Raman Evidence for Pressure-Induced Phase Transition in Barium Carbonate

Raman scattering experiments were performed on barium carbonate at ambient temperature and high pressure within a hydrostatic environment, employing liquid nitrogen as the pressure-transmitting medium. This approach allowed for the investigation of hydrostatic pressure effects on the barium carbonate structure. Previous studies suggest that the stability threshold of the orthorhombic barium carbonate structure lies around 8 GPa. At pressures ranging from 8 to 10 GPa, the material exhibited a mixed phase. Upon reaching 10 GPa, the orthorhombic structure of barium carbonate vanished, giving way to a transformation into the trigonal phase. The phase transition significantly impacted the intensity of the Raman spectra, in-dicating an influence on the electronic structure, notably causing the electron cloud to rearrange and the bond character to alter. The re-emergence of the orthorhombic phase at a reduced pressure of 5.3 GPa und-erscored the pronounced hysteresis phenomena associated with the phase transition of barium carbonate. We determined that, while this phase transition is reversible upon pressure release, it is accompanied by persistent characteristic peaks of the trigonal phase, suggesting incomplete transformation back to the orthorhombic phase during decompression, with the residual proportion of the trigonal phase constituting approximately 12%.