Elastic behaviour and structural evolution of topaz at high pressure |
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| Authors: | G Diego Gatta F Nestola T Boffa Ballaran |
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| Institution: | (1) Dip. Scienze della Terra, Sez. Mineralogia, Universita’ degli Studi di Milano, Via Botticelli, 23, 20133 Milano, Italy;(2) Bayerisches Geoinstitut, Universität Bayreuth, Universität Str. 30, 95447 Bayreuth, Germany;(3) Crystallography Laboratory, Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA |
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| Abstract: | The elastic behaviour and the high-pressure structural evolution of a natural topaz, Al2.00Si1.05O4.00(OH0.26F1.75), have been investigated by means of in situ single-crystal X-ray diffraction up to 10.55(5) GPa. No phase transition has been observed within the pressure range investigated. Unit-cell volume data were fitted with a third-order Birch-Murnaghan Equation of State (III-BM-EoS). The III-BM-EoS parameters, simultaneously refined using the data weighted by the uncertainties in P and V, are: V
0=345.57(7) Å3, K
T0=164(2) GPa and K′=2.9(4). The axial-EoS parameters are: a
0=4.6634(3) Å, K
T0(a)=152(2) GPa, K′(a)=2.8(4) for the a-axis; b
0=8.8349(5) Å, K
T0(b)=224(3) GPa, K′(b)=2.6(6) for the b-axis; c
0=8.3875(7) Å, K
T0(c)=137(2) GPa, K′(c)=2.9(4) for the c-axis. The magnitude and the orientation of the principal Lagrangian unit-strain ellipsoid were determined. At P−P
0=10.55 GPa, the ratios ε1:ε2:ε3 are 1.00:1.42:1.56 (with ε1||b, ε2||a, ε3||c and |ε3| > |ε2| > |ε1|). Four structural refinements, performed at 0.0001, 3.14(5), 5.79(5) and 8.39(5) GPa describe the structural evolution in terms of polyhedral distortions. |
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| Keywords: | Topaz High-pressure Single crystal X-ray diffraction Compressibility Structural evolution |
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