Study of NiO-CoO and Co3O4-Ni3O 4 Solid Solutions in Multiphase Ni-Co-O Systems

It is well-known that NiO-CoO solid solutions can easily be formed. However, the formation of Ni3O4-Co3O 4 solid solutions has not been recognized. In this article, it is reported that, whereas the calcination of a Ni(NO3)2 and Co(NO3)2 mixture with a 1:1 molar ratio at a high temperature above 800 °C generated a NiO-CoO solid solution, only a Ni 3O4-Co3O4 solid solution was observed after calcination at a low temperature of 500 °C. Furthermore, if the calcination was carried out in an intermediate temperature range from 600 to 700 ° both NiO-CoO and Ni3O4-Co3O 4 solid solutions could be formed. This occurred because Co 3O4 can induce the formation of Ni3O 4, whereas NiO can stabilize CoO. In addition, the lattice parameter of Ni3O4 was predicted using Vegards law to be 8.2054