Divacancy superstructures in thermoelectric calcium-doped sodium cobaltate

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.

arXiv commentProduced using Revtex 4.1 and pdflatex. 7 Pages, 6 figures

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Cited by in corpus (2)

• Restoration of long range order of Na ions in $N{a}_{x}Co{O}_2$ at high temperatures by sodium site doping
• Dopant incorporation site in sodium cobaltate's host lattice: A critical factor for thermoelectric performance