The Postspinel Phase Boundary in Mg2 SiO4 Determined by in Situ X-ray Diffraction

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The phase boundary between spinel (gamma phase) and MgSiO3 perovskite + MgO periclase in Mg2 SiO4 was determined by in situ x-ray measurements by a combination of the synchrotron radiation source (SPring-8) and a large multianvil high-pressure apparatus. The boundary was determined at temperatures between 1400[degree sign] to 1800[degree sign]C, demonstrating that the postspinel phase boundary has a negative Clapeyron slope as estimated by quench experiments and thermodynamic analyses. The boundary was located at 21.1 (+/- 0.2) gigapascals, at 1600[degree sign]C, which is [approximate]2 gigapascals lower than earlier estimates based on other high-pressure studies.

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