Atomistic computer modelling techniques were applied to study the intrinsic defects in the Y2SiO5 (YSO) and Lu2SiO5 (LSO) structures at 0 and 300 K temperatures. The approach used is based on the interatomic potentials model and lattice energy minimization. A set of potential parameters were obtained by empirical adjustment and reproduced the lattice parameters with values better than 0.98% and 2.24% for YSO and LSO, respectively. Intrinsic defects were performed using the well-known Mott-Littleton method. Two conditions were adopted to calculate defects: for unbonded condition, point defects (vacancies and interstitials) were calculated without possible interactions with each other; for bounded condition, point defects interact with each other through coulomb and short-range potentials. All possible configurations were tested for Frenkel and Schottky defects in unbounded condition and only the most favourable defect configuration was considered in bounded condition. Oxygen Frenkel type is the most favourable energetic defect in both structures at both temperatures. Bounded defects calculations showed that oxygen vacancy and interstitial located in first coordinate sphere have the lowest solution energy values for LSO. However, the most favourable defect positions are further apart in the YSO structure. The bounded condition was most favourable decreasing the energetic costs of the defect for all cases demonstrating that the interaction of O Frenkel pair should be consider in future works.
CaYAl3O7 presents a challenge for computer modelling techniques because of its site-occupancy disorder related to the Ca/Y shared site. Supercells were built to reproduce experimental results which have the best agreement and lowest lattice energy. The potential parameters were obtained by empirical fitting, and reproduced the structure to within 1.09%. Results obtained by supercell and the Mott-Littleton methods were compared. Both methods predict oxygen Frenkel defects are likely to be formed.
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