Isovalent Substitution Effects of Arsenic on Structural and Electrical Properties of Iron-Based Superconductor NdFeAsO0.8F0.2

Abstract

In this paper, nominal compositions of NdFeAsO 0.8 F 0.2 , NdFeAs 0.95 Sb 0.05 O 0.8 F 0.2 and NdFeAs 0.95 P 0.05 O 0.8 F 0.2 were prepared by one-step solid-state reaction method. The structural, electrical and morphological properties of samples were characterized through the XRD pattern, the 4-probe method and SEM, respectively. The crystal structure of our samples was tetragonal with P4/nmm:2 symmetry group. Also, the (x, y, z), occupancy of ions and lattice parameters were changed by isovalent substitution of Phosphorus (P) and Antimony (Sb)in the NdFeAsO 0.8 F 0.2 sample. The ⍺, β bond angles and Fe-As bond length are changed from the corresponding value of ⍺ and β regular FeAs4-tetrahedron by isovalent doping P/As and Sb/As, that they are effective on the superconductivity transition temperature. The microstrain and crystalline size of samples were studied by the Williamson Hall method. The superconducting critical temperatures were attained at 56 K and 46 K for NdFeAsO 0.8 F 0.2 , NdFeAs 0.95 Sb 0.05 O 0.8 F 0.2 , respectively. The NdFeAs 0.95 P 0.05 O 0.8 F 0.2 showed the structural transition temperature at 140 K. It seems that there is a relation between the superconductivity and shrinkage of the crystal lattice. The flake-type of grains was observed by SEM pictures of samples.

The Superconductivity Mechanism in Nd-1111 Iron-Based Superconductor Doped by Calcium

“…We used one-step solid state reaction method for synthesizing the polycrystalline samples with the nominal compositions of Nd 1-x Ca x FeAsO 0.8 F 0.2 (x=0.0, 0.01, 0.025, 0.05, and 0.1), as indicated in Refs. [46,47] Consequently and according to the mentioned theory, the S± symmetry and the spin-fluctuations are predominant against to the orbital-fluctuations in our samples. In the other work, J. Li et al [58] described that the T C would be weakly suppressed by impurities in the S++ state, because of the following reasons: (1) Suppression of the orbital-fluctuations because of the violation of the orbital degeneracy near the impurities, (2) The strong localization effect, which the mean free path is comparable to the lattice spacing.…”

“…We used one-step solid state reaction method for synthesizing the polycrystalline samples with the nominal compositions of Nd 1-x Ca x FeAsO 0.8 F 0.2 (x=0.0, 0.01, 0.025, 0.05, and 0.1), as indicated in Refs. [46,47]. The…”