Phase diagram, crystal chemistry and thermoelectric properties of compounds in the Ca-Co-Zn-O system |
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Authors: | W Wong-Ng T Luo WH Tang Q Huang S Chattopadhyay T Tritt |
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Institution: | a Ceramics Division, NIST, Gaithersburg, MD 20899, USA b NIST Center for Neutron Research, USA c Chemistry and Biochemistry Department, University of Maryland, MD 20745, USA d Physics Dept., Clemson University, Clemson, SC 29631, USA e Department of Physics, Zhejiang Sci-Tech University, Hangzhou 310018, China f BCPS Dept., Illinois Institute of Technology, Chicago, IL 60616, USA g Physics Department, Wuhan University, Wuhan 430070, China |
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Abstract: | In the Ca-Co-Zn-O system, we have determined the tie-line relationships and the thermoelectric properties, solid solution limits, and structures of two low-dimensional cobaltite series, Ca3(Co, Zn)4O9−z and Ca3(Co,Zn)2O6−z at 885 °C in air. In Ca3(Co,Zn)4O9−z, which has a misfit layered structure, Zn was found to substitute in the Co site to a limit of Ca3(Co3.8Zn0.2)O9−z. The compound Ca3(Co,Zn)2O6−z (n=1 member of the homologous series, Can+2(Co,Zn)n(Co,Zn)′O3n+3−z) consists of one-dimensional parallel (Co,Zn)2O66− chains that are built from successive alternating face-sharing (Co,Zn)O6 trigonal prisms and ‘n’ units of (Co,Zn)O6 octahedra along the hexagonal c-axis. Zn substitutes in the Co site of Ca3Co2O6 to a small amount of approximately Ca3(Co1.95Zn0.05)O6−z. In the ZnO-CoOz system, Zn substitutes in the tetrahedral Co site of Co3O4 to the maximum amount of (Co2.49Zn0.51)O4−z and Co substitutes in the Zn site of ZnO to (Zn0.94Co0.06)O. The crystal structures of (Co2.7Zn0.3)O4−z, (Zn0.94Co0.06)O, and Ca3(Co1.95 Zn0.05)O6−z are described. Despite the Ca3(Co, Zn)2O6−z series having reasonably high Seebeck coefficients and relatively low thermal conductivity, the electrical resistivity values of its members are too high to achieve high figure of merit, ZT. |
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Keywords: | Ca-Co-Zn-O phase equilibria Structure of Ca3(Co1 95Zn0 05)O6&minus z Structure of (Co2 7Zn0 3)O4&minus z Thermoelectric properties of Ca3(CoZn)4O9&minus z and Ca3(CoZn)2O6&minus z |
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