Charge ordering signatures in the optical properties of beta-Na0.33V2O5

TL;DR

This study investigates how charge ordering and metal-insulator transitions in beta-Na0.33V2O5 affect its optical properties, revealing pseudogap formation, phonon emergence, and evidence for small polarons.

Contribution

It provides detailed temperature-dependent optical spectra showing charge and sodium ordering effects, and identifies small polarons as charge carriers in beta-Na0.33V2O5.

Findings

Charge ordering transition at 136 K influences optical spectra.

Metal-insulator transition leads to pseudogap opening.

Presence of mid-infrared band indicates small polarons.

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 \tmi leads to the opening of a psuedogap (\hbar\omega = 1700 cm-1), and to the appearance of a large number of optical phonons. These observations, and the presence of a mid-infrared band (typical for low dimensional metals) strongly suggests that the charge carriers in beta-Na0.33V2O5 are small polarons.