Hydrogen trapping in MAX phase Ti ₃ SiC ₂ : Insight from chemical bonding by density functional theory

Abstract

Understanding hydrogen (H) isotope trapping in materials is essential to optimize the material performance in a nuclear environment for the fabrication of nuclear devices. By using the density functional theory (DFT), herein we have systematically investigated the behaviour of hydrogen in the MAX phase Ti3SiC2 in the presence and absence of a vacancy (V). When a vacancy is generated in a favorable plane for hydrogen accumulating (Si plane), two distinct behavours of hydrogen in the Si plane have been identified by chemical bond analysis, i.e., the Ti-H and Si-H bonding, which synergistically results in VH2 complexes prevailing in the host matrix. Different from metals and other ceramics, the trapping mechanism of H in Ti3SiC2 essentially originates from the spatially inhomogeneous distribution of free-charge density and large discrepancy of electronegativity between the host atoms. Our theoretical results offer great insights into the rational design of new high-performance nuclear materials.

Parameters of the Unit Cell of the Ti3AlC2 MAX‐Phase with Hydrogen

“…These materials are resistant to oxidation and corrosion. [ 3 ] Applications of MAX phases as protective coatings stimulated both experimental [ 4–8 ] and theoretical [ 9–11 ] research of the properties of these materials with different point defects. It is shown experimentally that Ti 3 AlC 2 , Ti 2 AlC, Ti 3 SiC 2 , and Ti 2 AlN MAX phases are promising materials for the application in nuclear reactors because they have high high‐energy ion irradiation tolerance.…”

“…[ 9 ] The model of trapping the hydrogen by vacancies in the Ti 3 SiC 2 MAX phase was developed. [ 10 ] It was shown theoretically that the hydrogen atoms could more likely be incorporated into the Ti–Al layers in the Ti 3 AlC 2 MAX phase and diffusion of H in the Ti–Al layers was also feasible. [ 11 ] However, both theoretical calculations and experiments give an uncertain answer about the kinetics of hydrogen absorption and the amount of hydrogen in MAX phases.…”