Synthesis, thermogravimetric and high temperature X-ray diffraction analyses of zinc-substituted nickel manganites

Abstract

Stoichiometric spinel phases Mn2.352xNi0.65ZnxO4 were prepared by thermal decomposition of mixed oxalate precursor powders Mn0.782aNi0.22ZnaC2O4znH2O (with 0 # a # 0.53) at 900°C. Cation-deficient phases Mn2.352xNi0.65Znxh3d/4O41d were identified in the temperature range 350–500°C. The nonstoichiometric coefficient d was found to strongly depend on the zinc content and the decomposition temperature. We showed that the introduction of zinc into the spinel phase enlarges the stability domain of the structure and inhibits oxidation at least up to 900°C. A cubic single-phase was observed for x # 1.00. The lattice parameter variation of the oxides in the composition range 0 # x # 0.60 can be explained using Poix’s method, in terms of the distribution of Zn21 cations on the tetrahedral sites. However, for higher zinc content (x . 0.6) a detailed analysis of data showed that a small fraction of Zn21 is located on octahedral sites.