High-pressure study of ScH3: Raman, infrared, and visible absorption spectroscopy

Raman, IR, and visible absorption spectra of scandium trihydride (ScH₃) have been measured at high pressures up to 50 GPa, to investigate the structural and electronic phase transitions. Successive hcp-intermediate-fcc phase transitions were observed at 25 and 46 GPa by Raman and IR measurements. It was suggested that the intermediate phase of ScH₃ takes the same structure as that of YH₃ with a long periodicity of the stacking of the metal planes. The visible absorption spectra allowed us to determine that the energy gap of ScH₃ is 1.7 eV at the ambient condition and is closed around 50 GPa, at which the crystal structure transforms to fcc.