Local structures around the substituted elements in mixed layered oxides

Abstract

The chemical substitution of a transition metal (M) is an effective method to improve the functionality of a material, such as its electrochemical, magnetic, and dielectric properties. The substitution, however, causes local lattice distortion because the difference in the ionic radius (r) modifies the local interatomic distances. Here, we systematically investigated the local structures in the pure (x = 0.0) and mixed (x = 0.05 or 0.1) layered oxides, Na(M1−xM′x)O2 (M and M′ are the majority and minority transition metals, respectively), by means of extended X-ray absorption fine structure (EXAFS) analysis. We found that the local interatomic distance (dM-O) around the minority element approaches that around the majority element to reduces the local lattice distortion. We further found that the valence of the minority Mn changes so that its ionic radius approaches that of the majority M.

Unveiling the Occurrence of Co(III) in NiCo Layered Electroactive Hydroxides: The Role of Distorted Environments

“…In addition, in order to correlate the DFT + Uc alculation with the experimental data, the intrinsicb ehavior of each constituent (oxidation state, average coordination number,i nteratomic distances and degree of disorder for each atom) must be assessed by an element-selective technique, such as X-ray absorption spectroscopy (XAS), with local atomic-order sensitivity. [42,43,44] In search of the chemical aspects that control the occurrence of Co(III) in NiCo layered hydroxides, we envisaged as ystematice xploration of nanotextured a-NiCo hydroxides, [45] obtained through the EpoxideR oute. [46] This one-pot room temperaturem ethod drives the precipitation under extremely mild conditions, offeringareliable tool to crystallize nanolayered hydroxides containing diverse cations [47] and/or interlamellar anions [48] The specimens were thoroughly characterizedb y PXRD,U V/Vis, SEM, and XANES-EXAFS, showing the dependence of Co(III) on the respective Ni content.M eanwhile, am icroscopicd escription, provided by DFT + Ud epictsa ne xtraordinary change on the electronic properties of the system, modulated by the incorporation of Ni atoms into the a-Co hydroxides upercell.…”

“…A microscopic understanding of the electronic structures and structural environments of Ni and Co ions inside the layers are necessary for a reliable in‐depth study of their physical and physicochemical properties. In addition, in order to correlate the DFT+U calculation with the experimental data, the intrinsic behavior of each constituent (oxidation state, average coordination number, interatomic distances and degree of disorder for each atom) must be assessed by an element‐selective technique, such as X‐ray absorption spectroscopy (XAS), with local atomic‐order sensitivity [42, 43, 44] …”

Aggregation tendency of guest Fe in NaCo1−xFexO2 (x < 0.1) as investigated by systematic EXAFS analysis

“…The background subtraction, normalization and analyses of EXAFS spectra were performed using the ATHENA program and EXAFS analyses were performed using the ARTEMIS programs 23 as described elsewhere 18,20 . First, the oscillatory components were extracted using the ATHENA program after background subtraction and normalization of the absorption spectra.…”

Invariant nature of substituted element in metal-hexacyanoferrate

“…The chemical substitution of transition metal ( M ) is an effective method to improve the functionality of materials, such as electrochemical performance in sodium-ion secondary batteries (SIBs) and critical temperature of magnetic phase transition. Actually, the rate and cycle properties of manganese hxacyanoferrate (Mn-HCF) in SIBs are significantly improved by partial substitution of Fe, Co, and Ni for Mn 1 – 3 . In addition, the critical temperature for the spin-crossover transition of [Fe 1- x Zn x (ptz) 6 ](BF 4 ) 2 decreases with the Zn concentration ( x ) 4 .…”

“…To minimize the Gibbs free energy, the local distortion should relax via variation in the electronic state of M g . Actually, in layered oxide system 1 , the M g valence changes so that local M g -O distance ( d M -O g ) approaches the M h -O distance ( d M -O h ).…”