Phase equilibria of the zinc oxide-cobalt oxide system were studied by a combination of X-ray diffraction and in situ electrical conductivity and thermopower measurements of bulk ceramic specimens up to 1000°C in air. Rietveld refinement of X-ray diffraction patterns demonstrated increasing solubility of Co in ZnO with increasing temperature, which is supported by the slight increase in wurtzite (Zn1-xCoxO) cell volume and lattice parameter a versus temperature determined for the phase boundary compositions. Similarly, the solubility of Zn in CoO increased with increasing temperature. In contrast, the spinel phase (ZnzCo3-zO 4) exhibited retrograde solubility for Zn. Electrical measurements showed that the eutectoid temperature for transformation of rocksalt Co 1-yZnyO into wurtzite and spinel is 894 ± 3°C, and the upper temperature limit of the stability of the spinel phase is 894°C-898°C for the compositions Co/(Zn+Co) = 0.82-1. The resulting composition-temperature phase diagram is presented and compared to the earlier (1955) diagram by Robin.
All Science Journal Classification (ASJC) codes
- Ceramics and Composites
- Materials Chemistry