Charge-ordering signatures in the optical properties of beta-Na0.33V2O5.
Temperature dependent optical spectra are reported for beta-Na0.33V2O5. The sodium ordering transition at T(Na)=240 K and, in particular, the charge ordering transition at T(MI)=136 K strongly influence the optical spectra. The metal-insulator transition at T(MI) leads to the opening of a pseudogap ( variant Planck's over 2pi omega=1700 cm(-1)) and to the appearance of a large number of optical phonons. These observations and the presence of a midinfrared band (typical for low dimensional metals) strongly suggest that the charge carriers in beta-Na0.33V2O5 are small polarons.
Presura
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Material Science Center, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Popinciuc
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van Loosdrecht
P H M
PH
van der Marel
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Mostovoy
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M
Yamauchi
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T
Ueda
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Y