title: Charge-ordering signatures in the optical properties of beta-Na0.33V2O5.
abstract: 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.
authors.affiliation: Material Science Center, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
authors.forename: C
authors.initials: C
authors.lastname: Presura
authors.forename: M
authors.initials: M
authors.lastname: Popinciuc
authors.forename: P H M
authors.initials: PH
authors.lastname: van Loosdrecht
authors.forename: D
authors.initials: D
authors.lastname: van der Marel
authors.forename: M
authors.initials: M
authors.lastname: Mostovoy
authors.forename: T
authors.initials: T
authors.lastname: Yamauchi
authors.forename: Y
authors.initials: Y
authors.lastname: Ueda