Divacancy superstructures in thermoelectric calcium-doped sodium cobaltate

D. Porter (1) , M. Roger (2) , M. J. Gutmann (3) , S. Uthayakumar (1) , D. Prabhakaran (4) , A. T. Boothroyd (4) , M. S. Pandiyan (1) , J. P. Goff (1)

1 RHUL - Royal Holloway [University of London]
2 GMT - Groupe Modélisation et Théorie
3 ISIS - ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ISIS Neutron and Muon Source
4 Department of Physics, Clarendon Laboratory

We have grown single crystals of NaxCayCoO2 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 CoO2. Previous measurements of the thermoelectric properties on this system are discussed in light of this superstructure. Na 4/7 Ca 1/7 CoO2 corresponds to the maximum in thermoelectric performance of this system.

Domains: Physics [physics]

D. Porter, M. Roger, M. J. Gutmann, S. Uthayakumar, D. Prabhakaran, et al.. Divacancy superstructures in thermoelectric calcium-doped sodium cobaltate. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2014, 90, pp.054101. ⟨10.1103/PhysRevB.90.054101⟩. ⟨cea-01376304⟩