Thermodynamics of impurity-enhanced vacancy formation in metals
Hydrogen induced vacancy formation in metals and metal alloys has been of great interest during the past couple of decades. The main reason for this phenomenon, often referred to as the superabundant vacancy formation, is the lowering of vacancy formation energy due to the trapping of hydrogen. By m...
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Veröffentlicht in: | Journal of applied physics 2017-01, Vol.121 (4) |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | Hydrogen induced vacancy formation in metals and metal alloys has been of great interest
during the past couple of decades. The main reason for this phenomenon, often referred to
as the superabundant vacancy formation, is the lowering of vacancy formation
energy due to
the trapping of hydrogen. By means of thermodynamics, we study the equilibrium
vacancy
formation in fcc metals (Pd, Ni, Co, and Fe) in correlation with the H amounts. The results of this
study are compared and found to be in good agreement with experiments. For the accurate
description of the total energy of the metal–hydrogen system, we take into account the binding
energies of each
trapped impurity, the vibrational entropy of defects, and the thermodynamics of divacancy formation. We
demonstrate the effect of vacancy formation energy, the hydrogen binding, and the divacancy binding
energy on the
total equilibrium vacancy concentration. We show that the divacancy fraction gives the
major contribution to the total vacancy fraction at high H fractions and cannot be neglected when
studying superabundant vacancies. Our results lead to a novel conclusion that at high hydrogen
fractions, superabundant vacancy formation takes place regardless of the binding energy between vacancies and hydrogen. We also
propose the reason of superabundant vacancy formation mainly in the fcc phase. The equations
obtained within this work can be used for any metal–impurity system, if the impurity
occupies an interstitial site in the lattice. |
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ISSN: | 0021-8979 1089-7550 |
DOI: | 10.1063/1.4974530 |