Different Thermal Stabilities of Cation Point Defects in LaAlO3 Bulk and Films**Supported by the Hebei Provincial Young Top-Notch Talent Support Program under Grant No BJRC2016, the Innovative Funding Project of Graduates of Hebei University under Grant No hbu2018ss62, and the Midwest Universities Comprehensive Strength Promotion Project.

Abstract

Using the first-principles method, we investigate the thermal stability of cation point defects in LaAlO3 bulk and films. The calculated densities of states indicate that cation vacancies and antisites act as acceptors. The formation energies show that cation vacancies are energetically favorable in bulk LaAlO3 under O-rich conditions, while the AlLa antisites are stable in reducing atmosphere. However, the same behavior does not appear in the case of LaAlO3 films. For LaO-terminated LaAlO3 films, La or Al vacancies remain energetically favorable under O-rich and O-deficient conditions. For an AlO2-terminated surface, under O-rich condition the La interstitial atom is repelled from the outmost layer after optimization, which releases more stress leading to the decrease of total energy of the system. An Al interstitial atom has a smaller radius so that it can stay in distorted films and becomes more stable under O-deficient conditions, and the Al interstitial atoms can be another possible carrier source contribution to the conductivity of n-type interface under an ultrahigh vacuum. La and Al antisites have similar formation energy regardless of oxygen pressure. The results would be helpful to understand the defect structures of LaAlO3-related materials.