Young's modulus was measured over the temperature range 77°-850°K by an accurate resonance technique. Data are presented for single crystals of aluminum oxide with various orientations of the crystallographic axes and for polycrystalline aluminum oxide, thorium oxide, and magnesium oxide. The results show that the range of validity of a $T^4$ temperature dependence predicted by theory must be quite small. The temperature dependence is very well described over the whole temperature range by $T\exp (-\frac{T_0}{T})$, where $T_0$ is an empirical parameter.

• Received 3 February 1961

DOI:https://doi.org/10.1103/PhysRev.122.1754