Raman Investigation of BaWO4-II Phase under Hydrostatic Pressures up to 14.8GPa

The BaWO4-II phase is synthesized at 5.0GPa and 610°C with a cubic-anvil apparatus and identified by XRD. Raman scattering measurement is carried out to investigate the phase behaviour of a pure BaWO4-II phase (space group P21/n, Z=8) under hydrostatic pressures up to 14.8GPa at ambient temperature. In each spectrum recorded for this phase, 27 Raman modes are observed, and all bands shift toward higher wavenumber with a pressure dependence ranging from 3.8 to 0.2cm-1/GPa. No pressure-driven phase transition occurs in the entire pressure range in this study. Our results indicate that the previously reported high pressure phase of BaWO4 at pressure above about 10GPa and room temperature (Errandonea et al. Phys. Rev. B 73(2006)224103) is not the BaWO4-II phase.