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

Authors

  • Nicola H. Perry,

    1. Department of Materials Science & Engineering, Northwestern University, Evanston, Illinois
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    • Member, The American Ceramic Society.
  • Thomas O. Mason

    Corresponding author
    • Department of Materials Science & Engineering, Northwestern University, Evanston, Illinois
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    • Fellow, The American Ceramic Society.

Author to whom correspondence should be addressed. e-mail: t-mason@northwestern.edu

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.

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