The calcium doping effects on the structural and electrical properties of NdFeAsO0.8F0.2

TL;DR

This study investigates how calcium doping affects the structural and superconducting properties of NdFeAsO0.8F0.2, revealing that increased calcium content reduces the superconducting transition temperature and induces structural distortions.

Contribution

It provides experimental insights into the solubility limit, structural changes, and superconducting behavior due to calcium substitution in NdFeAsO0.8F0.2.

Findings

Superconducting transition temperature decreases with calcium doping.

Lattice parameter c and cell volume decrease as calcium content increases.

Microstrain increases with higher calcium doping.

Abstract

We have investigated experimentally how properties of NdFeAsO0.8F0.2 superconductor affected due to the substitution of the calcium by the neodymium. We have synthesized polycrystalline Nd1-xCaxFeAsO0.8F0.2 samples with x=0, 0.01, 0.025, 0.05 and 0.1 through the one step solid state reaction method. The X-ray diffraction patterns, refined using the MAUD software and Rietveld s method, have indicated the formation of tetragonal structure with the space group P4/nmm:2. We studied various structural parameters such as lattice parameters, bond angles, bond length, and etc. Based on the XRD data refinement, we have determined the upper limit of the calcium solubility in Nd-1111 structure and it is restricted to x 0.05. Also, we found that the lattice parameter a was almost constant by increasing the calcium content, while the lattice parameter c and the cell volume decreased. Based on XRD data analysis, we have inference that these are due to the variations in the bond angles of As-Fe-As {\alpha} and \b{eta} and a decrease in the bond lengths upon increasing x. So, we have expected that the superconducting transition temperature will be sensitive to the calcium doping. Experimentally, the superconducting transition temperature was reduced from 55K (x = 0) to 48K (x = 0.01) and disappeared for other samples. On the other hand, it can be concluded from our study results about of the structural and electrical properties, which the superconducting transition temperature decreased with increasing the distortion of FeAs4-tetrahedrons from regular one. Also, based on Williamson-Hall equation, the microstrain of the samples increased upon increasing x and for Nd0.95Ca0.05FeAsO0.8F0.2 sample was grown approximately three times in comparison to the pure sample. So, it is noticeable that there is a relation between the structural properties and superconductivity in our samples.