Hydrogen trapping in MAX phase Ti3SiC2: 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.