Superconductivity above 50K in LnFeAsO1-y (Ln= Nd, Sm, Gd, Tb and Dy) Synthesized by High-pressure Technique

TL;DR

This study successfully synthesized LnFeAsO1-y superconductors with various lanthanides using high-pressure techniques, revealing a maximum Tc around 50K and highlighting the importance of synthesis pressure and structural parameters.

Contribution

It demonstrates the synthesis of single-phase LnFeAsO1-y superconductors with high Tc using high-pressure methods and explores the relationship between structure and superconductivity.

Findings

Maximum Tc around 50K for heavier Ln elements.

Synthesis pressure is crucial for phase purity, especially for heavier Ln.

Lattice parameters decrease with increasing Ln atomic number.

Abstract

We have succeeded in synthesizing single-phase polycrystalline samples of oxygen-deficient oxypnictide superconductors, LnFeAsO1-y (Ln: lanthanide elements) with Ln=La, Ce, Pr, Nd, Sm, Gd, Tb and Dy using high-pressure synthesis technique. It is found out that the synthesis pressure is the most important parameter for synthesizing single-phase samples, in particular for the heavier Ln?s, such as Tb and Dy. The lattice parameters systematically decrease with the atomic number of Ln, reflecting the shrinkage of Ln ionic radius. For the lighter Ln?s (La, Ce, Pr, Nd), Tc increases monotonously with decreasing the lattice parameters from 26K for Ln=La to 54K for Ln=Nd, then stays at the constant value around 53K for the heavier counterpart (Nd, Sm, Gd, Tb and Dy). The results suggest the intimate relationship between the crystal structural parameters and the superconductivity on the one hand, as well as the possible existence of the inherent maximum Tc on the other, which is located around 50 K in the LnFeAsO based materials.