First-principles study of point defects under varied chemical potentials in Li ₄BN ₃H ₁₀

We have employed density functional theory calculations to determine the formation energy for a number of neutral and charged point defects in the mixed anion hydrogen storage compound Li ₄BN ₃H ₁₀, under a variety of chemical potentials, to investigate the possible role of point defects in hydrogen desorption. We discuss the determination of chemical potentials based on four-phase equilibria that arise from the temperature-dependent decomposition reactions. Our results indicate the following: (1) Neutral NH vacancies are nearly always the lowest-energy defect and have a small positive formation energy up to the experimental hydrogen desorption temperature. (2) The cases where NH vacancies are not the lowest energy correspond to unstable four-phase equilibria. (3) Separated pairs of oppositely charged defects are always higher energy than the analogous combined neutral defect.