Isovalent substitution effects of arsenic on structural and electrical properties of iron-based superconductor NdFeAsO0.8F0.2

TL;DR

This study investigates how substituting arsenic with phosphorus and antimony in NdFeAsO0.8F0.2 affects its structure and superconducting properties, revealing changes in critical temperature and lattice parameters.

Contribution

It provides new insights into the effects of isovalent P and Sb substitution on the structural and superconducting properties of NdFeAsO-based superconductors.

Findings

Superconducting transition temperatures of 56K and 46K for Sb and P doped samples.

Structural transition temperature at 140K for P-doped sample.

Lattice shrinkage correlates with superconductivity changes.

Abstract

In this paper, nominal compositions of NdFeAsO0.8F0.2, NdFeAs0.95Sb0.05O0.8F0.2 and NdFeAs0.95P0.05O0.8F0.2 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) and occupancy of ions and lattice parameters were changed by isovalent substitution of Phosphorus P and Antimony Sb in the NdFeAsO0.8F0.2 sample. The alfa and beta bond angles and Fe-As bond length are changed from the corresponding value of alfa and beta 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 56K and 46K for NdFeAsO0.8F0.2, NdFeAs0.95Sb0.05O0.8F0.2, respectively. The NdFeAs0.95P0.05O0.8F0.2 showed the structural transition temperature at 140K. 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.