Cation distribution and mechanism of electrical conduction in nickel-copper manganite spinels

With the view of understanding the electrical conduction mechanism in the nickel-copper manganite spinels, the cation distribution and the ionic configurations of these compounds have been established by associating powder neutron diffraction, thermogravimetric measurements and XPS spectroscopy analysis. Neutron diffraction measurements allow us to reach the scattering lengths in both tetrahedral and octahedral sites. From this information we deduce lower and upper limits for the different cation fractions in both sites. The XPS spectroscopy analysis shows a predominately divalent copper, localized in tetrahedral sites. The monovalent copper is also present, but at a much smaller content. The additional information supplied by Mn2+ tetrahedral thermogravimetric measurements resolves the cation distribution in these compounds. Finally; the discussion of the electrical properties using these structural formulas has shown that the presence of copper probably induces a mean-range hopping, the average distance of jumps being estimated to approximate to 9 Angstrom.