Pressure-induced phase transition of lead phosphate Pb 3 (PO 4 ) 2 : X-ray diffraction and XANES.

Lead phosphate Pb3(PO4)2was investigated byin situsynchrotron 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 Pb3(PO4)2was observed from monoclinic (C2/c) to trigonal () phases at about 1.7 GPa at room temperature. The high-pressure annealing experiment indicates that the trigonal phase of Pb3(PO4)2is stable at least up to 60.9 GPa. Isothermal pressure–volume relationship of trigonal Pb3(PO4)2is well described by the third-order Birch–Murnaghan equation of state withV0= 533(1) Å3,K0= 89(4) GPa andK0′= 5.8(2). In trigonal Pb3(PO4)2, thea-axis is more compressible than thec-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 ofC2/c-to-phase transition. [ABSTRACT FROM AUTHOR]