P-V-T equation of state of alpha-ScOOH

In this study, an in situ X-ray diffraction study of alpha-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 secondorder Birch-Murnaghan EoS to the P-V-T data, the EoS parameters of alpha-ScOOH were determined as bulk modulus K-To = 101(1) GPa, (partial derivative K-T/partial derivative T)(P) = -0.009(5) GPa K-1, and thermal expansion coefficient at zero pressure alpha = 3.12(6) 10(-5) K-1. alpha-ScOOH exhibits anisotropic compression and thermal expansion behaviors, which are consistent with those of previous studies on diaspore-type oxyhydroxides. alpha-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).