New thermoelastic parameters of natural <Emphasis Type="Italic">C</Emphasis>2/<Emphasis Type="Italic">c</Emphasis> omphacite |
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| Authors: | Email author" target="_blank">Francesco?PandolfoEmail author Fabrizio?Nestola Fernando?Cámara M?Chiara?Domeneghetti |
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| Institution: | 1.Dipartimento di Scienze della Terra e dell’Ambiente,Università di Pavia,Pavia,Italy;2.Dipartimento di Geoscienze,Università di Padova,Padua,Italy;3.Dipartimento di Scienze della Terra,Università degli Studi di Torino,Torino,Italy |
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| Abstract: | The compressibility at room temperature and the thermal expansion at room pressure of two disordered crystals (space group
C2/c) obtained by annealing a natural omphacite sample (space group P2/n) of composition close to Jd56Di44 and Jd55Di45, respectively, have been studied by single-crystal X-ray diffraction. Using a Birch–Murnaghan equation of state truncated
at the third order BM3-EoS], we have obtained the following coefficients: V
0 = 421.04(7) Å3, K
T0 = 119(2) GPa, K′ = 5.7(6). A parameterized form of the BM3 EoS was used to determine the axial moduli of a, b and c. The anisotropy scheme is β
c
≤ β
a
≤ β
b
, with an anisotropy ratio 1.05:1.00:1.07. A fitting of the lattice variation as a function of temperature, allowing for linear
dependency of the thermal expansion coefficient on the temperature, yielded αV(1bar,303K) = 2.64(2) × 10−5 K−1 and an axial thermal expansion anisotropy of α
b
≫ α
a
> α
c
. Comparison of our results with available data on compressibility and thermal expansion shows that while a reasonable ideal
behaviour can be proposed for the compressibility of clinopyroxenes in the jadeite–diopside binary join K
T0 as a function of Jd molar %: K
T0 = 106(1) GPa + 0.28(2) × Jd(mol%)], the available data have not sufficient quality to extract the behaviour of thermal expansion for the same binary join in
terms of composition. |
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