The influence of second-nearest neighbor interactions on the thermodynamic properties of B2 phases with substitutional defects |
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Authors: | Herbert Ipser Joachim P Neumann Prog Y Austin Chang |
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Institution: | (1) Materials Department, College of Engineering and Applied Science, University of Wisconsin, 53201 Milwaukee, WI, U.S.A.;(2) Present address: Karenz-Urlaub vom Institut für Anorganische Chemie der Universität Wien, Österreich |
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Abstract: | In order to explain some discrepancies between the theoretical predictions and the experimental data for the thermodynamic properties of substitutional B 2 phases,Chang's theoretical model is extended by including the influence of second-nearest neighbor interactions. For this purpose a new parameter is introduced which is defined as the ratio of the interchange energies between second-nearest and first-nearest neighbors. Theoretical equations are derived for the compositional dependence of the activity and the partial molar enthalpy. Using literature data, the following phases are re-evaluated in terms of the disorder parameter and the newly introduced parameter : -AuZn, -AuCd, -AgMg, and -NiZn. Very good agreement is found between the theoretical curves and the experimental data for the four systems. The values of obtained range from 0.0 for -NiZn to 0.5 for -AuZn. The inclusion of second-nearest neighbor interactions has little influence on the values of . It is shown that the behavior of the activity curve in -AuZn can be explained in a physically more meaningful way by including interactions between all second-nearest neighbors rather than interactions between gold substitutional defects only, as was done byLibowitz.With 5 Figures |
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