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|Title:||Atomistic prediction of equilibrium vacancy concentrations in Ni3Al|
|Author:||Koning, Maurice de|
Miranda, Caetano R.
|Abstract:||We conduct a series of atomistic simulations to predict thermal equilibrium vacancy concentrations in ordered Ni3Al and compare the results to recent positron-annihilation spectroscopy experiments. Using a tight-binding second-moment-approximation potential to describe the atomic interactions, we compute single point-defect formation free energies as a function of temperature using both a quasiharmonic approximation (QHA) method and an ‘‘exact’’ technique based on nonequilibrium free-energy estimation (NFE), which includes all anharmonic effects. The corresponding thermal equilibrium concentrations are then computed by minimizing the crystal free energy with respect to the defect concentrations within the noninteracting-defect approximation, following the canonical ensemble approach of Hagen and Finnis [Philos. Mag. A 77, 447 (1998)]. It is found that the agreement between the NFE predictions for the effective formation enthalpies and entropies and experimental data is good for three near-stoichiometric compositions. The QHA results for the same compounds, however, deviate systematically and substantially from the experimental results, suggesting that the influence of anharmonicities on the formation thermodynamics of vacancies in ordered Ni3Al compounds is significant.|
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|Editor:||American Physical Society|
|Citation:||Physical Review B. American Physical Soc, v. 66, n. 10, 2002.|
|Appears in Collections:||IFGW - Artigos e Outros Documentos|
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