High-pressure X-ray study of LiCrSi2O6 clinopyroxene and the general compressibility trends for Li-clinopyroxenes |
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Authors: | Benedetta Periotto Ross J. Angel Fabrizio Nestola Tonci Balić-Žunić Cinzia Fontana Daria Pasqual Matteo Alvaro Günther J. Redhammer |
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Affiliation: | 1. Department of Geography and Geology, University of Copenhagen, ?ster Voldgade 10, 1350, Copenhagen, Denmark 8. Dipartimento di Geoscienze, Università degli Studi di Padova, via Gradenigo 6, 35131, Padova, Italy 2. Department of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24061-0420, USA 3. Dipartimento di Geoscienze, Università degli Studi di Padova, via Gradenigo 6, 35131, Padova, Italy 4. Danish Natural History Museum, University of Copenhagen, ?ster Voldgade 5-7, 1350, Copenhagen, Denmark 5. Dipartimento di Scienze Chimiche, Università degli Studi di Padova, via Marzolo 1, 35131, Padova, Italy 6. International Research School of Planetary Sciences Dipartimento di Scienze Umanistiche e della Terra, Università G. D’Annunzio Chieti-Pescara, via dei Vestini 31, 66013, Chieti, Italy 7. Division of Mineralogy, Department of Materials Engineering and Physics, University of Salzburg, Hellbrunnerstrasse 34, 5020, Salzburg, Austria
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Abstract: | High-pressure single-crystal X-ray diffraction measurements of synthetic LiCrSi2O6 clinopyroxene (with space group P21/c) were performed in a diamond-anvil cell up to 7.970 GPa. No phase transition has been observed within the pressure range investigated, but the elastic behavior at lower pressures (up to ~2.5 GPa) is affected by an anomalous softening due to the proximity of the phase transition to the HT-C2/c phase at 330 K and at ambient pressure. A third-order Birch–Murnaghan equation of state fitted to the compression data above 2.5 GPa yields a bulk modulus K T0 = 93(2) GPa and its first derivative K′ = 8.8(6). The structural data measured up to 7.970 GPa confirm that the space group P21/c is maintained throughout the whole pressure range investigated. The atomic parameters, obtained from the integrated diffraction intensities, suggest that the Li coordination polyhedron changes its coordination number from 5 to 6 at 6–7 GPa by means of the approach of the bridging O atom, related to the increased kinking of the B tetrahedral chain. Furthermore, at higher pressures, the structural evolution of LiCrSi2O6 provides evidence in the variation of kinking angles and bond lengths of a potential phase transition above 8 GPa to the HP-C2/c space group. A comparison of the Li-clinopyroxenes (M1 = Cr, Al, Sc, Ga, Mg + Fe) previously investigated and our sample shows that their elastic behavior and structural mechanisms of compression are analogous. |
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