Single-crystal neutron-diffraction study of pyrope in the temperature range 30-1173 K

Single-crystal neutron-diffraction data collected from a pyrope crystal from the Dora Maira Massif, Western Alps, Italy, expands the structure analysis of synthetic end-member pyrope over a wide T range. The atomic displacement properties were analysed by the higher cumulant model in the Gram-Charlier series approximation and show that the anharmonic contribution to the dynamic part of the Mg site displacement is significant above 700 K. No evidence was found for static site disorder in the dodecahedral Mg site by refinement with split-atom models, and the intercept at 0 K resulting from linear interpolation of the high-T harmonic displacement coefficients is not statistically significant. The refinement of high-order displacement-tensor components results in significantly lower figures of merit in the whole explored T range.