Sol–gel preparation of M-Sb oxides from Sb (OBun)3-M-acetate precursors with M = Mn, Co, Ni

Abstract

The sol–gel preparation of homogeneous oxide mixtures in the systems Mn–Sb–O, Co–Sb–O, Ni–Sb–O and Mn–Co–Ni–Sb–O has been investigated. The gel preparation using M(OAc)₂·4H₂O (M = Mn, Co and Ni) and Sb(OBuⁿ)₃ as precursors with diethylamine as additive and methanol as solvent is described. In these pseudobinary systems gels with M : Sb ratios ranging from 4:1 to 1:4 have been prepared. The thermal decomposition of these gels to yield oxide mixtures has been studied both in air and in nitrogen by TG and DTA. The gels and the oxide mixtures formed by heat treatment at 370 and 800°C have been studied with respect to homogeneity, morphology and occurrence of crystalline phases, by scanning electron microscopyenergy dispersive spectrometry (SEM–EDS) and X-ray powder diffraction. In general, homogeneous, X-rayamorphous oxide mixtures were formed by heating the gels in air to 370°C. At 800°C, MSb₂O₆ was formed in the pseudobinary systems together with Sb₂O₄ for Sb-rich mixtures, and M-oxides for M-rich ones. The two pseudoquarternary systems studied were almost X-ray amorphous after heat treatment at 800°C.