Electronic Structure of β‑Na x V2O5 (x ≈ 0.33) Polycrystalline Films: Growth, Spectroscopy, and Theory

• Published in: Journal of physical chemistry. C Vol. 118; no. 2; pp. 1081 - 1094
• Main Authors: Chen, Bo, Laverock, Jude, Newby, Dave, Su, Ting-Yi, Smith, Kevin E, Wu, Wei, Doerrer, Linda H, Quackenbush, Nicholas F, Sallis, Shawn, Piper, Louis F. J, Fischer, Daniel A, Woicik, Joseph C
• Format: Journal Article
• Language: English
• Published: American Chemical Society 16-01-2014
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp410277m

We present a detailed study of the microstructure and electronic structure of β-Na x V2O5 (x ≈ 0.33) polycrystalline films, combining film growth, X-ray spectroscopies, and first-principles calculations. High-quality crystalline and stoichiometric V2O5 and β-Na0.33V2O5 films were grown by a sol–gel process, spin-coating, and rapid thermal annealing. The V2O5 film, which exhibits a rough surface, is preferentially oriented in the (001) direction perpendicular to the surface, whereas the b-axis of β-Na0.33V2O5 is oriented in the substrate plane. The β-Na0.33V2O5 film consists of a nested layered structure composed of single-crystalline rods of a few hundred nanometers in diameter and a few micrometers in length. Photoemission and X-ray absorption measurements of β-Na0.33V2O5 confirm the Na incorporation and the presence of mixed V5+ and V4+ species and weakly occupied V 3d states. At the V L-edge, X-ray absorption and resonant inelastic X-ray measurements suggest a larger crystal field for β-Na0.33V2O5 compared with isoelectronic β-Sr0.17V2O5. We observe the lowest local crystal-field dd* transition at an energy of ∼−1.6 ± 0.1 eV for β-Na0.33V2O5, which is substantially larger than β-Sr0.17V2O5; this large difference is interpreted as arising from the stronger distortions to the VO6 octahedra in β-Na0.33V2O5.