Structural, vibrational, and electronic properties of BaReH₉ under pressure

We present a study of the high-pressure behavior of BaReH₉, a novel hydrogen-rich compound, using optical, Raman, and infrared spectroscopy as well as synchrotron x-ray diffraction. The x-ray diffraction measurements demonstrate that BaReH₉ retains its hexagonal structure on room temperature compression up to 40 GPa. Optical absorption shows the absence of a gap closure to 80 GPa. Raman and IR spectra reveal the pressure evolution of a newly observed phonon peak, and large peak broadening with increasing pressure. These data constrain the disorder present in the material following the P-T paths explored.