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

• Published in: Scientific reports Vol. 10; no. 1; p. 11283
• Main Authors: Moriya, Toshiaki, Niwa, Hideharu, Nitani, Hiroaki, Moritomo, Yutaka
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group 09.07.2020; Nature Publishing Group UK
• Subjects: Fourier transforms; Investigations; Iron; Materials science; Spatial distribution
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-020-68147-3

Abstract In transition metal ( M ) compounds, the partial substitution of the host transition metal ( M h ) to guest one ( M g ) is effective to improve the functionality. To microscopically comprehend the substitution effect, degree of distribution of M g is crucial. Here, we propose that a systematic EXAFS analysis against the M g concentration can reveal the spatial distribution of M g . We chose NaCo 1− x Fe x O 2 as a prototypical M compound and investigated the local intermetal distance around the guest Fe [ d Fe– M ( x )] against Fe concentration ( x ). d Fe– M ( x ) steeply increased with x , reflecting the larger ionic radius of high-spin Fe 3+ . The x -dependence of d Fe– M ( x ) was analyzed by an empirical equation, $${d}_{\mathrm{F}\mathrm{e}-M}(x)=sxd_{\mathrm{F}\mathrm{e}-\mathrm{F}\mathrm{e}}+(1-sx)d_{\mathrm{F}\mathrm{e}-\mathrm{C}\mathrm{o}}$$ d F e - M ( x ) = s x d F e - F e + ( 1 - s x ) d F e - C o , where d Fe–Fe and d Fe–Co are the Fe–Fe and Co–Fe distances, respectively. The parameter s represents degree of distribution of Fe; s  = 1, > 1, < 1 are for random, attractive, and repulsive distribution, respectively. The obtained s value (= 4.8) indicates aggregation tendency of guest Fe.