SIMULATION OF STRUCTURAL PHASE TRANSITION IN NANO3 AND CACO3

Abstract

The order-disorder phase transitions in NaNO3 and CaCO3e simulated by molecular dynamics. The simulations are based on the potentials calculated from the Gordon-Kim modified electron gas formalism extended to molecular ions. We successfully reproduced the transition temperature Tc and the abnormally large c axis thermal expansion observed in experiment. The phase transitions in NaNO3 and CaCO3 were found to be initiated by ±60 and ±180° reorientation of the NO3 and CO3 ions about the c axis. The orientations of NO3 and CO3 ions are continuous with six preferred calcite-type orientations above the phase-transition temperature.