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

Stoichiometric spinel phases Mn2.35-xNi0.65ZnxO4 were prepared by thermal decomposition of mixed oxalate precursor powders Mn0.78-alphaNi0.22ZnalphaC2O4. nH(2)O (with 0 less than or equal to alpha less than or equal to 0.53) at 900 degrees C. Cation-deficient phases Mn(2.35-x)Ni(0.65)Zn(x)square(3 delta/4)O(4+delta) were identified in the temperature range 350-500 degrees C, The nonstoichiometric coefficient delta 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 degrees C. A cubic single-phase was observed for x less than or equal to 1.00. The lattice parameter Variation of the oxides in the composition range 0 less than or equal to x less than or equal to 0.60 can be explained using Poix's method, in terms of the distribution of Zn2+ cations on the tetrahedral sites. However, for higher zinc content (x > 0.6) a detailed analysis of data showed that a small fraction of Zn2+ is located on octahedral sites. (C) 2000 Elsevier Science Ltd, All rights reserved.