Thermal expansion at elevated temperatures. II. Aluminium oxide: experimental data between 100 and 800 K and their analysis

Using applications of interferometric apparatus described previously, earlier uncertainties in the linear coefficients of thermal expansion of high purity single crystal alpha -Al2O3 have been resolved in the a and c crystallographic axis directions between approximately 100 and 800 K. The results have been used in association with related measurements of specific heat, elastic constants and their pressure dependence to calculate the mean Gruneisen parameter as a function of temperature, the temperature dependences of a weighted average of the vibrational frequencies and of the geometric mean frequency of the spectrum. Values of the moments nu n of the frequency distribution f( nu ) have been calculated for -3<or=n<or=6, and their dimensional dependences gamma /sub ///(n) and gamma perpendicular to (n), corresponding to directions parallel and perpendicular to the c crystallographic axis direction respectively, have been derived for -3<or=n<or=4. Finally, the signs of the first and second anharmonic coefficients in the specific heat and entropy have been identified, together with that of the anharmonic contribution to the Gruneisen parameter, and the magnitude of the first of these quantities has been assessed at (0<A<2)*10-5K-1.