Equation of state ofMgAl2O4spinel to 65 GPa

Abstract

Compression measurements on synthetic ${\mathrm{MgAl}}_2{\mathrm{O}}_4$ spinel, obtained by quasihydrostatic x-ray powder diffraction at room temperature, are in good agreement with ultrasonically determined values of the bulk modulus and its pressure derivative at zero pressure. Contrary to previous extrapolations of the ultrasonic data, from which an elastic (volume) instability had been predicted at $\sim 25\mathrm{GPa},$ our results show that the spinel structure is (meta)stable from 0 to 65 GPa. The zero-pressure values of the bulk modulus and its pressure derivatives which best fit all the available data are $K_0=196(\pm 1)\mathrm{GPa},$ $K_0^{\prime }=4.7(\pm 0.3),$ and $K_0{K}_0^{″}\approx -6.$