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

Abstract

ABSTRACTHigh 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 β-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 β-CrOOH. The P-V-T data fitted to a Birch–Murnaghan equation of state yielded the following results: isothermal bulk modulus KT0 = 191(4) GPa, temperature derivative (∂KT/∂T)P = −0.04(2) GPa K−1, and volumetric thermal expansion coefficient α = 3.3(2) × 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.