Order-disorder effect of A-site and oxygen-vacancy on magnetic and transport properties of Y1/4Sr3/4CoO3-delta

TL;DR

This study explores how A-site and oxygen-vacancy ordering influence the magnetic and transport properties of Y1/4Sr3/4CoO3-delta, revealing novel structures and their effects on ferromagnetism.

Contribution

It provides a comparative analysis of ordered and disordered Y1/4Sr3/4CoO3-delta, highlighting the impact of vacancy and oxygen ordering on physical properties and structural phases.

Findings

A-site ordering leads to unconventional oxygen-vacancy structures.

Oxygen vacancy ordering correlates with room-temperature ferromagnetism.

Disordered YSCO exhibits brownmillerite-type structures near delta=0.5.

Abstract

We have synthesized A-site ordered (AO)- and A-site disordered (AD)-Y1/4Sr3/4CoO3-delta (YSCO) with various oxygen deficiency delta, and have made a comparative study of the structural and physical properties. We have found that A-site (Y/Sr) ordering produces the unconventional oxygen-vacancy ordered (OO) structure, and that the magnetic and transport properties of both AO- and AD-YSCO strongly depend on the oxygen-vacancy (or excess oxygen) ordering pattern. AO-YSCO with a stoichiometric delta of 0.5 has the unconventional OO structure reflecting Y/Sr ordering pattern. With decreasing delta from 0.5, the overall averaged OO structure is essentially unchanged except for an increase of occupancy ratio for the oxygen-vacant sites. At delta = 0.34, excess oxygen atoms are ordered to form a novel superstructure, which is significant for the room-temperature ferromagnetism of AO-YSCO. In AD-YSCO, on the other hand, the quite different OO structure, which is of a brownmillerite-type, is found only in the vicinity of delta = 0.5.