Microscopic strain in synthetic pyrope-grossular solid solutions determined by synchrotron X-ray powder diffraction at 5 K; the relationship to enthalpy of mixing behavior

An analysis of the X-ray reflection profiles for a series of synthetic pyrope-grossular garnets, based on theoretical considerations of X-ray line broadening, allows for the first time a direct determination of crystallite size and the root-mean-square structural strain for a mineral solid solution. The measured microscopic strain shows positive and symmetric deviation from linearity across the join, with the largest excess in pyrope-rich compositions. There is a good correlation between the structural strain and the macroscopic enthalpy of mixing behaviour for this garnet solid solution as measured by calorimetry.