Structural and vibrational behaviour of fluorapatite with pressure. Part II: in situ micro-Raman spectroscopic investigation |
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Authors: | P Comodi Yu Liu M L Frezzotti |
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Institution: | (1) Dipartimento di Scienze della Terra, Università di Perugia, Piazza Università, 06100 Perugia, Italy Tel.: +39-075-5852656; Fax: +39-075-5852603 e-mail: Comodip@unipg.it, IT;(2) Wuhan Institute of Chemical Technology, Wuhan, 430074 Hubei, PR China, CN;(3) Dipartimento di Scienze della Terra, Via Laterina 8, 53100 Siena, Italy, IT |
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Abstract: | High-pressure Raman investigations were carried out on a synthetic fluorapatite up to about 7 GPa to analyse the behaviour
of the phosphate group's internal modes and of its lattice modes. The Raman frequencies of all modes increased with pressure
and a trend toward reduced splitting was observed for the PO4-stretching modes (ν3a(Ag) and ν3b(Ag); ν3a(E2g) and ν3b(E2g)] and the PO4 out-of-plane bending modes ν4a(Ag) and ν4b(Ag)]. The pressure coefficients of phosphate modes ranged from 0.0047 to 0.0052 GPa−1 for ν3, from 0.0025 to 0.0044 GPa−1 for ν4, from 0.0056 to 0.0086 GPa−1 for ν2 and 0.0046 for ν1 GPa−1, while the pressure coefficients of lattice modes ranged from 0.0106 to 0.0278 GPa−1. The corresponding Grüneisen parameters varied from 0.437 to 0.474, 0.428, 0.232 to 0.409 and 0.521 to 0.800 for phosphate
modes ν3, ν1, ν4, ν2, respectively, and from 0.99 to 2.59 for lattice modes. The vibrational behaviour was interpreted in view of the high-pressure
structural refinement performed on the same crystal under the same experimental conditions. The reduced splitting may thus
be linked to the reduced distortion of the environment around the phosphate tetrahedron rather than to the decrease of the
tetrahedral distortion itself. Moreover, the amount of calcium polyhedral compression, which is about three times the compression
of phosphate tetrahedra, may explain the different Grüneisen parameters.
Received: 25 April 2000 / Accepted: 20 December 2000 |
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Keywords: | Apatite Micro-Raman spectroscopy High pressure |
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