ZnCo₂O₄ ceramics with a spinel-like structure are versatile functional materials which depending on the synthesis conditions may exhibit magnetic, electric, optical and/or catalytic characteristics. However under air atmosphere, cobalt ions experiment different red-ox processes with temperature, so contrary to many other spinel oxides, a low thermal stability can be expected for this cobaltite spinels. In addition, the final outcome of these transformations will be as well defined by the solid state chemistry of the ZnO–Co_xO_y couple, i.e. by the partial solubility of cobalt in zinc oxide and zinc in the different cobalt oxides. At first the similarity in charge and ionic size suggests the possibility of substitutional solid solution for both the Co^II into the ZnO wurtzite structure and the Zn^II into the CoO rock-salt structure. However it has been observed that once the spinel structure collapses, all the zinc diffuses into the rock salt phase.