AL, GE ORDERING IN ALUMINOGERMANATE SODALITES - A MONTE-CARLO STUDY

The distribution of Ge and Al atoms on the framework of aluminogermanate sodalites is analyzed by Monte Carlo simulations. Several thermodynamic (configurational energy, entropy, free energy) and structural (fraction of antisites, pair correlation functions) variables are studied as a function of temperature in the range from 600 to 1200 K. Results obtained by using long-range electrostatic interactions are compared with those yielded by a lattice-gas model with short-range interactions. The inclusion of long-range terms in the interatomic potential modifies appreciably the studied thermodynamic variables, especially for temperatures higher than 900 K. For T < 700 K, the atom ordering can be described reasonably well by a mean-field approximation.