HIGH-PRESSURE RAMAN AND X-RAY DIFFRACTION STUDY OF PHASE TRANSITIONS IN PbSiO3 POLYMORPHS

The objective of this study is to determine the phase transformations of the PbSiO3 (PS) polymorphs, as a function of hydrostatic pressure. Using in situ high-pressure Raman spectroscopy and synchrotron X-ray diffraction, we analyze the structural evolution of three PS polymorphs corresponding to successive stages of its temperature-driven crystallization from a melt precursor: the monoclinic alamosite, the hexagonal, and a metastable low-symmetry phase. Pressure-induced transitions occur in the monoclinic and hexagonal polymorphs at ∼5 GPa, whereas the low-symmetry phase shows the onset of structural disorder near 8 GPa. All polymorphs destabilize above 18 GPa. The determination of the third-order Birch–Murnaghan isothermal equation of state yielded bulk moduli and first derivatives of B 0 = 52 GPa, B 0 ′ = 10 for alamosite, and B 0 = 48 GPa, B 0 ′ = 6 for the hexagonal phase. These results provide fundamental insights into the compression mechanisms of the lead-silicate phases and yield essential parameters for thermodynamic modeling. From an applied perspective, we demonstrate that moderate pressures, accessible with large-volume presses, can effectively modulate the crystallization pathway by inducing phase transitions that alter the relative energy of the crystallization stages — an approach that may extend to other silicate systems.