Mechanisms of phase transitions between Al2SiO5 polymorphs
Samtsevich A. I., Oganov A. R.
Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2021. V. 150. N 5. P. 79-91
https://doi.org/10.31857/S0869605521050051
Language: English
Abstract
In nature Al2SiO5 exists as three polymorphs: kyanite, andalusite and sillimanite, often coexisting in the same rock. Here, we have studied in detail the mechanisms of structural transitions between all three phases of Al2SiO5 – kyanite-andalusite, andalusite-sillimanite and kyanite-sillimanite at the pressures of 0 and 10 GPa. The phase transition pathways with the lowest energy barriers are found by constructing a number of geometrically likeliest pathways and optimizing them using the variable-cell nudged elastic band method (VCNEB). We have analyzed the structural changes along the obtained lowest-energy pathways. These results have provided insights into the nature of structural relationships between Al2SiO5 polymorphs, their coexistence with each other and their transformation pathways. In particular, we confirm that phase transition barriers are very high, which allows these phases to coexist during geological timescales – thus serving as geothermobarometers.
Keywords: Al2SiO5 polymorphs, phase transitions mechanisms, density functional theory
