchrotron radiation. The good agreement found with dilatometric results suggests that vacancy-type defects do not make a large contribution to thermal expansion for these oxides, even near the melting point, justifying the use of X-ray diffraction for determining volume properties up to very high temperatures. Thermal expansion coefficients were determined from the measured cell volumes with equations of the formα=α₀ + α₁T + α₂/T ². Along with available isobaric heat capacity and compressibility data, these derived coefficients clearly show that anharmonic effects contribute little to the isochoric heat capacities (C_v) of CaO, MgO, and Al₂O₃, which do not depart appreciably from the 3nR Dulong and Petit limit.

Authors and Affiliations

1. Laboratoire des Sciences de la Terre, UMR CNRS 5570 Ecole Normale Supérieure de Lyon, 69364 Lyon cedex 07, France, , , , , , FR

   G. Fiquet

2. Institut de Physique du Globe, ESA CNRS 7046 4 place Jussieu, 75252 Paris cedex 05, France, , , , , , FR

   P. Richet

3. Laboratoire des Sciences de la Terre, UMR CNRS 5570 Ecole Normale Supérieure de Lyon, 69364 Lyon cedex 07, France, , , , , , FR

   G. Montagnac

Received: 31 March 1999 / Revised, accepted: 23 June 1999

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