A study was made of self-diffusion along the a- and b-axes of synthetic Fe-free diopside monocrystals at temperatures ranging from 1273 to 1653K. The 44Ca diffusion profiles were measured by means of -particle Rutherford back-scattering spectrometric micro-analysis. Two distinct diffusional regimes were identified that were characterized by activation enthalpies of 280 and 951kJ/mol, below and above 1515K, respectively. The change in diffusion regime occurred near to the onset of pre-melting, and was explained in terms of the enhanced creation of Frenkel point defects with an activation enthalpy for formation of 1524kJ/mol. It was concluded that, if this explanation were correct, the Ca Frenkel point defect concentration could attain several mol% when close to the melting point.

Premelting and High-Temperature Diffusion of Ca in Synthetic Diopside: an Increase of the Cation Mobility. A.Dimanov, J.Ingrin: Physics and Chemistry of Minerals, 1995, 22[7], 437-42