Multiple-edge EXAFS refinement: Short-range structure in liquid and crystalline Sn

L-edge extended x-ray-absorption fine structure (EXAFS) spectra of solid and liquid tin have been collected by using synchrotron radiation. Information on local structure has been obtained by simultaneous analysis of Sn L(3)-, L(2)-, and L(1)-edge EXAFS spectra by using an original data-analysis scheme based on the nb initio multiple-scattering GNXAS method. The use of the three edges allowed the extension of the energy range of the useful data increasing the accuracy of the derived structural parameters. Details of the multiple-edge data-analysis methodology are provided. The general interest of the method for multiple-edge structural studies of monatomic and multiatomic systems is discussed. A very good agreement with diffraction data is found for crystalline Sn. The first-neighbor distribution is studied as a function of temperature. Statistical errors on the structural parameters are provided. The model pair distribution function g(r) obtained by x-ray-diffraction data is refined in liquid Sn at T=245 degrees C. The EXAFS structural signal is shown to be very sensitive to the short-range correlations. The foot of the first peak of the g(r) is found to be steeper and the mean distance is found slightly shorter than previously indicated. Error bars on the g(r), due to random errors in the EXAFS data, are also shown. The signature of a three-body signal assigned to short-range covalent tetrahedral configurations is evidenced.