Thermoelastic equation of state of jadeite NaAlSi sub(2)O sub(6): An energy-dispersive Reitveld Refinement Study of low symmetry and multiple phases diffraction

We report the first measurement of a complete set of thermoelastic equation of state of a clinopyroxene mineral. We have conducted an in situ synchrotron x-ray diffraction study of jadeite at simultaneous high pressures and high temperatures. A modified Rietveld profile refinement program has been applied to refine the diffraction spectra of low symmetry and multiple phases observed in energy dispersive mode. Unit cell volumes, measured up to 8.2 GPa and 1280 K, are fitted to a modified high-temperature Birch-Murnaghan equation of state. The derived thermoelastic parameters of the jadeite are: bulk modulus K=125 GPa with assumed pressure derivative of bulk modulus K' = partial differential K/ partial differential P = 5.0, temperature derivative of bulk modulus and volumetric thermal expansivity [alpha] = a + bT with values of a=2.5610 super(-5)K super(-1) and b=0.26x10 super(-8) K super(-2). We also derived thermal Grueneisen parameter [gamma] sub(th)=1.06 for ambient conditions; Anderson-Grueneisen parameter [delta] sub(To)=5.02, and pressure derivative of thermal expansion partial differential [alpha]/ partial differential P = -1.0610 super(-6) K super(-1) GPa super(-1). From the P-V-T data and the thermoelastic equation of state, thermal expansions at five constant pressures of 1.0, 2.5, 4.0, 5.5, and 7.5 GPa are calculated. The derived pressure dependence of thermal expansion is: Delta [alpha]/ Delta P = -0.9710 super(-6)K super(-1)GPa super(-1), in good agreement with the thermodynamic relations.