Asymmetric effects in the extended X-ray absorption fine structure analysis of solid and liquid zinc

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Abstract
Extended X-ray absorption fine structure (EXAFS) results are presented for solid and liquid Zn for the temperature range 273 to 782 K. At the higher temperatures the distribution of nearest neighbour atoms is asymmetric. Neglect of the asymmetry and use of EXAFS analysis methods developed for symmetric distribution functions gives an underestimate of the nearest neighbour distance R1 and the disorder parameter σ12. It is shown that a transform analysis can be useful in detecting asymmetric effects, and methods of analyzing the EXAFS of asymmetric distributions are presented. An anharmonic oscillator model is applied to the EXAFS data of polycrystalline Zn to correct the values of R1 and σ12. The corrected values of σ12 are found to be~20% higher than those predicted by a Debye model. An empirical, analytically simple asymmetric distribution function is fitted to the liquid data to obtain promising agreement with the nearest neighbour structure as deduced from X-ray diffraction studies. Finally it is shown by applying the Blip-function model of liquid metals that, in principle, the large k-range spanned by EXAFS data can be used to specify the repulsive portion of the ion–ion interaction potential of liquid metals.

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