Synthesis of cobalt-aluminum spinels via EDTA chelating precursors

In this work, synthesis of nanocrystalline Co||Co||| x Al2−x O4 (where x = 0, 0.5, 0.8, 1, 1.18 and 2) spinels by the thermal decomposition of complex precursors derived from metal nitrate salts and ethylenediaminetetraacetic acid (EDTA) has been systematically studied. Based on XRD, FTIR, DTA, TGA, SEM and TEM analyses, it has been found that the as-prepared metal organic precursors with different Co and Al contents display different thermal behavior and crystal development and particle morphology. Increment of Co content in precursors improves the degree of crystallinity of the powder. Treated at 400°C, in contrast to the well formed Co3O4 or Co3O4-like spinel structure for the powder precursors containing higher Co content, most of the powders from precursors containing lower Co content are still amorphous. Higher Co content in the precursors slightly decreases the unit cell parameters of the resulting Co||Co||| x Al2−x O4 spinels. Prepared at 900°C, the unit cell parameters of Co||Al2O4, Co||Co||| 0.5Al1.5O4, Co||Co|||AlO4, Co||Co||| 2O4 are 8.1038, 8.1007, 8.0867, and 8.0834 A, respectively. Based on this work, preparation of a series of the Co||Co||| x Al2−x O4 spinels including black or bright blue Co||Al2O4, Co||Co||| 0.5Al1.5O4, Co||Co|||AlO4, Co||Co||| 2O4 from EDTA-Co(Al) complexing precursor has been established.