Structural change in lead fluorapatite at high pressure

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• 作者：Michael E. Fleet ; Xi Liu and Sean R. Shieh
• 关键词：Lead fluorapatite ; Crystal structure ; Compressibility ; Synchrotron X ; ray diffraction ; Isothermal bulk modulus ; Environment
• 刊名：Physics and Chemistry of Minerals
• 出版年：2010
• 出版时间：January, 2010
• 年：2010
• 卷：37
• 期：1
• 页码：1-9
• 全文大小：513.4 KB

文摘

The structure of lead fluorapatite [PbFAP; Pb₁₀(PO₄)₆F₂], crystallized from the melt in a platinum capsule at 1,000¡ãC and 1 atm, has been investigated by single-crystal X-ray diffraction. Crystal data are a = 9.7638 (6), c = 7.2866 (4) ?, space group P6₃/m, R = 0.043, R _w = 0.034. We have also studied the compressional behaviour of the c-axis channel of PbFAP up to 9 GPa at 25¡ãC, using a diamond-anvil cell, synchrotron X-radiation, and Rietveld powder structure refinement. Pressure–volume data for the channel polyhedron of PbFAP fitted to the third-order Birch–Murnaghan equation resulted in K _T = 33.2 ¡À 1.2 GPa when K _T ′ is fixed at 4. The c-axis channel of PbFAP is about twice as compressible as the unit-cell volume of PbFAP and the channel of calcium apatites. This is attributed to the anomalous narrowing of the channel of PbFAP with increase in confining pressure. Flexibility of the apatite channel is a key factor in the scavenging of toxic heavy metals by calcium apatites.