Hydrogen trapping in MAX phase Ti₃SiC₂: Insight from chemical bonding by density functional theory

¹ Key Laboratory of Nuclear Physics and Ion- beam Application (MOE), Institute of Modern Physics, Fudan University - Shanghai 200433, China
² State Key Laboratory of Solid Lubrication, Lanzhou, Institute of Chemical Physics, Chinese Academy of Sciences - Lanzhou 730000, China
³ Department of Aeronautic and Astronautic, Fudan University - Shanghai 200433, China
⁴ Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics - Mianyang, 621900, China
⁵ School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology - Gardens Point Campus, QLD 4001, Brisbane, Australia

^(a) yxwang@fudan.edu.cn (corresponding author)

Received: 2 March 2017
Accepted: 12 June 2017

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.