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Effect of Na content and hydration on the excitation spectrum of the cobaltite Na_xCoO_2 yH_2O

P. Lemmens·V. Gnezdilov·N. N. Kovaleva·K. Y. Choi·H. Sakurai·E. Takayama-Muromachi·K. Takada·T. Sasaki·F. C. Chou·C. T. Lin·B. Keimer
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Abstract

We report on a Raman scattering study on the superconducting cobaltite $Na_xCoO_2\cdot yH_2O$ as function of Na content and hydration (x$\approx$1/3, 3/4 and y$\approx$0, 2/3, 4/3). The observed phonon scattering and scattering continua are analyzed in terms of lattice strain due to the structural misfit and disorder. Hydration, due to the intercalation of one or two $H_2O$ layers, releases a part of this strain. Our Raman data suggest a connection between disorder on the partly occupied Na sites, the split off of the $a_{1g}$ level from the other $t_{2g}$ states of $Co^{4+}$ and superconductivity.

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P. Lemmens, V. Gnezdilov, N. N. Kovaleva, K. Y. Choi, H. Sakurai, E. Takayama-Muromachi, K. Takada, T. Sasaki, F. C. Chou, C. T. Lin, B. Keimer. 2003-09-08. Effect of Na content and hydration on the excitation spectrum of the cobaltite Na_xCoO_2 yH_2O. https://doi.org/10.1088/0953-8984%2F16%2F11%2F041

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