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arXiv · 1505.02635

Divacancy superstructures in thermoelectric calcium-doped sodium cobaltate

D. G. Porter·M. Roger·M. J. Gutmann·S. Uthayakumar·D. Prabhakaran·A. T. Boothroyd·M. S. Pandiyan·J. P. Goff
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Abstract

We have grown single crystals of Na$_x$Ca$_y$CoO$_2$ and determined their superstructures as a function of composition using neutron and x-ray diffraction. Inclusion of Ca$^{2+}$ stabilises a single superstructure across a wide range of temperatures and concentrations. The superstructure in the Na$^+$ layers is based on arrays of divacancy clusters with Ca$^{2+}$ ions occupying the central site, and it has an ideal concentration Na$_{4/7}$Ca$_{1/7}$CoO$_2$. Previous measurements of the thermoelectric properties on this system are discussed in light of this superstructure. Na$_{4/7}$Ca$_{1/7}$CoO$_2$ corresponds to the maximum in thermoelectric performance of this system.

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D. G. Porter, M. Roger, M. J. Gutmann, S. Uthayakumar, D. Prabhakaran, A. T. Boothroyd, M. S. Pandiyan, J. P. Goff. 2015-05-11. Divacancy superstructures in thermoelectric calcium-doped sodium cobaltate. https://doi.org/10.1103/physrevb.90.054101

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