Water-dependent structural and chemical relaxation of bulk Co3O4 from cobalt nitrate decomposition

The cell size of Co3O4 powders from exhaustively long cobalt nitrate decomposition (T = 260-850 degreesC) is shown to depend on heating temperature and to expand upon prolonged room temperature ageing (1 year). By means of TGA and gas mass analyses, water from the starting salt is bound to the product oxide to various extents and is spontaneously released over time. Excess non-stoichiometric oxygen is left unaffected. A relation is observed between expanding cell size and decreasing bound water, suggesting that water is dissociatively accommodated in the lattice. The result is not within current defectivity models for Co3O4.