Experimental aspects of Alpha, Beta angles distortion on superconductivity in 1111-type Iron-based superconductor

Abstract

In this research, we aim to clarify the relationship between the structural distortion due to doping and the superconductivity existence in the FeAs4 structure. For this, we have prepared polycrystalline of NdFeAsO_0.8F_0.2, NdFeAs_0.95Sb_0.05O_0.8F_0.2 and Nd_0.99Ca_0.01FeAsO_0.8F_0.2 samples by one-step solid state reaction method. The structural and electrical properties of the samples were characterized through the X-ray diffraction pattern and the 4-probe method, respectively. The XRD patterns, refined using the MAUD software and Rietveld's method, have indicated formation of the tetragonal structure with the space group P4/nmm:2. The variation of the lattice structuralparameters for the NdFeAsO_0.8F_0.2 doping with Sb and Ca ions were obtained by the Rietveld refinement. The changes of bond lengths and the ⍺, β bond angles have been specified from the corresponding value of ⍺ and β regular FeAs4-tetrahedron with the Sb/As and Ca/Nd doping, where they affect the superconductivity existence. The α and β bond angles increase and decrease with the substitution of Sb/As and Ca/Nd doping, which leads to the<br />contraction of the FeAs layer, and therefore the lattice parameter “c" decreases. The superconducting transition temperature was reduced from 56 K for NdFeAsO_0.8F_0.2 sample to 48 K and 46 K for Ca/Nd and Sb/As doping, respectively. It can be concluded from the structural and electrical properties that the superconducting transition temperature decreases with increasing the distortion of FeAs4-tetrahedron from the regular one. So, there is a relation between the structural properties and the superconductivity in the iron based superconductors-1111 regardless of the doping procedures.