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Interstitial Chemistry of s-, p-, and d-Block Cations in Polymorphs of V2O5: An Atomistic and Electronic Structure Perspective
Abstract
Vanadium oxides are a versatile platform for examining the close coupling of spin, charge, orbital, lattice, and atomic degrees of freedom in electron-correlated materials. These compounds afford rich opportunities for precise tunability of electronic structure, phase instabilities, and for defining ionic and electronic conduction pathways. The intercalation of cations from across the periodic table within layered and tunnel-structured frameworks of vanadium oxides provides an opportunity to modulate electron correlation and engender electronic and structural transformations. Local ion dynamics and the coupling of ion motion with electron localization underpin a number of emerging technology applications, including the engineering of lone-pair states for photocatalysis, nonlinear dynamical transformations in brain-inspired electronic circuits, and manipulating cation diffusion pathways in cathodes for electrochemical energy storage. The versatility of intercalated ternary and quaternary vanadium oxides derive from the diverse range of structural distortions accessible in response to small variations in external fields such as temperature, pressure, strain, and chemical potential. Discontinuous structural and electronic transformations in these compounds are exquisitely sensitive to compositional modulation and can be tuned through the site-selective intercalation and positioning of ions of different sizes, polarizability, and stoichiometry within well-defined crystallographic sites.
In this dissertation, the removal and insertion of cations spanning the s-, p-, and d-block of the periodic table is effected for various stable and metastable phases of V2O5, in order to manipulate cation diffusion pathways for battery cathodes and perform electronic band-gap engineering in photocatalysts. By using topochemical methods to selectively remove or insert cations, kinetically trapping structures outside of thermodynamic equilibrium, compositional and structural variables can be isolated from each other and modulated with great precision. In particular, methods have been developed for accessing large single-crystals of a wide variety of vanadium oxide phases and performing macroscopic single-crystal-to-single-crystal transformations, removing and inserting guest cations while preserving the host lattice, in order to leverage single-crystal X-ray diffraction to acquire atomistic snapshots of structures in and out of equilibrium. The combination of topochemistry with single-crystal X-ray diffraction to image cation diffusion and lattice transformations in metastable materials has been successfully applied to structures with diverse host lattice architectures spanning tunnel-like and layered phases of V2O5. This approach has provided the first ever atomistic views of diffusion pathways in battery intercalation hosts, a longstanding challenge in the rational design of energy storage materials. Further, a palette of ternary, quaternary, and quintenary M^1x-(M^2y)(M^3z)V2O5 species has been developed, demonstrating the potential for multiple cations to be intercalated simultaneously with precise site selectivity and used as “chemical levers” in order to redirect cation traffic, modulate electronic structure, and stabilize high-energy interstitial sites in functional materials.
Citation
Handy, Joseph Viau (2022). Interstitial Chemistry of s-, p-, and d-Block Cations in Polymorphs of V2O5: An Atomistic and Electronic Structure Perspective. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /198523.