High Pressure X-Ray Diffraction Study of a Grossular–Andradite Solid Solution and the Bulk Modulus Variation along this Solid Solution

In-situ angle-dispersive x-ray diffraction measurements on three samples of Gr₁₄An₈₄, Gr₃₄An₆₄ and Gr₆₃An₃₄ were performed by using a diamond anvil cell instrument with synchrotron radiation at the Beijing Synchrotron Radiation Facility at up to 13.7 GPa. A least−square fit of the pressure-volume to the Birch–Murnaghan equation of state, when fixed K'₀=4.0 yields bulk modulus values of K₀=166±2, 168±3, 173±2 GPa for Gr₁₄An₈₄, Gr₃₄An₆₄ and Gr₆₃An₃₄, respectively. The bulk modulus increases from 166±2 GPa for Gr₁₄An₈₄ and to 173±2 GPa for Gr₆₃An₃₄ with the increasing An content. Furthermore, by linear interpolation, the bulk modulus of the Gr−An binary system as a function of An content can be expressed as K₀(GPa) =176.9(9)−0.12(1)X_An (R²=0.987).