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In the present study, the local atomic structure of a Nb3Sn superconductor sample has been probed by X-ray absorption fine structure (XAFS) as a function of hydrostatic pressure (from ambient up to 26 GPa) using a diamond anvil cell set-up. The analysis of the Nb-K edge extended X-ray absorption fine structure (EXAFS) data was carried out combining standard multi shell structural refinement and reverse Monte Carlo method to provide detailed in situ characterization of the pressure-induced evolution of the Nb local structure in Nb3Sn. The results highlight a complex evolution of Nb chains at the local atomic scale, with a peculiar correlated displacement of Nb–Nb and Nb–Nb–Nb configurations. Such a local effect appears related to anomalies evidenced by X-ray diffraction in other superconductors belonging to the same A15 crystallographic structure. [ABSTRACT FROM AUTHOR]

Considering the proposed structural anomaly in the "topotactically" reduced compound CaMnO 2 , we investigated its local structure through extended x-ray absorption fine structure (EXAFS) spectroscopy. The in-depth analysis of the EXAFS results unraveled an unforeseen local chemical order of Mn and Ca, which helps to advance the previous understanding of average disordered scenario, obtained based on diffraction probes like x-ray and neutron. We established the microscopic origin of such locally ordered structure on the basis of Mn-O covalency through analysis of density functional theory calculations. Further, fluorination is attempted to explore the influence of modification of the anionic network and bond covalency. We found that the more ionic Mn-F bonds, compared to Mn-O bonds, drive a local phase separation between Mn-rich phase and Ca-rich phase. • CaMnO2: a member of CaMnO3- family (δ = 1) with Mn2+ ions residing within a rock-salt structure. • Studying the topotactic transformation and the local chemical order using EXAFS. • Indication of unusual local Ca/Mn order. • Stability of local structure explained on the basis of Mn-O covalency through DFT analysis. • Modification of the anionic network via fluorination driving a local phase separation in CaMnO2. [ABSTRACT FROM AUTHOR]

We have investigated magnetic, structural and dielectric properties of Bi 5 FeTi 3 O 15 (BFTO) in the temperature range 5K-300 K. Using diffraction, Raman spectroscopy and x-ray absorption fine structure measurements, iso-structural modifications are observed at low temperatures (≈100 K). The analysis of dielectric constant data revealed signatures of dielectric relaxation, concomitant with these structural modifications in BFTO at the same temperatures. Further, employing complementary experimental methods, it is shown that the distribution of Fe/Ti ions in BFTO is random. With the help of techniques that probe magnetism at various length and time scales, it is shown that the phase-pure BFTO is non-magnetic down to the lowest temperatures., (© 2021 IOP Publishing Ltd.)

The present work is aimed at exploring the local atomic structure modifications related to the spin reorientation transition (SRT) in DyFeO 3 orthoferrite exploiting x-ray absorption fine structure (XAFS) spectroscopy. For this purpose we studied by XAFS the evolution of the local atomic structure around Fe and Dy as function of temperature (10-300 K) in a DyFeO 3 sample having the SRT around 50-100 K. For sake of comparison we studied a YFeO 3 sample having no SRT. The analysis of the extended region has revealed an anomalous trend of Fe-O nearest neighbour distribution in DFO revealing (i) a weak but significant compression with increasing temperature above the SRT and (ii) a peculiar behavior of mean square relative displacement (MSRD) [[Formula: see text]] of Fe-O bonds showing an additional static contribution in the low temperature region, below the SRT. These effects are absent in the YFO sample supporting these anomalies related to the SRT. Interestingly the analysis of Dy L 3 -edge data also reveal anomalies in the Dy-O neighbour distribution associated to the SRT, pointing out a role of magnetic Re ions across [Formula: see text]. These results point out micro-structural modification at both Fe and Dy sites associated to the magnetic transitions in DFO, it can be stated in general terms that such local distortions across [Formula: see text] and magnetic Re 3+ may be present in other orthoferrites exhibiting multiferroic nature.