Effect of Structural Parameters on Superconductivity in Fluorine-Free LnFeAsO1-y (Ln=La,Nd)

TL;DR

This study investigates how structural parameters like bond lengths and tetrahedron shape influence superconductivity in fluorine-free LnFeAsO$_{1-y}$ compounds, revealing that optimal tetrahedron regularity correlates with higher transition temperatures.

Contribution

It provides detailed structural analysis and establishes the superconducting phase diagram as a function of oxygen content in LnFeAsO$_{1-y}$, highlighting the relationship between tetrahedron shape and Tc.

Findings

Superconducting transition temperature peaks with regular FeAs$_4$-tetrahedrons.

As-Fe bond length indicates covalent bonding.

Oxygen deficiency affects tetrahedron shape and superconductivity.

Abstract

The crystal structure of LnFeAsO$_{1-y}$ (Ln = La, Nd) has been studied by the powder neutron diffraction technique. The superconducting phase diagram of NdFeAsO$_{1-y}$ is established as a function of oxygen content which is determined by Rietveld refinement. The small As-Fe bond length suggests that As and Fe atoms are connected covalently. FeAs$_4$-tetrahedrons transform toward a regular shape with increasing oxygen deficiency. Superconducting transition temperatures seem to attain maximum values for regular FeAs$_4$-tetrahedrons.