X-ray single-crystal structural characterization of Na2MgSiO4 with cristobalite-type structure synthesised at 22 GPa and 1800oCстатья
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Дата последнего поиска статьи во внешних источниках: 24 октября 2018 г.
Аннотация:Na2MgSiO4 is a high-pressure phase known in the literature as N2MS and reported in several experiments to coexist with wadsleyite, garnet and pyroxene at 13.6–22 GPa. Although the ease to produce such a synthetic phase, its crystal structure has never been elucidated yet. Here we present the first chemical and structural study of a crystal of Na2MgSiO4 synthesized in the model system Na2MgSiO4–Mg2SiO4 at 22 GPa and 1800 °C. The compound was found to crystallize with the orthorhombic cristobalite-type structure, space group Pna21, with lattice parameters a = 10.8193(8), b = 5.2702(3), c = 7.0598(4) Å, V = 402.55(4) Å3, and Z = 4. The structure was refined to R1 = 0.0184 using 644 observed reflections [Fo > 4σ(Fo)] and 73 parameters. The structural characterization of the high-pressure Na2MgSiO4 phase is important, because the study of its thermodynamic constants provides new constraints on thermobarometry of the upper mantle assemblages.