Pressure-induced phase transition of lead phosphate Pb-3(PO4)(2): X-ray diffraction and XANES

Lead phosphate Pb-3(PO4)(2) was investigated by in situ synchrotron radiation X-ray diffraction and X-ray absorption near-edge structure (XANES) combined with diamond anvil cell technique up to 60.9 GPa. A pressure-induced phase transition of Pb-3(PO4)(2) was observed from monoclinic (C2/c) to trigonal ( [GRAPHICS] ) phases at about 1.7 GPa at room temperature. The high-pressure annealing experiment indicates that the trigonal phase of Pb-3(PO4)(2) is stable at least up to 60.9 GPa. Isothermal pressure-volume relationship of trigonal Pb-3(PO4)(2) is well described by the third-order Birch-Murnaghan equation of state with V-0 = 533(1) angstrom(3), K-0 = 89(4) GPa and K-0(') = 5.8(2). In trigonal Pb-3(PO4)(2), the a-axis is more compressible than the c-axis, showing an anisotropy elasticity. XANES results reveal the evolution of Pb local environment, i.e. the first-shell coordination number of Pb1 changes from 9 to 12 and the average Pb-O bond length increases at the crossover of C2/c-to- [GRAPHICS] phase transition.