Decomposition of lithium hydride-deuteride (LiH1-xDx), and the impact of isotopic abundance

The decomposition behaviour of lithium hydride-deuteride (LiH1-xDx) is of critical interest for nuclear fusion breeder materials and hydrogen storage applications. In this study, we develop and apply a comprehensive multiscale computational framework that combines density functional theory (DFT), phonon analysis and quasi-random structural modelling to evaluate the thermodynamic stability and selective isotope behaviours across a range of H:D compositions. A key feature of this work lies in the dual pathway modelling of gas evolution, considering both isotopically distinct (H2 & D2) and mixed (HD) product formation, which reveals a non-linear decomposition temperature profile with a minimum at equiatomic ratios, driven by entropic and zero-point energy effects. Additionally, we introduce a composition-dependant model for isotope selective decomposition, demonstrating that hydrogen-rich systems decompose at significantly lower temperatures than their deuterium-rich counterparts, due to mass-induced bond weakening and lattice destabilisation. These insights result in a predictive thermodynamic map of LiH1-xDx decomposition, enabling tailored design of breeder materials and informing isotope separation methodologies for fusion applications. This work establishes a link between atomic scale isotopic variation and macro scale decomposition behaviour.