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Hydrogen insertion in Ti2AlC and its influence on the crystal structure and bonds
Q. Liu, H. M. Ding, B. Q. Du, K. Y. Chu, Y. Shi
Abstract
First-principles calculations have been performed to study hydrogen insertion in Ti2AlC and its influence on the crystal structure and bonds. It has been found that H insertion in interstitial sites of the Ti-Al layers is thermally favorable and H diffusion along the basal plane is feasible. When H is inserted into tetrahedral interstitial sites (Itetr-2) surrounded by three Ti atoms and one Al atom, the surrounding Ti-Al bonds will be substituted by H-Al and H-Ti bonds. When H is inserted into hexagonal interstitial sites (Ihexa-5) surrounded by three Al and two Ti atoms, the Ti-Al bonds will be weakened while H-Ti bonds will be formed, at the same time, surrounding Al-Al bonds will be substituted by H-Al bonds, which will result in a change of part of the crystal structure of the Al layers. In comparison, H insertion into octahedral interstitial sites (Ioct-3) surrounded by three Ti and three Al atoms has the least influence on the Ti-Al bonds. As a result, H insertion into Itetr-2 will seriously weaken the bonding between the Ti and Al layers while H insertion into Ihexa-5 and Ioct-3 will enhance it. It is considered that the influence of H on the properties of Ti2AlC closely depends on its insertion position.
Keywords
MAX phases, Ti2AlC, first-principles calculations.
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