Phase transitions of ScOOH under high pressure

In-situ X-ray diffraction measurements of ScOOH were conducted under high pressure and temperature conditions up to 11 GPa and 900 K to understand its phase transitions. As the pressure increased, α-ScOOH, InOOH-type ScOOH, and YbOOH-type ScOOH were observed. The experimental results indicate that the boundaries between α-ScOOH and InOOH-type ScOOH, and between InOOH-type and YbOOH-type ScOOH are represented by the following linear equations: P(GPa) = (0.0009 ± 0.0015) × [T(K) – 700] + 4.33 ± 0.04 and P(GPa) = (–0.0029 ± 0.0002) × [T(K) – 800] + 8.1 ± 0.3, respectively. By using a least-squares fit of the second-order Birch–Murnaghan equation of state (EoS) to the experimental compression data, the EoS parameters of the three phases of ScOOH at 400 K were obtained. The volume change of the transition from α-ScOOH to InOOH-type ScOOH is ∼3.9% at 4 GPa and 400 K, while the volume change of the transition from InOOH-type to YbOOH-type ScOOH is ∼7.6% at 9 GPa and 400 K.