Electronic State of Bismuth in BaBiO₃ up to 9 GPa Investigated by Optical Spectroscopy

Effects of hydrostatic pressure on the mixed-valence (MV) bismuth complex BaBiO₃ have been investigated up to ～9 GPa by means of high-pressure Raman scattering and absorption spectra at 300 K. The pressure-induced hardening behaviour of the Bi-O stretching mode suggests that the predicted pressure-induced MV to the single-valence (SV) phase change cannot occur. Investigation of absorption spectra with pressure shows the enhanced optical gap E_gap, which further indicates the remained MV state of Bi ions.