Elasticity of single‐crystal forsterite measured to 1700 K

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Abstract
Measurements of the nine adiabatic elastic constants of single‐crystal forsterite are reported for the temperature range 300–1700 K at ambient pressure. The measured room temperature Cijs and their first temperature derivatives at ambient conditions are generally consistent with previous measurements, which were taken over a narrower temperature range. Slight nonlinear behavior is observed in the temperature dependence of the C11s, C22s, and C33s moduli. The resulting Hill‐averaged bulk and rigidity moduli Ks and G are lower at 1700 K than predicted by linear extrapolation of low‐temperature data. At 1700 K the new data give Ks = 103.8 ± 1.1 GPa and G = 61.3 ± 0.5 GPa. Isotropic elastic wave velocities have been calculated using the Hill averaging scheme over the range of temperatures measured. At T = 1700 K and ambient pressure we find vp = 7.79 ± 0.04 km s−1 and vs = 4.48 ± 0.03 km s−1. The parameter (∂ℓnvs/∂ℓnvp)P is near to 1.2 and independent of temperature. Calculations are presented for elastic properties and other parameters important for the equations of state and anharmonicity of forsterite. Recent high‐temperature thermal expansion measurements on a forsterite specimen from the same boule are used in this analysis. Effects of uncertainties in high‐temperature thermal expansion data on these parameters have been evaluated and are discussed.