NEW MANGANESE-SUBSTITUTED NICKEL HYDROXIDES .1. CRYSTAL-CHEMISTRY AND PHYSICAL CHARACTERIZATION

Substitution of over 20% of trivalent manganese for nickel leads to a-type nickel hydroxides. In these materials, prepared by precipitation, the compensation of the positive charge excess within the slab results from the insertion of CO32- anions in the interslab space, as previously reported in the homologous cobalt or iron systems. These phases are unstable in the 5 M KOH electrolytic medium. The evolution of the materials during ageing has been studied by X-ray diffraction, infrared spectroscopy and magnetic measurements. It appears clearly that a structure interstratification, related to the spontaneous oxidation of the Mn3+ to Mn4+ ions, occurs. The tetravalent state of these ions in the interstratified phases leads to assume the existence of proton deficiencies within the slab since the amount of CO32- inserted as charge compensating species is limited by steric effects.