Comment on “Raman spectroscopy study of NaxCoO2 and superconducting NaxCoO2∙yH2O”
P. Lemmens, P. Scheib, Y. Krockenberger, L. Alff, F. C. Chou, C. T. Lin, H.-U. Habermeier, B. Keimer
DOI 10.1103/PhysRevB.75.106501 · Physical Review B
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Abstract
The effect of surface degradation of the thermolectric cobaltite on Raman spectra is discussed and compared to experimental results from Co3O4 single crystals. We conclude that on NaCl-flux grown NaxCoO2 crystals a surface layer of Co3O4 easily forms that leads to the observation of an intense phonon around 700cm−1 [Y. G. Shi et al., Phys. Rev. B 70, 052502 (2004)]. The Raman spectra on freshly cleaved crystals from optical floating zone ovens do not show such effects and have a high-frequency phonon cutoff at approximately 600cm−1 [P. Lemmens et al., Phys. Rev. Lett. 96, 167204 (2006)]. We discuss the relation of structural dimensionality, electronic correlations, and the high-frequency phonon cutoff of the thermolectric cobaltite.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| NaxCoO2.yH2O Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | — | Pressure not reported | unknown |
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