Behavior of epidote at high pressure and high temperature: A powder diffraction study up to 10 GPa and 1,200 K

G. Diego Gatta, Marco Merlini, Yongjae Lee, Stefano Poli

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Abstract

The thermo-elastic behavior of a natural epidote [Ca1.925 Fe0.745Al2.265Ti0.004Si3.037O12(OH)] has been investigated up to 1,200 K (at 0.0001 GPa) and 10 GPa (at 298 K) by means of in situ synchrotron powder diffraction. No phase transition has been observed within the temperature and pressure range investigated. P-V data fitted with a third-order Birch-Murnaghan equation of state (BM-EoS) give V0 = 458.8(1)Å3, KT0 = 111(3) GPa, and K′ = 7.6(7). The confidence ellipse from the variance-covariance matrix of KT0 and K′ from the least-square procedure is strongly elongated with negative slope. The evolution of the "Eulerian finite strain" vs "normalized stress" yields Fe(0) = 114(1) GPa as intercept values, and the slope of the regression line gives K′ = 7.0(4). The evolution of the lattice parameters with pressure is slightly anisotropic. The elastic parameters calculated with a linearized BM-EoS are: a0 = 8.8877(7) Å, KT0(a) = 117(2) GPa, and K′(a) = 3.7(4) for the a-axis; b0 = 5.6271(7) Å, KT0(b) = 126(3) GPa, and K′(b) = 12(1) for the b-axis; and c0 = 10.1527(7) Å, KT0(c) = 90(1) GPa, and K'(c) = 8.1(4) for the c-axis [KT0(a):KT0(b):KT0(c) = 1.30:1.40:1]. The β angle decreases with pressure, βP(°) = βP0 -0.0286(9)P +0.00134(9)P2 (P in GPa). The evolution of axial and volume thermal expansion coefficient, α, with T was described by the polynomial function: α(T) = α0 + α1T-1/2. The refined parameters for epidote are: α0 = 5.1(2) × 10-5 K-1 and α1 = -5.1(6) × 10-4 K1/2 for the unit-cell volume, α0(a) = 1.21(7) × 10-5 K-1 and α1(a) = -1.2(2) × 10-4 K1/2 for the a-axis, α0(b) = 1.88(7) × 10-5 K-1 and α1(b) = -1.7(2) × 10-4 K1/2 for the b-axis, and α0(c) = 2.14(9) × 10-5 K-1 and α1(c) = -2.0(2) × 10-4 K1/2 for the c-axis. The thermo-elastic anisotropy can be described, at a ry α0(a): α0(b): α0(c) =1'G.D:1.55:1.77. The β angle increases continuously with T, with βT(°) = βT0 + 2.5(1) × 10-4T + 1.3(7) × 10-8T2. A comparison between the thermo-elastic parameters of epidote and clinozoisite is carried out.

Original languageEnglish
Pages (from-to)419-428
Number of pages10
JournalPhysics and Chemistry of Minerals
Volume38
Issue number6
DOIs
Publication statusPublished - 2011 Jun

Bibliographical note

Funding Information:
Carlo Meneghini is acknowledged for the use of the software Scan_Zero, used for integration of translational imaging-plate data, and for helpful discussions. ESRF is thanked for the allocation of beam time. GDG thanks the Italian MIUR (grant no. 2008SPZ743 ). YL thanks the support by Mid-career Researcher Program through NRF grant funded by the Ministry of Education, Science and Technology (MEST) of the Korean Government (No. 2009-0083847). Experiments at PAL were supported in part by MEST and Pohang University of Science and Technology (POSTECH). M. Welch, an anonymous reviewer and the editor M. Rieder are thanked for their suggestions.

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Geochemistry and Petrology

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