The high-pressure and temperature equation of state of a majorite solid solution in the system of Mg 4 Si 4 O 12 -Mg 3 Al 2 Si 3 O 12

Abstract

The high-pressure and temperature equation of state of majorite solid solution, Mj0.8Py0.2, was determined up to 23 GPa and 773 K with energy-dispersive synchrotron X-ray diffraction at high pressure and high temperature using the single- and double-stage configurations of the multianvil apparatuses, MAX80 and 90. The X-ray diffraction data of the majorite sample were analyzed using the WPPD (whole-powder-pattern decomposition) method to obtain the lattice parameters. A least-squares fitting using the third-order Birch-Murnaghan equation of state yields the isothermal bulk modulus, K T0 = 156 GPa, its pressure derivative, K′ = 4.4(±0.3), and temperature derivative (∂K T /∂T) P = −1.9(±0.3)× 10−2 GPa/K, assuming that the thermal expansion coefficient is similar to that of pyrope-almandine solid solution.