Charge disproportionation and voltage-induced metal-insulator transitions evidenced in β-Pb_xV₂O₅ nanowires

The roster of materials exhibiting metal-insulator transitions with sharply discontinuous switching of electrical conductivity close to room temperature remains rather sparse, despite the fundamental interest in the electronic instabilities manifested in such materials and the plethora of potential technological applications ranging from frequency-agile metamaterials to electrochromic coatings and Mott field-effect transistors. Here, unprecedented, pronounced metal-insulator transitions induced by application of a voltage are demonstrated for nanowires of a vanadium oxide bronze with intercalated divalent cations, β-Pb_xV₂O₅ (x ≈ 0.33). The induction of the phase transition through application of an electric field at room temperature makes this system particularly attractive and viable for technological applications. A mechanistic basis for the phase transition is proposed based on charge disproportionation evidenced at room temperature in near-edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements, ab initio density functional theory calculations of the band structure, and electrical transport data, suggesting that transformation to the metallic state is induced by melting of specific charge localization and ordering motifs extant in these materials. A synthetic route to nanowires of β-Pb _xV₂O₅ and evidence of an unprecedented voltage-induced metal-insulator transition in these materials is presented. X-ray diffraction and X-ray absorption spectroscopy experiments are consistent with charge ordering and electronic structure calculations suggest the appearance of a mid-gap state.