Compressibility of phase A, Mg₇Si₂H₆O₁₄ up to 11.2 GPa

Abstract

A single crystal high-pressure X-ray diffraction study of phase A was performed using a diamond anvil cell up to 11.2 GPa at ambient temperature. The chemical formula of this sample, determined by EPMA from an average of 18 data points, was Mg_6.99Si_1.99H_6.06O₁₄. Axial linear compressibilities of phase A were β_a=2.92(2) and β_c=2.17(3) (×10^-3/GPa). The isothermal bulk modulus, calculated using the Birch-Murnaghan equation of state, was K_T0=105(4) GPa with a pressure derivative K′=3.9(8) and V₀=512.2(6) ų. The bulk modulus correlates with the summation of the filling factor of the tetrahedral site and the octahedral site, as shown for the minerals on the forsterite-brucite join in the system MgO-SiO₂-H₂O.