Low thermal conductivity of the layered oxide ( N a , C a ) Co 2 O 4 : Another example of a phonon glass and an electron crystal

By K. Takahata, Y. Iguchi, D. Tanaka, T. Itoh, I. Terasaki. 2000

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The thermal conductivity of polycrystalline samples of $(\mathrm{N}\mathrm{a},\mathrm{C}\mathrm{a}){\mathrm{Co}}_{2}{\mathrm{O}}_{4}$ is found to be unusually low, 20 mW/cmK at 280 K. On the assumption of the Wiedemann-Franz law, the lattice thermal conductivity is estimated to be 18 mW/cm K at 280 K, and it does not change appreciably with the substitution of Ca for Na. A quantitative analysis has revealed that the phonon mean free path is comparable with the lattice parameters, where the point-defect scattering plays an important role. Electronically the same samples show a metallic conduction down to 4.2 K, which strongly suggests that ${\mathrm{NaCo}}_{2}{\mathrm{O}}_{4}$ exhibits a glasslike poor thermal conduction together with a metal-like good electrical conduction. The present study further suggests that a strongly correlated system with layered structure can act as a material of a phonon glass and an electron crystal.

Subfields: Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/98cec56dbdb247e1f2f6e1612a6fb24a7ee303db