High-Temperature Intrinsic Defect Chemistry of Li₈PbO₆ Ceramic Breeding Material

Understanding the intrinsic defect chemistry of tritium breeder materials proposed for use in future fusion reactors is imperative, as certain defects may act as traps leading to retention of tritium in the ceramic matrix. In this paper, we use combined density functional theory simulations with simple thermodynamics to explore the intrinsic defect chemistry of octalithium plumbate (Li₈PbO₆) as a function of both temperature and oxygen partial pressure. Importantly, we consider vibrational contributions to the energies of the reference states used in the calculations of the defect formation energies. Our results indicate that including these temperature effects can modify the predicted defect chemistry for materials at a high temperature. For Li₈PbO₆, the defect chemistry is predicted to be dominated by the V_Li^-1 defect, which will likely act as a trap for tritium. The charge compensating mechanism is predicted to change as a function of the conditions, with the Li⁺¹ interstitial defect providing compensation at low temperatures and the V_O²⁺ vacancy defect occurring close to the Li₂O saturation limit.