Intercalation and Staging Behavior in Super-Oxygenated $La_2CuO_{4 + \delta}$

TL;DR

This study investigates the structural superlattice formations in super-oxygenated La2CuO4+δ, revealing how interstitial oxygen layers induce tilt changes in CuO6 octahedra, advancing understanding of its superconducting properties.

Contribution

It introduces a structural model explaining superlattice peaks in La2CuO4+δ based on interstitial oxygen ordering and octahedral tilt boundaries, clarifying previous observations.

Findings

Identification of superlattice peaks indicating new periodicities

A model linking interstitial oxygen layers to octahedral tilt changes

Clarification of La2CuO4+δ as a lamellar superconducting system

Abstract

A high temperature electrochemical oxidation process has been used to produce large single crystals of $La_2CuO_{4 + \delta}$ suitable for neutron scattering experiments. Below room temperature the oxygen-rich phases have structural superlattice scattering peaks which indicate new periodicities ranging from 2 to 6.6 layers perpendicular to the copper oxide planes. A model structure originally proposed for $La_2NiO_{4 + \delta}$ can account for the superlattice peaks as a result of anti-phase domain boundaries between different tilt directions of the CuO$_6$ octahedra. Within this model, the changes in CuO$_6$ tilt directions are induced by segregated layers of interstitial oxygen which order in a manner similar to intercalants in graphite. This structural model thus clarifies previous work and establishes $La_2CuO_{4 + \delta}$ as a unique lamellar superconducting system with annealed disorder.