The compressibility of a natural apatite

In-situ synchrotron X-ray diffraction (XRD) experiments of a natural apatite with the formula of Ca-5(PO4)(3)F0.94Cl0.06 were carried out using a diamond anvil cell and angle-dispersive technique at Photon Factory (PF), Japan. Pressure-volume data were collected up to 7.12 GPa at 300 K. The pressures were determined from the ruby fluorescence spectra shift. The unit-cell parameters and volume decreased systematically with increasing pressure, and a reliable isothermal bulk modulus and its pressure derivative were obtained in this study. The third-order Birch-Murnaghan equation of state yielded the isothermal bulk modulus of K-T = 91.5(38) GPa, its pressure derivative K-T' = 4.0(11), and the zero-pressure volume V-o = 524. 2(3) Angstrom(3).