Synthetic Lead Bromapatite: X-ray Structure at Ambient Pressure and Compressibility up to about 20 GPa
Lead bromapatite [Pb{sub 10}(PO{sub 4}){sub 6}Br{sub 2}] has been synthesized via solid-state reaction at pressures up to 1.0 GPa, and its structure determined by single-crystal X-ray diffraction at ambient temperature and pressure. The large bromide anion is accommodated in the c-axis channel by lateral displacements of structural elements, particularly of Pb2 cations and PO{sub 4} tetrahedra. The compressibility of bromapatite was also investigated up to about 20.7 GPa at ambient temperature, using a diamond-anvil cell and synchrotron X-ray radiation. The compressibility of lead bromapatite is significantly different from that of lead fluorapatite. The pressure-volume data of lead bromapatite (P < 10 GPa) fitted to the third-order Birch-Murnaghan equation yield an isothermal bulk modulus (K{sub T}) of 49.8(16) GPa and first pressure derivative (K{sub T}) of 10.1(10). If K{sub T} is fixed at 4, the derived K{sub T} is 60.8(11) GPa. The relative difference of the bulk moduli of these two lead apatites is thus about 12%, which is about two times the relative difference of the bulk moduli ({approx}5%) of the calcium apatites fluorapatite [Ca{sub 10}(PO{sub 4}){sub 6}F{sub 2}], chlorapatite [Ca{sub 10}(PO{sub 4}){sub 6}Cl{sub 2}] and hydroxylapatite [Ca{sub 10}(PO{sub 4}){sub 6}(OH){sub 2}]. Another interesting feature apparently related to the replacement of F by Br in lead apatite is the switch in the principle axes of the strain ellipsoid: the c-axis is less compressible than the a-axis in lead bromapatite but more compressible in lead fluorapatite.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- Sponsoring Organization:
- USDOE SC OFFICE OF SCIENCE (SC)
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 1042052
- Report Number(s):
- BNL-97730-2012-JA; PCMIDU; TRN: US201212%%463
- Journal Information:
- Physics and Chemistry of Minerals, Vol. 38, Issue 5; ISSN 0342-1791
- Country of Publication:
- United States
- Language:
- English
Similar Records
Structural Change in Lead Fluorapatite at High Pressure
Single-crystal X-ray diffraction of fluorapatite to 61 GPa