Study on intrinsic defects and copper doping in LiAlO2 crystal from combined first-principles and thermodynamic calculations

A large OSL (optically stimulated luminescence) response from copper replacing lithium (Cu-Li) in lithium aluminate (LiAlO2, LAO) has been reported in earlier studies, and the origin of the OSL response was isolated Cu-Li. However, other trapped-hole centers that are not involved in OSL response, such as Cu-Li-V-Li and STH (self-trapped hole center, a hole localized at O ion adjacent to V-Li), also appear in LiAlO2:Cu crystal after irradiation. To reach optimum OSL response of LAO crystal, a comprehensive analysis that integrates first-principles and thermodynamic calculations is employed to investigate the relative stability of intrinsic defects and Cu defects. Defect formation energies (DFE) of these defects are obtained from density functional theory (DFT), as well as corrected by finite-size corrections (FNV). To find the region of Fermi level where the crystal maintains electrical neutrality, we combine DFEs as a function of Fermi level for Cu defects and intrinsic defects to discuss the charge compensation mechanism. Then, the definite DFEs for these defects and the energetically preferred sites for substitutional Cu ions are shown after determining the locations of Fermi levels under different conditions. In O-rich conditions, the results show that Cu-Li is most stable with the decrease of the chemical potential of Al. Furthermore, Cu-Li is energetically preferred under O-poor conditions, and DFE of isolated Cu-Li is much lower than other Cu defects, thus, the optimum OSL signal occurs. To validate our conclusions, we also present the deformation charge density to study the chemical bonds of Li-O, Al-O, Cu-Li-O and Cu-Al-O. The results also suggest that it would cost more energy to destroy Al-O bond than Li-O bond. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study investigates the relative stability and optimal positions of intrinsic defects and Cu defects in LiAlO2 crystal, showing that Cu-Li is most stable in O-rich conditions and energetically preferred under O-poor conditions, leading to the optimum OSL signal. Furthermore, other trapped-hole centers such as Cu-Li-V-Li and STH in the crystal also play a role and need to be considered for overall crystal performance.