X-ray single-crystal structural characterization of Na2MgSiO4 with cristobalite-type structure synthesised at 22 GPa and 1800 °C

Abstract

Na 2 MgSiO 4 is a mineralogical phase known in the literature as N2MS and reported in several high-pressure experiments (13.6 P PT Na 2 MgSiO 4 is known, a structural study of the phase recovered in high-pressure experiments has not been done yet. Here we present a chemical and structural study of a crystal of Na 2 MgSiO 4 synthesised in the model system Na 2 MgSiO 4 –Mg 2 SiO 4 at 22 GPa and 1800 °C. The compound was found to crystallize with the orthorhombic cristobalite-type structure previously described at room conditions, space group Pna 2 1 , with lattice parameters a = 10.8193(8), b = 5.2702(3), c = 7.0598(4) A, V = 402.55(4) A 3 , and Z = 4. The structure was refined to R 1 = 0.0184 using 644 observed reflections [ F o > 4σ( F o )] and 73 parameters. The unit-cell of the phase studied here is nearly identical to that of Na 2 MgSiO 4 synthesised at room conditions, thus indicating that it likely relaxed during the pressure release occurring during quenching.