Hydrogen Solution in Tetrahedral Interstitial Sites in ZrCo Hydrides: A First-Principles Study

This work aims to investigate the characteristics of the H atom in the tetrahedral interstitial sites of 8f₂, 4c₁, 8f₁, 4c₂, 8e, and 8g₁ in the ZrCoH₃ cell by first principles calculation based on the density functional theory. The research shows that pressure can change the local property of the electrons and the bonding ability of the H atom and its adjacent metal atoms, resulting in changes in the stable point and the disproportion point of the H atom in ZrCoH₃. Further research has found that at P = 0 GPa, the significant Co-H covalent bond makes the H atom prefer to occupy the tetrahedral interstitial sites of 8f₁ and 4c₂ in the ZrCoH₃ cell, while the H atom occupying the tetrahedral interstitial site of 4c₁ in the ZrCoH₃ cell has a significant Zr-H ionic bond with its adjacent Zr atom, which is the reason for the disproportionation of the ZrCoH₃ alloy. When P = 10 GPa, the H atoms become unstable in the 8f₁ and 4c₂ tetrahedral interstices of the ZrCoH₃ crystal cell. The significant Zr-H ionic bond between the H atoms in the 8f₁ tetrahedral interstice and their adjacent Zr atoms is the reason for the disproportionation of the ZrCoH₃ alloy, and the significant Co-H covalent bond makes the H atoms preferentially occupy the 4c₁ and 8g₁ tetrahedral interstices.