(Na,Ca)(Ti3+,Mg)Si2O6-clinopyroxenes at high pressure: influence of cation substitution on elastic behavior and phase transition
- Autor(en)
- Angela Ullrich, Ronald Miletich, Tonci Balic-Zunic, Lars Olsen, Fabrizio Nestola, Manfred Wildner, Haruo Ohashi
- Abstrakt
A compressional study of (Na,Ca)(Ti3+,Mg)Si2O6-clinopyroxenes was carried out at high pressures between 10-4 and 10.2 GPa using in situ single-crystal X-ray diffraction, Raman spectroscopy and optical absorption spectroscopy. Compressional discontinuities accompanied by structural changes, in particular, the appearance of two distinct Ti3+-Ti3+ distances within the octahedral chains at 4.37 GPa, provide evidence for the occurrence of a phase transition in NaTi3+Si2O6. Equation-of-state parameters are K 0 = 115.9(7) GPa with K' = -0.9(3) and K 0 = 102.7(8) GPa with K' = 4.08(5) for the low- and high-pressure range, resp. The transition involves a C2/c-P symmetry change, which can be confirmed by the occurrence of new modes in Raman spectra. Since no significant discontinuity in the evolution of the unit-cell vol. with pressure has been obsd., the transition appears to be second-order in character. The influence of the coupled substitution Na+Ti3+.tautm.Ca2+Mg2+ on the static compression behavior and the structural stability has been investigated using a sample of the intermediate compn. (Na0.54Ca0.46)(Mg0.46Ti0.54)Si2O6. No evidence for a deviation from continuous compression behavior has been found, neither in lattice parameter nor in structural data and the fit of a third-order Birch-Murnaghan equation-of-state to the pressure-vol. data yields a bulk modulus of K 0 = 109.1(5) GPa and K' = 5.02(13). Raman and polarized absorption spectra have been compared to NaTiSi2O6 and reveal major similarities. The main driving force for the phase transition in NaTi3+Si2O6 is the localization of the Ti3+ d-electron and the accompanying distortion, which is suppressed in the (Na,Ca)(Ti3+,Mg)Si2O6-clinopyroxene.
- Organisation(en)
- Institut für Mineralogie und Kristallographie
- Externe Organisation(en)
- Universität Heidelberg, University of Copenhagen, Università degli Studi di Padova, HASHI Institute for Silicate Science
- Journal
- Physics and Chemistry of Minerals
- Band
- 37
- Seiten
- 25-43
- Anzahl der Seiten
- 19
- ISSN
- 0342-1791
- Publikationsdatum
- 2010
- Peer-reviewed
- Ja
- ÖFOS 2012
- 105113 Kristallographie, 1030 Physik, Astronomie
- Link zum Portal
- https://ucrisportal.univie.ac.at/de/publications/3cd5154b-180e-41b5-af8f-648a7b283dbe