Specific Heat of α Al2O3 from 2 to 25 K

Abstract

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 C_v = 1.755×10⁻³T³+1.905×10⁻⁷T⁵ mJ/K·g‐atom. This equation for C_v 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 C_v 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.