Comparison of the local structures of Ca0.82La0.18FeAs2 and Ba0.64K0.36Fe2As2 pnictide superconductors using atomic pair distribution function analysis

• Atomic pair distribution function (atomic PDF) of the Ca0.82La0.18FeAs2 pnictide superconductor is presented.
• The atomic PDF functions of the Ca0.82La0.18FeAs2 and Ba0.64K0.36Fe2As2 are compared.
• Both Ba0.64K0.36Fe2As2 and Ca0.82La0.18FeAs2 sustain relative large local disorder in the Fe-Fe network.
• Nanoscopic manipulation of the active layer is the key to modulate the electronic properties of iron-based superconductors.

A comparative local structure study of pnictide superconductors Ca0.82La0.18FeAs2 (112-type, Tc∼ 40 K) and Ba0.64K0.36Fe2As2 (122-type, Tc∼ 37 K), using room temperature x-ray total scattering measurements is reported. The Fe–As superconducting active layer is found to be globally similar in both the systems consisting of edge-sharing FeAs4/4 tetrahedra as in all the iron-pnictide superconductors discovered so far. Although optimally superconducting, the active layer in these compounds is found to sustain a large local inhomogeneity. These results thus imply that a nanoscopic manipulation of the Fe–As active layer, rather than its isotropic structural tuning, is the key parameter to control the superconducting properties of the iron-based systems.