Thermoelastic properties of magnesiowüstite, (Mg1−xFex)O: determination of the Anderson–Grüneisen parameter by time-of-flight neutron powder diffraction at simultaneous high pressures and temperatures

Ian G Wood, Lidunka Vocadlo, David P Dobson, G David Price, A D Fortes, Frances J Cooper, J W Neale, A M Walker, W G Marshall, M G Tucker, D J Francis, H J Stone, C A McCannon

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Abstract

The ability to perform neutron diffraction studies at simultaneous high pressures
and high temperatures is a relatively recent development. The suitability of this
technique for determining P–V–T equations of state has been investigated by
measuring the lattice parameters of Mg1-xFexO (x = 0.2, 0.3, 0.4), in the range
P < 10.3 GPa and 300 < T < 986 K, by time-of-flight neutron powder diffraction.
Pressures were determined using metallic Fe as a marker and temperatures were
measured by neutron absorption resonance radiography. Within the resolution
of the experiment, no evidence was found for any change in the temperature
derivative of the isothermal incompressibility, ∂KT/∂T, with composition. By
assuming that the equation-of-state parameters either varied linearly or were
invariant with composition, the 60 measured state points were fitted
simultaneously to a P–V–T–x equation of state, leading to values of ∂KT/∂T =-0.024 (9) GPa K-1 and of the isothermal Anderson–Grüneisen parameter ∂T =
4.0 (16) at 300 K. Two designs of simultaneous high-P/T cell were employed
during this study. It appears that, by virtue of its extended pressure range, a
design using toroidal gaskets is more suitable for equation-of-state studies than
is the system described by Le Godec, Dove, Francis, Kohn, Marshall, Pawley,
Price, Redfern, Rhodes, Ross, Schofield, Schooneveld, Syfosse, Tucker & Welch
[Mineral. Mag. (2001), 65, 737–748].

Original languageEnglish
Pages (from-to)886-896
JournalJournal of Applied Crystallography
Volume41
DOIs
Publication statusPublished - 2008

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    Wood, I. G., Vocadlo, L., Dobson, D. P., Price, G. D., Fortes, A. D., Cooper, F. J., Neale, J. W., Walker, A. M., Marshall, W. G., Tucker, M. G., Francis, D. J., Stone, H. J., & McCannon, C. A. (2008). Thermoelastic properties of magnesiowüstite, (Mg1−xFex)O: determination of the Anderson–Grüneisen parameter by time-of-flight neutron powder diffraction at simultaneous high pressures and temperatures. Journal of Applied Crystallography, 41, 886-896. https://doi.org/10.1107/S0021889808025417