Phase Equilibria of the Zinc Oxide–Cobalt Oxide System in Air

Abstract

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−zO4) exhibited retrograde solubility for Zn. Electrical measurements showed that the eutectoid temperature for transformation of rocksalt Co1−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.

Magnetic interactions in the Zn-Co-O system: tuning local structure, valence and carrier type from extremely Co doped ZnO to ZnCo2O4

“…Therefore, the preparation should be performed around this temperature in order to obtain the best possible results. For bulk crystals under ambient pressure it is known that a decomposition from Co 3 O 4 to CoO occurs at ~800 °C 23 24 25 . However, it is not unusual that off-equilibrium conditions like epitaxial growth on substrates in UHV may shift such types of decomposition in temperature.…”

A Molecular Approach to Self‐Supported Cobalt‐Substituted ZnO Materials as Remarkably Stable Electrocatalysts for Water Oxidation

“…We aimed at developing a rational bottom‐up approach towards intrinsically metastable Co:ZnO nanoparticles as precatalyst for effective (electro)chemical water oxidation. Although CoO dissolves readily in ZnO,16 high Co concentrations in ZnO demand refined synthetic approaches (including spray pyrolysis and MO‐CVD) 17. 18 As the solubility of CoO in ZnO changes from bulk to nanoscale and a high surface area is required for catalysis, the preparation of a nanocrystalline Co:ZnO material is imperative 19.…”

“…Although CoO dissolves readily in ZnO, [16] high Co concentrations in ZnO demand refined synthetic approaches (including spray pyrolysis and MO-CVD). Although CoO dissolves readily in ZnO, [16] high Co concentrations in ZnO demand refined synthetic approaches (including spray pyrolysis and MO-CVD).…”

Yolk-shelled ZnCo2O4 microspheres: Surface properties and gas sensing application

“…In this study, we build upon the successful use of binary metal oxides for sensing, now employing binary oxides made of cobalt and zinc. This choice was motivated by the high electronic conductivity and electrochemical activity of zinc cobalt oxide (ZnCo 2 O 4 ) used in Li-ion batteries [42] and as a hole transport layer in organic photovoltaics (PVs) [43]. Nanostructured ZnCo 2 O 4 in distinct shapes has been used to detect volatile organic compounds (VOCs) [29,30], such as methanol, formaldehyde, acetone and ethanol [22,34,44].…”