Pressure-dependent Raman spectra of Ba5(PO4)3Cl alforsite
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The pressure-dependent Raman spectra of synthetic alforsite, Ba5(PO4)3Cl, were investigated up to 34.9 GPa using a DAC at room temperature. During compression to greater than 20 GPa, new Raman active peaks of Ba5(PO4)3Cl were observed. The Raman frequencies of all observed bands for Ba5(PO4)3Cl alforsite increase continuously with increasing pressure. The quantitative analysis of PO4 internal vibrational pressure dependences for different Raman bands in alforsite shows that the ν3 anti-symmetric stretching modes have larger pressure coefficients (from 4.24 to 5.46 cm−1/GPa) whereas, the ν4 anti-symmetric bending vibrations have smaller pressure coefficients (from 1.16 to 2.04 cm−1/GPa). The external modes show larger pressure coefficients (from 4.71 to 5.54 cm−1/GPa). The PO4 internal modes in Ba5(PO4)3Cl alforsite give isothermal mode Grüneisen parameters varying from 0.147 to 0.488, which yields an average PO4 internal mode Grüneisen parameter of 0.314. On the other hand, the external modes give isothermal mode Grüneisen parameters from 1.583 to 2.030. The external modes mainly contribute to the bulk Grüneisen parameter since the bulk thermochemical Grüneisen parameter was determined as 1.44.
KeywordsAlforsite Ba5(PO4)3Cl Raman spectra High pressure
The manuscript was improved by Dr. Terry Mernagh. The authors thank Prof. T. Tsuchiya for his editorial handling. Critical comments and suggestion from two anonymous reviewers are helpful to improve the manuscript. This work was financially supported by National Natural Science Foundation of China (Grant no. 41372040), the Knowledge Innovation Program of the Institute of Geochemistry, Western Light Talents Training Program of Chinese Academy of Sciences, and by National Science and Engineering Research Council of Canada.
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