Local atomic structure of solid solutions with overlapping shells by EXAFS: The regularization method

Abstract The regularization method of solving ill-posed problem is used to determine five partial interatomic distances on the basis of combined two EXAFS spectra. Mathematical algorithm and experimental results of the EXAFS analysis for Ni c Zn 1− c O ( c  = 0.0, 0.3, 0.5, 0.7, 1.0) solid solutions with the rock salt (rs) crystal structure are discussed. Samples were synthesized from the binary oxide powders at pressure of 7.7 GPa and temperatures 1450–1650 K. The measurements were performed using synchrotron facilities (Russian Research Centre “Kurchatov Institute”, Moscow). The Ni and Zn K absorption spectra were recorded in transmission mode under room temperature. It is shown, the ideal rock salt lattice is distorted and long-range order exists only in the average (Vegard law). In order to determine coordinates ions for the solid solution with rock salt structure, we used the Pauling model. The simulation is performed for 343,000 cluster of oxide ions. The distribution functions for ions (Ni O, Ni Ni, Ni Zn, Zn Zn, Zn O, O O) depending on the distance are obtained. The width of the Gaussian distribution function is determined by the difference of the radii of the metal ions. The results are consistent with the data both X-ray diffraction and the EXAFS spectroscopy.