Beyond complementarity: a reverse-engineering framework for de novo crystal structure determination from EXAFS.

This work introduces reverse EXAFS analysis (REA), a novel, ab initio framework that transforms extended X-ray absorption fine structure (EXAFS) spectroscopy from a complementary local probe into a primary tool for de novo crystal structure determination. By integrating iterative FEFF simulations with a reverse-fitting algorithm, REA directly extracts full crystallographic parameters, lattice constants, space group and atomic positions, from EXAFS oscillations, without requiring the user to supply an initial structural model from X-ray diffraction; instead, candidate models are retrieved from crystallographic databases and evaluated against EXAFS data. Validated on LiCrO2 and CuFeO2, REA uncovered unexpected phase complexities in CuFeO2, identifying secondary CuFe2O4 and CuFe5O8 phases undetected by conventional methods. This paradigm shift enables accurate structure solving in disordered, nanostructured and novel materials where diffraction fails, establishing EXAFS as a stand-alone crystallographic technique.