Elasticity of single-crystal MgAl2O4 spinel up to 1273 K by Brillouin spectroscopy

Abstract

The adiabatic single-crystal elastic constants, C ij , of stoichiometric magnesium aluminate spinel (MgAl2O4) have been measured up to 1273 K by highresolution Brillouin spectroscopy, using a 6-pass tandem Fabry-Perot interferometer and an argon ion laser (514.5 nm). Two platelet samples were employed for probing the acoustic phonons along [100] and [110] directions by platelet and backscattering geometries. The measured temperature dependences of the elastic moduli show a distinct anomaly at 923 K in the shear modulus C s = (C11-C12)/2 (along [110] direction) and the longitudinal modulus C11 (along [100] direction). This anomaly is consistent with the order-disorder phase transition, resulting from the atomic exchange between Mg at the tetrahedral site and Al at the octahedral site, which has been well documented recently (Peterson et al. 1991; Millard et al. 1992) by neutron powder diffraction and 27Al magic-angle spinning NMR. The values of the temperature derivatives of v p , v s , and K s , in the temperature range 300–923 K, calculated by the Voigt-Reuss-Hill approximation are -0.40ms−1 K−1, -0.26ms−1 K−1, and -1.89 x 10−2GPaK−1.