The Study of Crystal Structure on Grossular-Andradite Solid Solution

The effects of Al3+-Fe3+ substitution on 10 synthesized garnet samples along the grossular-andradite binary solid solution were investigated using both powder and single-crystal X-ray diffraction. Results showed that cell volume increased with andradite content. Small negative excess volume was observed in the Al-rich samples. By measuring the bond length, polyhedral volume, octahedral distortion parameter (sigma), and tetrahedral rotation angle (alpha), we determined that the distortion occurred on the dodecahedral site. The width of the diffraction peaks was obviously related to the composition of the solid solution. Full width at half maximum of diffraction peaks was used to calculate the microstrain, which may have a relationship with enthalpy of mixing.