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.