Raman spectroscopy study of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="normal">Na</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:mi mathvariant="normal">Co</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>and superconducting<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="normal">Na</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:mi mathvariant="normal">Co</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>∙</mml:mo><mml:mi>y</mml:mi><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mi mathvariant="normal">O</mml:mi></mml:mrow></mml:math>

TL;DRAbstract

The Raman spectra of the parent compound ${\mathrm{Na}}_{x}\mathrm{Co}{\mathrm{O}}_{2}\phantom{\rule{0.2em}{0ex}}(x=0.75)$ and the superconducting oxyhydrates ${\mathrm{Na}}_{x}\mathrm{Co}{\mathrm{O}}_{2}∙y{\mathrm{H}}_{2}\mathrm{O}$ with different superconducting temperatures $({T}_{c})$ have been measured. Five Raman active phonons around $195\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ $({E}_{\mathit{1}g})$, $482\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, $522\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, $616\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ $(3{E}_{\mathit{2}g})$, and $663\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ $({A}_{\mathit{1}g})$ appear in all spectra. These spectra change systematically along with the intercalation of ${\mathrm{H}}_{2}\mathrm{O}$ and superconducting properties. In particular, the Raman active phonons (${A}_{\mathit{1}g}$ and ${E}_{\mathit{1}g}$) involving the oxygen mot

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