P-V-T equation of state of α-ScOOH.

ABSTRACT In this study, an in situ X-ray diffraction study of α-ScOOH, scandium oxyhydroxide with a diaspore-type structure, was conducted at a pressure and temperature of up to 4.12 GPa and 700 K, respectively, to determine the pressure-volume-temperature (P-V-T) equation of state (EoS). Using a least-squares fit of the second-order Birch–Murnaghan EoS to the P-V-T data, the EoS parameters of α-ScOOH were determined as bulk modulus KT 0 = 101(1) GPa, (∂KT /∂T) P  = −0.009(5) GPa K−1, and thermal expansion coefficient at zero pressure α = 3.12(6) 10−5 K−1. α-ScOOH exhibits anisotropic compression and thermal expansion behaviors, which are consistent with those of previous studies on diaspore-type oxyhydroxides. α-ScOOH is more compressible than other diaspore-type oxyhydroxides, and the product of the bulk modulus and volume is approximately constant among diaspore-type M3 + OOH (M = Al, Sc, and Fe).