Thermodynamic properties of ordered CsCl-type intermetallic compounds from Monte Carlo simulations

Monte Carlo results for the partial thermodynamic properties and the long-range order parameter of ordered CsCl-type intermetallic compounds are presented and are compared with those obtained from the zeroth (Bragg-Williams) approximation. The model chosen is a rigid bcc lattice with nearest-neighbour central pairwise interactions. The simulations have been carried out at two reduced temperatures, T T_c = 0.9 and 0.7143. The results for all the partial thermodynamic properties obtained from the two-sublattice model in the zeroth approximation are found to agree well with those obtained from the Monte Carlo simulations at compositions close to stoichiometry. Further away from stoichiometry, however, the results for the partial energy and entropy differ significantly, although these differences approximately compensate, making the results for the partial free energy agree quite well over a wide composition range. It is also found that the position of the second order phase transition boundary can be determined reliably from the strong singularity in the partial energy as an alternative to obtaining its position from the weak singularity in the chemical potential.