Specific Heat of α Al2O3 from 2 to 25 K

The heat capacity of colorless synthetic sapphire (α Al2O3, corundum) has been measured from 2 to 25 K. The data above 14 K can be expressed as Cv = 1.755×10−3T3+1.905×10−7T5 mJ/K·g-atom. This equation for Cv gives Θ0 = 1035 K, in good agreement with the values calculated from elastic constant data. An extrapolation of these results to higher temperatures is consistent with other data. Below 14 K an anomalous heat-capacity contribution appears which is about 1.5% of Cv at its maximum. The magnitude of this anomaly corresponds to that which would be given by a few ppm of gaseous or transition-metal impurities.