Effect of La doping on the structural stability and hydrogen adsorption behavior of Ce-La alloys

As a non-radioactive surrogate, Ce metal and its alloy have been used as the substitutional material to study the physical and chemical behavior of Pu alloys. Ce metal is prone to hydrogen reaction when exposed to the ambient atmosphere at room temperature, resulting in changes to the microstructure and mechanical properties of the Ce metal. It has been observed that the hydrogenation behavior of Ce-based alloys is influenced by concentration and distribution of La dopants. However, the understanding of intrinsic influence mechanism of the La element on the hydrogenation characteristics and behavior of Ce-based alloys remains incomplete. In this work, the evolution of atomic and electronic structure of Ce alloy with increasing La concentrations from 1 to 10 at% is investigated by first-principle calculations based on density functional theory (DFT). In addition to bulk properties, the impact of different concentrations and locations of La doping on surface energy is analyzed as well. Furthermore, the effects of La doping on multiple characteristics of Ce-La (111) surface are investigated, including adsorption energy, electronic structure, hydrogen molecular adsorption and dissociation, and charge transfer. Compared to the surface of pure Ce, the surface of Ce-La has an enhanced hydrogen adsorption energy, a higher degree of charge transfer, increased stability in H ₂ molecular adsorption, and stronger orbital hybridization. This observation indicates that the chemisorption process between H atoms and Ce-La surface atoms will results in a greater electron loss on the metal atoms of the Ce-La surface, which makes the Ce-La surface more susceptible to hydrogenation-induced corrosion. This work provides a physical image for the chemisorption process of Ce-La-H and theoretical evidence for evaluating the adequacy and limitation of Ce-La alloys as surrogates for Pu-Ga alloys.