Computational modelling of intrinsic defects in the orthosilicates Y₂SiO₅ and Lu₂SiO₅

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.