In situ site-selective transition metal K-edge XAS: a powerful probe of the transformation of mixed-valence compounds

Abstract

We present herein the first in situ site-selective XAS experiment performed on a proof-of-principle transformation of a mixed-valence compound: the calcination of the K0.1Co(II)4[Co(III)(CN)6]2.7·20H2O Prussian Blue analogue (containing Co(2+) and Co(3+) ions in two different Oh sites) into Co3O4 (containing Co(2+) ions in a Td site and Co(3+) in an Oh site). By recording the Co K-edge X-ray absorption spectra using a spectrometer aligned at the Co Kβ1,3 emission line, the evolution of each species was singly monitored from 20 °C up to the oxide formation. The experimental spectrum of the Co(2+)(Td) and Co(3+) (Oh) species in Co3O4 is reported for the first time. Our results demonstrate the possibilities offered by site-selective XAS for the investigation of chemical transformations and the study of materials under working conditions whenever the chemical element of interest is present in several states and/or sites.

High‐Energy Resolution Fluorescence Detected X‐Ray Absorption Spectroscopy: A Powerful New Structural Tool in Environmental Biogeochemistry Sciences

“…Principle of X‐ray absorption spectroscopy (XAS)‐fluorescence measurement using solid‐state detector (SSD) and crystal analyzer spectrometer (CAS). Spectra correspond to the analysis of a Co 3 O 4 sample with a 30‐element Ge SSD (total fluorescence yield, red spectra) and a CAS using five Ge(444) crystals optimized around the Co K β 1,3 fluorescence line (high‐energy resolution fluorescence detected [HERFD], blue spectra; Bordage et al, 2015). (a) XAS spectra.…”

“…Depending on the selected transitions, XES is divided into two main regions: core‐to‐core (e.g., K α1,2 or K β1,3 ) and valence‐to‐core (e.g., K β2,5 ). In the example of K emission lines of 3d transition metals, core‐to‐core XES permits the evolution of the local spin or oxidation state to be followed and may be used in turn to collect oxidation state‐selective EXAFS (Glatzel et al, 2002) or XANES (Bordage et al, 2015). In addition, valence‐to‐core XES is more sensitive to metal‐ligand mixed valence states and has been employed in chemistry to distinguish between ligands of light elements (Eeckhout et al, 2009).…”

Temperature dependence of X-ray absorption and nuclear magnetic resonance spectra: probing quantum vibrations of light elements in oxides

“…Red triangles represent the cation in tetrahedral environments, the full and empty symbols correspond to the QHA and TEO (thermal expansion only) calculations, respectively. The dashed lines are the best fits using eqn (11). Saturation temperatures, T s , are given in ESI.…”

“…[3][4][5] Moreover, recent breakthroughs in methodology and instrumentation provide a qualitative enhancement of experimental data. [6][7][8][9][10][11] However, the use of accurate and appropriate theoretical tools is mandatory to fully interpret experiments. [12][13][14][15][16] Most state-of-the-art simulation methods neglect nuclear degrees of freedom by assuming that atoms are fixed at their equilibrium positions.…”

Breakdown of the Small‐Polaron Hopping Model in Higher‐Order Spinels

“…To extract the cation site-occupation, we employ the K β XES because of its sensitivity to the oxidation state, spin state, and ligand geometry of the cations. [12,23,24] We have shown that XES is more accurate than conventional techniques such as X-ray absorption spectroscopy. [12,19] The site-occupation of Mn x Fe 3−x O 4 can be summarized as x O 4 films have partially inverse spinel structure, where the degree of inversion "i" is defined as the fraction of M 3+ cations at T d sites (where M = Fe, Mn).…”