Estimation of single-crystal elastic moduli from polycrystalline X-ray diffraction at high pressure: Application to FeO and iron

X-ray diffraction data obtained under nonhydrostatic compression of a polycrystalline sample yield an estimate of the single-crystal elasticity tensor of the material when analyzed using appropriate equations. The analysis requires as input the aggregate shear modulus from independent measurements. The high-pressure elastic moduli of face-centered-cubic FeO, body-centered-cubic iron (alpha-Fe), and the pressure-induced hexagonal close-packed iron (epsilon-Fe) are obtained. This analysis currently provides the only method of determining single-crystal elasticity tensors in the megabar pressure range and of studying elasticity of very high-pressure phases.