In-situ X-ray diffraction study on β-CrOOH at high pressure and high-temperature

High pressure hydrous phases with distorted rutile-type structure have attracted much interest as potential water reservoirs in the Earth's mantle. An in-situ X-ray diffraction study of beta-CrOOH was performed at high pressures of up to 6.2 GPa and high-temperatures of up to 700 K in order to clarify the temperature effect on compression behaviors of beta-CrOOH. The P-V-T data fitted to a Birch-Murnaghan equation of state yielded the following results: isothermal bulk modulus K-T0 = 191(4) GPa, temperature derivative ( partial differential K-T/ partial differential T)(P) = -0.04(2) GPa K-1, and volumetric thermal expansion coefficient alpha = 3.3(2) x 10(-5) K-1. In this study, at 300 K, the a-axis became less compressible at pressures above 1-2 GPa. We found that the pressure where the slopes of a/b and a/c ratios turned positive increased with temperature. This is the first experimental study indicating the temperature dependence of the change in the axial compressibility in distorted rutile-type M3+OOH.