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 i onic configurations of these compounds have been established by associ ating powder neutron diffraction, thermogravimetric measurements and X PS 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 diffe rent cation fractions in both sites. The XPS spectroscopy analysis sho ws a predominately divalent copper, localized in tetrahedral sites. Th e monovalent copper is also present, but at a much smaller content. Th e additional information supplied by Mn2+ tetrahedral thermogravimetri c measurements resolves the cation distribution in these compounds. Fi nally; the discussion of the electrical properties using these structu ral formulas has shown that the presence of copper probably induces a mean-range hopping, the average distance of jumps being estimated to a pproximate to 9 Angstrom.