Second Homologous Series of Iron Pnictide Oxide Superconductors (Fe2As2)(Can+2(Al,Ti)nOy)[n = 2,3,4]

TL;DR

This paper reports the discovery of a new series of iron pnictide oxide superconductors with layered structures, demonstrating superconductivity at around 36-39 K, and highlights the potential for further superconductor development in this class.

Contribution

The study introduces a novel homologous series of iron pnictide oxides with unique layered structures, expanding the family of iron-based superconductors.

Findings

New homologous series of iron pnictide oxides identified.

Superconductivity observed at approximately 36-39 K.

Structures feature perovskite-like layers with varying sheet numbers.

Abstract

We have discovered a new homologous series of iron pnictide oxides (Fe2As2)(Can+2(Al,Ti)nOy)[n = 2,3,4]. These compounds have perovskite-like blocking layers between Fe2As2 layers. The structure of new compounds are tetragonal with space groups of P4/nmm for n = 2 and 4 and P4mm for n = 3, which are similar to those of (Fe2As2)(Can+1(Sc,Ti)nOy)[n = 3,4,5] found in our previous study. Compounds with n = 3 and 4 have new crystal structures with 3 and 4 sheets of perovskite layers, respectively, including a rock salt layer in each blocking layer. The a-axis lengths of the three compounds are approximately 3.8 A, which are close to those of FeSe and LiFeAs. (Fe2As2)(Ca6(Al,Ti)4Oy) exhibited bulk superconductivity in magnetization measurement with Tc(onset)~36 K and resistivity drop was observed at ~39 K. (Fe2As2)(Ca5(Al,Ti)3Oy) also showed large diamagnetism at low temperatures. These new compounds indicate considerable rooms are still remaining for new superconductors in layered iron pnictides.