High-pressure Raman study on the series

High-pressure Raman spectroscopic studies of the BaSO4–SrSO4 binary series are carried out. The variations of the Raman spectra show 1–2 bonding-state transitions. The first pressure transition may be in relation to the re-arrangement of Ba–O/Sr–O or S–O, while the second one may indicate an indistinct structural transition leading to some structural degeneracies. It is observed that the transition occurs at a lower pressure with increasing BaSO4 molar ratio. Moreover, the radius of the cations is the main factor in the transformations of the sulfates with pressures. Barite (BaSO4), celestine (SrSO4), and their solid solutions have the same transitional behavior, and their transitions with pressures are all regarded as reversible.