Kenneth Dorazio
Advisor: Prof. Faisal Alamgir

will defend a master’s thesis entitled,

Cobalt and Iron Core-Hole Spectroscopy: Experiment and Theory across Molecular and Periodic Systems

On

Thursday, November 19 at 10:30 a.m.
Molecular Science and Engineering Room 1222

or

 Virtually via MS Teams:

Meeting ID: 216 944 087 679 536
Passcode: nj7mK7id

Committee
            Prof. Faisal Alamgir – School of Materials Science and Engineering (advisor)
            Prof. Guoxiang (Emma) Hu – School of Materials Science and Engineering
            Prof. Henry La Pierre – School of Chemistry and Biochemistry
                       

Abstract

The electronic state of a cobalt or iron center — its oxidation state, spin state, coordination geometry and the covalency of its bonds — governs the function of battery cathodes, catalysts and metalloenzymes, and must be read element-specifically in the bulk. Core-hole spectroscopies read it: K-edge X-ray absorption (XAS) through the pre-edge and edge, Kα and Kβ X-ray emission (XES) through the exchange-split mainlines and the ligand-derived valence-to-core (VtC) lines, and resonant inelastic X-ray scattering (RIXS) through two-dimensional planes that separate what the one-dimensional spectra superimpose. This thesis builds a laboratory XES reference library for cobalt and iron and tests two families of first-principles calculation against it and against synchrotron XAS and RIXS.

The cobalt library — Kα, Kβ mainline and VtC spectra of 27 compounds spanning Co(II) and Co(III), high and low spin, octahedral and tetrahedral coordination, molecules and extended solids, all measured on one laboratory spectrometer — shows that the Kβ₁,₃–Kβ′ exchange splitting and the Kα₁ FWHM separate the spin manifolds, that the mainline descriptors are mutually linear across molecular and extended solids, and that three independent observables can be calibrated against DFT covalencies and read off for the extended solids. An iron Kβ library reproduces the same systematics for Fe(II) and Fe(III). For the extended solids, core-hole Bethe–Salpeter calculations (Quantum ESPRESSO/OCEAN) give site-resolved K-edge XANES, VtC emission, O K-edge and metal K-edge RIXS. Isolating coordination geometry in cobalt and iron oxides and iron phosphates shows that the tetrahedral pre-edge enhancement is reproduced quantitatively and assigned to the dipole intensity of the non-centrosymmetric site.  The same calculations are then carried across delithiation. For pristine and delithiated LiCoO₂ and LiFePO₄, the simulated RIXS planes agree well with the measured ones, and the projected densities of states support the assignment of the features. A final chapter turns to LiCoPO₄, where the involvement of oxygen and phosphorus in the redox chemistry is explored through O K-edge and P Kβ calculations in combination with preliminary experimental results and future directions.