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Effects of lattice disorder in the UCu(5-x)Pd(x) system

Abstract

The UCu5-x Pdx system exhibits non-Fermi liquid (NFL) behavior in thermodynamic and transport properties at low temperatures for Pd concentrations 0.9 less than or approximately x less than or approximately 1.5. The local structure around the U, Cu, and Pd atoms has been measured for 0 less than or equal to x less than or equal to1.5 using the x-ray absorption fine structure (XAFS) technique in order to quantify the effects of lattice disorder on the NFL properties. A model which allows a percentage of the Pd atoms to occupy nominal Cu (16e) sites, s, was used to fit the Pd and Cu K edge and U LIII edge data. Pd/Cu site interchange was found to occur in all samples (x not equal to 0), reaching a minimum value of s similar to 0.17 at x = 0.7 and increasing monotonically to s similar or equal to 0.4 at x=1.5. These data also determine an upper limit on the static disorder of the nearest neighbor U-Cu pairs. A single-ion Kondo disorder model with a lattice-disorder origin of the distribution of f/conduction electron hybridization strengths within a tight-binding approach is used to calculate magnetic susceptibility. The results indicate that the measured U-Cu static disorder is not sufficient to explain the NFL behavior of the magnetic susceptibility within this variant of the Kondo disorder model, suggesting either that other sources of Kondo disorder exist or that the Kondo disorder model is not applicable to UCu5-x Pdx.

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