The electronic structure of ε′-V2O5: an expanded band gap in a double-layered polymorph with increased interlayer separation

Abstract

Selective elimination of network connectivity has emerged as an effective means of modifying the electronic structure of materials. Given its unique properties and diversity of polymorphs, V₂O₅ is an outstanding candidate. Recent studies have highlighted the benefit of utilizing metastable materials as cathode materials for multivalent ion batteries. In particular, novel polymorphs accessible from topochemical modification of ternary vanadium oxide bronzes have been identified as particularly interesting intercalation hosts. This is a study of the electronic structure of one such polymorph, ε′-V₂O₅, using soft X-ray spectroscopy measurements and density functional theory calculations. This new double-layered polymorph of V₂O₅ has an increased interlayer separation that is found to lead to a dramatic increase in the band gap. Furthermore, the distortions brought on by the exfoliation process lead to a complex RIXS spectrum, showing d–d excitations, as well as low-energy charge transfer excitations. The comparison of the measurements and calculations is used to refine the crystal structure of ε′-V₂O₅, which cannot be directly determined from X-ray diffraction data. In addition, distinct aspects of the electronic structure that make such polymorphs useful for correlated electron devices and electrode materials for intercalation batteries are discussed and linked to the crystal structure.