Correlation between band structure and hydride formation in dilute palladium alloys |
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Authors: | RV Bucur D Lupu |
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Institution: | Institute of Isotopic and Molecular Technology, P.O. Box 243, R-3400 Cluj-Napoca, Romania |
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Abstract: | Data on the free energy change ΔG, following solution of hydrogen in dilute Pd-alloys Pd1?xMx have been reviewed for different concentrations of M (M = Au, Ag, Pt, Ir, Rh, V, Cu, Ni, Pb, Sn and Ti) in both the α and β phases. The dependence of ΔG values upon the nature of the substituents (transition metals) is consistently explained within the framework of a metal-hydrogen bonding mechanism in the hydrides. For the β-hydride the ΔG values can be calculated on the basis of the equation ΔG = ΔGpd + a(T)(〈?MLB〉 ? 〈?PdLB〉)x, where atom and is the free energy change of solution of hydrogen in pure Pd, a(T) = 0.194 at T = 298 K, 〈?mLB〉 and 〈?pdLB〉 are the average energies of the lowest band of the pure constituents (). The stability of the palladium-hydrogen bond in dilute Pd-alloys depends on the value of 〈?MLB〉; for substituents having lower 〈?MLB〉 values than Pd the bond will strengthen, while for those having higher 〈?MLB〉 values it will weaken. This behaviour agrees well with the general trend of the stability of the stoichiometric hydrides predicted by Gelatt, Ehrenreich and Weiss using band structure results. |
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