Wang NL, Wu D, Li G, Chen XH, Wang CH, Luo XG. Infrared spectroscopy of the charge ordering transition of Na0.5CoO2.
PHYSICAL REVIEW LETTERS 2004;
93:147403. [PMID:
15524841 DOI:
10.1103/physrevlett.93.147403]
[Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2004] [Indexed: 05/24/2023]
Abstract
We report infrared reflectivity study of charge ordering in a Na0.5CoO2 single crystal. In comparison with x=0.7 and 0.85 compounds, we found that the effective carrier density increases systematically with decreasing Na contents. The charge ordering transition only affects the optical spectra below 1000 cm(-1). A hump near 800 cm(-1) develops below 100 K, which is accompanied by the appearance of new lattice modes as well as the strong antiresonance feature of phonon spectra. These observations signify a polaronic characteristic of charge carriers. Below T(co), an optical gap develops at the magnitude of 2Delta approximately 3.5k(B)T(co) (T<<T(co)), evidencing an insulating charge density wave ground state.
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