Optical properties of NaxV2O5

TL;DR

This study investigates the optical properties of sodium-deficient NaxV2O5 crystals across a broad energy spectrum, revealing their insulating nature, electronic gap features, and resonant Raman behavior linked to hole doping.

Contribution

It provides detailed experimental analysis of how sodium deficiency affects the optical and electronic properties of NaxV2O5, including gap development and resonance phenomena.

Findings

Insulating behavior persists up to 15% hole doping.

Optical absorption peak at 0.44 eV linked to impurity band formation.

Resonant Raman scattering observed at 2.8 eV due to hole doping.

Abstract

The optical properties of sodium-deficient NaxV2O5 (0.85 < x <1) single crystals are analyzed in the wide energy range, from 0.012 to 4.5 eV, using ellipsometry, infrared reflectivity, and Raman scattering techniques. The material remains insulating up to the maximal achieved hole concentration of about 15%. In sodium deficient samples the optical absorption peak associated to the fundamental electronic gap develops at about 0.44 eV. It corresponds to the transition between vanadium dxy and the impurity band, which forms in the middle of the pure NaV2O5 gap. Raman spectra measured with incident photon energy larger then 2 eV show strong resonant behavior, due to the presence of the hole-doping activated optical transitions, peaked at 2.8 eV.