| Title | Compressibility of carbonophosphate bradleyite Na3Mg(CO3)(PO4) by X-ray diffraction and Raman spectroscopy |
| Authors | Gao, Jing Huang, Weifeng Wu, Xiang Fan, Dawei Wu, Ziyu Xia, Dingguo Qin, Shan |
| Affiliation | Peking Univ, Sch Earth & Space Sci, Key Lab Orogen Belts & Crustal Evolut, MOE, Beijing 100871, Peoples R China. Univ Sci & Technol China, Natl Synchrotron Radiat Lab, Hefei 230029, Peoples R China. Peking Univ, Coll Engn, Beijing 100871, Peoples R China. Chinese Acad Sci, Inst Geochem, Lab High Temp & High Pressure Study Earths Interi, Guiyang 550002, Peoples R China. |
| Keywords | Carbonates Phosphates Compressibility Diamond anvil cell HIGH-PRESSURE PHASE EQUATION-OF-STATE DEEP CARBON-CYCLE CRYSTAL-STRUCTURE LOWER MANTLE VIBRATIONAL BEHAVIOR TRICALCIUM PHOSPHATE SOLID-SOLUTION EARTHS MANTLE FLUORAPATITE |
| Issue Date | 2015 |
| Publisher | physics and chemistry of minerals |
| Citation | PHYSICS AND CHEMISTRY OF MINERALS.2015,42,(3),191-201. |
| Abstract | Bradleyite Na3Mg(CO3)(PO4) is one typical carbonophosphate, representing dual properties of both carbonates and phosphates. Compressibility of bradleyite has been investigated using synchrotron radiation X-ray diffraction and Raman spectroscopy combined with diamond anvil cells up to 41 GPa at room temperature. Experimental results clearly demonstrate that bradleyite is stable in the investigated pressure conditions. Isothermal pressure-volume relationship has been fitted to the third-order Birch-Murnaghan equation of state with K (0) = 65.9(9) GPa, K (0) ' = 3.08(3) and V (0) = 301.4(4) (3). The crystallographic axes exhibit similar and considerable compressibility up to 16 GPa, but an increasing anisotropy can be defined thereafter because the b-axis becomes more and more rigid. Insight into the behaviors of [PO4](3-) and [CO3](2-) groups have been obtained using Raman spectroscopy, with the symmetrical stretching bands being observed at 970.8 and 1,078.7 cm(-1), respectively. Both modes shift to higher frequencies on compression. The pressure coefficient of Raman shifts in C-O is 3.18(2) x 10(-3) cm(-1)/GPa, and the value of Gruneisen parameters (gamma) is 0.22. [PO4](3-) groups in bradleyite exhibit a mode hardening, with a slope of 3.54(6) x 10(-3) cm(-1)/GPa, gamma = 0.24 below 16 GPa, and of 2.37(1) x 10(-3) cm(-1)/GPa, gamma = 0.16 thereafter. The mode hardening may indicate correlations to the increase in symmetry of the local environment around the [PO4] tetrahedra. The low gamma values are compatible with the rigidness of [CO3](2-) and [PO4](3-) in bradleyite, which have, respectively, been documented in carbonates and phosphates. Our present study may open new perspectives on the Earth carbon and phosphorus cycle, arouse the interest in carbonophosphate minerals, and shed light on other [CO3](2-) and [PO4](3-) coexistent phases. |
| URI | http://hdl.handle.net/20.500.11897/155329 |
| ISSN | 0342-1791 |
| DOI | 10.1007/s00269-014-0710-0 |
| Indexed | SCI(E) EI |
| Appears in Collections: | 地球与空间科学学院 工学院 造山带与地壳演化教育部重点实验室 |
