Role of Lattice Softening in Hydrogen-Induced Amorphization

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  • 水素誘起アモルファス化における格子ソフト化の役割
  • スイソ ユウキ アモルファスカ ニ オケル コウシ ソフトカ ノ ヤクワリ

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The atomistic mechanism of Hydrogen-Induced Amorphization (HIA) of AB2 C15 Laves phase compounds was investigated via constant-pressure molecular dynamics (MD) method using empirical Lennard-Jones interatomic potentials. Present simulations have successfully reproduced the experimental results that the CeNi2 compound shows HIA while the YAl2 compound does not show it. Our results show the softening effect due to the incorporation of hydrogen in both systems; the non-linearity of the interatomic potential leads to the softening effect via volume expansion. In addition, the CeNi2 compound shows more softening effect due to the relaxations of atomic positions of Cerium and Nickel atoms, while the YAl2 compound does not show it. We suggest that the key to induce HIA is whether A and B atoms can relax simultaneously by releasing the contraction of A and the expansion of B in Laves phase as the CeNi2 compound is the case. Such relaxations give the reduction of bulk modulus, and may be an indication of the elastic lattice instability. The obtained amorphous structure is a potentially favorable one, and HIA causes the potential-energy decrease, indicating the driving force is the potential-energy decrease. In contrast, solid-liquid melting causes the potential-energy increase, indicating the driving force is the entropic effect.

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