Comparative analysis of XANES and EXAFS for local structural characterization of disordered metal oxides. (10th August 2021)

• Record Type: Journal Article
• Authors: Li, Junying; Li, Yuanyuan; Routh, Prahlad K.; Makagon, Evgeniy; Lubomirsky, Igor; Frenkel, Anatoly I.
• Is Part Of: Journal of synchrotron radiation. Volume 28:Part 5(2021)
• Page Start: 1511
• Page End: 1517
• Publication Date: 2021-08-10
• Subjects: functional materials -- XAFS -- pre‐edge analysis -- local symmetry; Synchrotron radiation -- Periodicals; Free electron lasers -- Periodicals; 539.73505
• DOI: 10.1107/S1600577521007025
• Languages: English
• ISSNs: 0909-0495

Abstract

Abstract : This article evaluates the utility of pre‐edge analysis of X‐ray absorption near‐edge structure spectra for studying materials with variable amounts of disorder using two examples: a unimodal distribution of nearest neighbors of homogeneously distributed metal centers (Ti in Ti oxide nanocomposites) and a bimodal distribution due to the local structural heterogeneities around V in V oxide nanocomposites. In the latter case, both the pre‐edge analysis and conventional EXAFS analysis are combined to detect the presence of local structural heterogeneities. Abstract : In functional materials, the local environment around active species that may contain just a few nearest‐neighboring atomic shells often changes in response to external conditions. Strong disorder in the local environment poses a challenge to commonly used extended X‐ray absorption fine structure (EXAFS) analysis. Furthermore, the dilute concentrations of absorbing atoms, small sample size and the constraints of the experimental setup often limit the utility of EXAFS for structural analysis. X‐ray absorption near‐edge structure (XANES) has been established as a good alternative method to provide local electronic and geometric information of materials. The pre‐edge region in the XANES spectra of metal compounds is a useful but relatively under‐utilized resource of information of the chemical composition and structural disorder in nano‐materials. This study explores two examples of materials in which the transition metal environment is either relatively symmetric or strongly asymmetric. In the former case, EXAFS results agree with those obtained from the pre‐edge XANES analysis, whereas in the latter case they are in a seeming contradiction. The two observations are reconciled by revisiting the limitations of EXAFS in the case of a strong, asymmetric bond length disorder, expected for mixed‐valence oxides, and emphasize the utility of the pre‐edge XANES analysis for detecting local heterogeneities in structural and compositional motifs.