Structural insight into $C{o}_{3-x}M{n}_{x}Te{O}_6$; ($0<x\le 2$) solid solutions using Synchrotron X-ray diffraction and XANES

Abstract

Structural investigation on $C{o}_{3-x}M{n}_{x}Te{O}_6$; ($0<x\le 2$) solid solutions as a function of Mn concentration using Synchrotron X-ray diffraction (SXRD) and XANES measurements are presented. Phase diagram obtained from Rietveld Refinement on SXRD data as a function of Mn concentration indicates doping disproportionate mixing of both monoclinic (C2/c) and rhombohedral (R-3) structure (for $x<0.5$) while only R-3 symmetry for $x\ge 0.5$. Furthermore, Rietveld analysis on SXRD data shows increase in lattice parameters and average transition metal oxygen (Co/Mn-O) bond lengths for $x\ge 0.5$. Co and Mn K-edge XANES spectra reveal that both Co and Mn are in mixed oxidation state of $C{o}^{2+}/M{n}^{2+}$ and $C{o}^{3+}/M{n}^{3+}$. Relative ratio of $C{o}^{3+}/C{o}^{2+}$ and $M{n}^{3+}/M{n}^{2+}$ using Linear combination fit (LCF) decrease with increasing $x$ for $x\ge 0.5$. These structural and spectroscopic evidences are used to provide possible interpretation of the reported observations of maximum Neel Temperature (TN) at $x\sim 0.5$ and enhancements of antiferro/ferro-magnetic interactions in $C{o}_{3-x}M{n}_{x}Te{O}_6$ solid solutions.

26 pages including 10 figures and a table