Competing hydrogenation pathways to metastable CaH6 revealed by machine learning potential molecular dynamics

Le résumé fourni par la source

The synthesis of the high- T c superhydride CaH 6 has stimulated significant interest in understanding synthesis pathways for metastable hydrides. However, the microscopic mechanisms governing such hydrogenation reactions remain poorly understood. Here, we show that machine-learning potential molecular dynamics simulations can reproduce and distinguish competing reaction pathways leading to metastable and stable hydrides. By simulating hydrogenation reactions at CaH 2 / H 2 and CaH 4 / H 2 interfaces, we identify two distinct pathways that produce clathrate-type CaH 6 and A15-type CaH 5.75 , respectively. CaH 5.75 lies on the convex hull but requires extensive Ca sublattice rearrangement and therefore forms only at elevated temperatures. In contrast, CaH 6 becomes kinetically accessible when CaH 2 is used as the precursor. The crystallographic compatibility between the Ca sublattice of CaH 2 and the body-centered cubic framework of CaH 6 enables a martensitic-like topotactic transformation that bypasses the reconstructive pathway leading to CaH 5.75 . These results reveal how precursor structure and thermodynamic stability compete to determine superhydride formation pathways and demonstrate that machine-learning molecular dynamics can directly capture the kinetic selection of metastable phases in reactive materials systems.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.