We have studied the local structure of Ca0.9Pr0.1Fe2As2, showing filamentary superconductivity above 40 K, by a combined analysis of Fe K-edge and As K-edge extended x-ray absorption fine structure measurements. The experiments are performed as a function of temperature exploiting a single crystal sample and in-plane polarization of the x-ray beam to extract information on the directional displacements. The local structure of the FeAs layer is found to be consistent with a regular FeAs4 tetrahedron containing negligible local disorder. Unlike other superconducting systems, we do not find any change in the atomic displacements across the superconducting transition temperature. The results are compatible with electron doping induced intrinsic superconductivity of optimized FeAs4 local structure containing negligible disorder.

We have studied the local structure of layered Eu(La,Ce)FBiS$_{2}$ compounds by Bi L$_3$ - edge extended x-ray absorption fine structure (EXAFS) measurements as a function of temperature. We find that...

Temperature-dependent Fe K-edge extended X-ray absorption fine structure (EXAFS) and Fe Kβ X-ray emission spectroscopy (XES) measurements are used to study the local structure and local Fe magnetic moment in the self-doped CaKFe 4 As 4 superconductor. The local Fe−As and Fe−Fe bond lengths show thermal expansion similar to the one found in other iron-based superconductors. The arsenic height from the Fe−Fe plane changes anomalously with a sharp decrease in the vicinity of the superconducting transition temperature. The Fe Kβ XES reveals that Fe in CaKFe 4 As 4 is in the low spin state, and the local magnetic moment decreases sharply while the sample is cooled across the transition temperature. The results indicate importance of the magnetoelastic coupling in the superconductivity with a key role of interlayer atomic correlations in these materials.

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The local structure of the filled tetragonal tungsten bronze (TTB) niobate Ba3Nb5−xTixO15 (x = 0, 0.1, 0.7, 1.0), showing a metal-insulator transition with Ti substitution, has been studied by Nb K-edge extended X-ray absorption fine structure (EXAFS) measurements as a function of temperature. The Ti substitution has been found to have a substantial effect on the local structure, that remains largely temperature independent in the studied temperature range of 80–400 K. The Nb-O bonds distribution shows an increased octahedral distortion induced by Ti substitution, while Nb-Ba distances are marginally affected. The Nb-O bonds are stiffer in the Ti substituted samples, which is revealed by the temperature dependent mean square relative displacements (MSRDs). Furthermore, there is an overall increase in the configurational disorder while the system with Nb 4d electrons turns insulating. The results underline a clear relationship between the local structure and the electronic transport properties suggesting that the metal-insulator transition and possible thermoelectric properties of TTB structured niobates can be tuned by disorder.