Simulation of the local structure, mixing properties, and stability of Ca$_x$Sr$_{1-x}$CO$_3$ solid solutions by the interatomic potential method

Strontianite (SrCO$_3$)-aragonite (CaCO$_3$) solid solutions have been simulated by the interatomic potential method. The composition dependences of the unit cell parameters, the unit cell volume, and bulk modulus have been constructed. It has been shown that the volume of the unit cell and bulk modulus show small negative deviations from additivity. The local structure of solid solutions has been analyzed. It has been established that the enthalpy of mixing is positive and, for the equimolar composition, reaches a maximum of 2.45 kJ/mol. Based on the composition dependences of the Gibbs free energy for the temperature range of 300–650 K, the solvus of the system has been constructed. According to the obtained data, the solubility of aragonite in strontianite under ambient conditions is 5.5 mol%, while that of strontianite in aragonite is 2.8 mol%. The miscibility gap of the system disappears at around 450 K. The calculated results have been compared with the experimental data.