# Anisotropic Local Structure of SrFe2−xNixAs2 (x = 0.00, 0.16, and 0.23) Superconductor Probed by Polarized X-ray Absorption Fine Structure Measurements

## TL;DR

This study uses X-ray techniques to explore how nickel substitution affects the structure and electronic properties of a superconducting material.

## Contribution

The paper presents new insights into the anisotropic local structure and electronic states of SrFe2−xNixAs2 with varying Ni content.

## Key findings

- Ni substitution reduces bond lengths and displacements in the local structure.
- Valence electronic structure anisotropy decreases with increasing Ni content.
- The material's electronic structure becomes more isotropic as Ni is added.

## Abstract

We have investigated the effect of the Ni substitution on the local structure and the valence electronic states of the SrFe2−xNixAs2 (x = 0.00, 0.16, and 0.23) superconductor with a multi-edge extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopy. The As K-edge and Fe K-edge EXAFS measurements in the two polarizations (E‖ab and E‖c) show a clear change in the local structure with Ni concentration. The near-neighbor bondlengths and the related mean-square relative displacements (MSRDs) decrease as the Ni content increases. The polarized XANES spectra at the As, Fe and Ni K edges reveal a systematic change in the anisotropy of the valence electronic structure. The results suggest that the quasi 2D electronic structure of this system tends to become more isotropic as the Ni content increases. The local structure and the valence electronic states are discussed in the frame of the evolving electronic transport of the SrFe2−xNixAs2 system.