Electronic phase transitions of δ-Ag_xV₂O₅ nanowires: Interplay between geometric and electronic structures

Vanadium oxide bronzes, with the general formula M_xV₂O₅, provide a wealth of compositions and frameworks where strong electron correlation can be systematically (albeit thus far only empirically) tuned. In this work, we report the synthesis of single-crystalline δ-Ag_0.88V₂O₅ nanowires and unravel pronounced electronic phase transitions induced in response to temperature and applied electric field. Specifically, a pronounced semiconductor-semiconductor transition is evidenced for these materials at ca. 150 K upon heating, and a distinctive insulator-conductor transition is observed upon application of an in-plane voltage. An orbital-specific picture of the mechanistic basis of the phase transitions is proposed using a combination of density functional theory (DFT) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Structural refinements above and below the transition temperature, angle-resolved O K-edge NEXAFS spectra, and DFT calculations suggest that the electronic phase transitions in these 2D frameworks are mediated by a change in the overlap of d_xy orbitals.