RESUMO
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 VLi-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 Lii+1 interstitial defect providing compensation at low temperatures and the VO2+ vacancy defect occurring close to the Li2O saturation limit.
RESUMO
Octalithium ceramics with their high stoichiometric concentration of lithium offer exceptionally high tritium breeding ratios in comparison with other candidate breeder materials for tokamak fusion reactors, this is especially true with incorporation of a neutron multiplier into the crystal structures. Although, there are concerns surrounding the stability of these materials at operational temperatures. Therefore in this paper, we explore the thermodynamic properties of a selection of candidate octalithium ceramics in low and high temperature regimes (0-1200 K) using density functional perturbation theory. Enthalpies as well as Gibbs formation energies were used to distinguish candidates which may or may not be susceptible to degradation.
