Abstract
The Voigt‐Reuss‐Hill (VRH) approximation, a useful scheme by which one calculates isotropic polycrystalline elastic moduli in terms of the anisotropic single‐crystal elastic constants, is shown to be accurately applicable for ZnO, TiO2 (rutile), and α‐Al2O3, which are the simplest examples of oxide materials with the hexagonal, tetragonal, and trigonal symmetries, respectively. An experimental proof is established by measuring isotropic elastic moduli on dense‐formed polycrystalline specimens. The recommended values of the polycrystalline isotropic elastic moduli of these oxides at room temperature are as follows: for ZnO, G=4.56(±0.04) and E=12.35(±0.09); for TiO2, G=11.15(±0.09) and E=28.42(±0.14); and for α‐Al2O3, G=16.35(±0.12) and E=40.39(±0.31), where G and E are the isotropic shear and Young's moduli, respectively, and they are in units of 1011 dyn/cm2.