High-pressure synchrotron x-ray diffraction and Raman spectroscopic study of plumbogummite

PbAl3(PO4)(2)(OH, H2O)(6), an important environmental mineral, is in-situ studied by synchrotron x-ray diffraction (XRD) and Raman scattering combined with diamond anvil cells (DACs) at pressures up to similar to 11.0 GPa and room temperature. The XRD results indicate that plumbogummite does not undergo a phase transition between 0 GPa and 10.9 GPa. Moreover, the c axis is more compressible than the a axis, revealing its anisotropic behavior. The pressure-volume data are fitted to the third-order Birch-Murnaghan equation of state to yield the plumbogummite bulk modulus K-0 of 68(1) GPa and K'0 of 6.1. The [PO4](3-) and [HPO4](2-) Raman vibrational modes exhibit scale nearly linearly as a function of pressure. The [PO4](3-) stretching modes are generally more sensitive to pressure than the bending modes. The Gruneisen parameters range from -0.07 to 1.19, with an arithmetic mean of approximately 0.39.