Year: 2003
Type: article
Abstract: We report measurements of room-temperature compressibility, thermal expansion, thermoelectric power \ensuremath{\alpha}(T) at various pressures $P<~20\mathrm{kbar},$ basal-plane resistivity ${\ensuremath{\rho}}_{\mathrm{ab}}(T),$ magnetic susceptibility, and thermal conductivity $\ensuremath{\kappa}(T)$ taken on single-crystal or cold-pressed ${\mathrm{Na}}_{1\ensuremath{-}x}{\mathrm{CoO}}_{2},$ $(1\ensuremath{-}x)\ensuremath{\approx}0.57.$ Whereas the c-axis thermal expansion is large, the basal-plane thermal expansion remains negligible for all temperatures $T<300\mathrm{K}.$ We propose here that pinning of the nominal Co(IV)/Co(III) redox couple at the top of the ${\mathrm{O}}^{2\ensuremath{-}}{:2p}^{6}$ bands, and a schematic location of the ${a}_{1}^{T}$ and ${e}^{T}$ antibonding bands of this couple with respect to the Fermi energy are responsible for the large thermoelectric power found in this compound. On the other hand, the phonon contribution to the thermal conductivity measured on a dense cold-pressed ceramic sample is not as small as previously reported.
Authors: F. Rivadulla, J.-S. Zhou, J. B. Goodenough
Institutions: Texas Materials Institute, The University of Texas at Austin
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W1618065068