Valence-to-core X-ray emission spectroscopy of vanadium oxide and lithiated vanadyl phosphate materials. Issue 32 (28th July 2020)

• Record Type: Journal Article
• Authors: Jahrman, Evan P.; Holden, William M.; Govind, Niranjan; Kas, Joshua J.; Rana, Jatinkumar; Piper, Louis F. J.; Siu, Carrie; Whittingham, M. Stanley; Fister, Timothy T.; Seidler, Gerald T.
• Is Part Of: Journal of materials chemistry. Volume 8:Issue 32(2020)
• Page Start: 16332
• Page End: 16344
• Publication Date: 2020-07-28
• Subjects: Materials -- Research -- Periodicals; Chemistry, Analytic -- Periodicals; Environmental sciences -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d0ta03620j
• Languages: English
• ISSNs: 2050-7488

Abstract

Abstract : Coupling lab-based XES measurements with computations amenable to solid-state systems revealed the valence band behavior of several vanadium-based electronic materials. Abstract : We report valence-to-core (VTC) X-ray emission spectroscopy (XES) measurements and theoretical calculations of the electrochemical sequence ε-VOPO4, ε-LiVOPO4, ε-Li2 VOPO4 and the reference oxides V2 O3, VO2, and V2 O5 . In our analysis of these results, we establish a framework for interrogating chemical bonding that is generally applicable to a wide range of systems, including complex, extended inorganic compounds. While this latter regime has garnered less focused application than, e.g., metalloenzymes in many excellent catalysis studies, we show that the technique provides high utility in materials-focused energy storage research. Here, sensitivities to the local atomic structure and hybridization schemes are discussed in detail. Similarly, the effect of lithiation on oxidation, delocalization, and shifts in ligand valence energy levels are all readily apparent in the analyzed results. Finally, the TDDFT projections clearly reveal the directional dependencies of the valence band at each of the vanadium sites. Our results demonstrate laboratory-based X-ray spectroscopy instrumentation is a viable route for attaining well-resolved VTC-XES features for inorganic compounds of 3d transition metals, even for samples of limited quantity or suffering from sensitivity to the atmosphere. The experimental results are in good agreement with results produced by real-space Green's function and time-dependent density functional theory (TDDFT) methods, respectively. Hence, we propose that VTC-XES, when equipped with appropriate theoretical support, can be a valuable complement to X-ray absorption pre-edge features for more detailed characterization of a compound's electronic structure. We expect similar analyses will find application in a broad range of materials chemistry research and provide both fundamental and applied insights.