Intercalation and Staging Behavior in Super-Oxygenated $L{a}_{2}Cu{O}_{4+\delta }$

Abstract

A high temperature electrochemical oxidation process has been used to produce large single crystals of $L{a}_{2}Cu{O}_{4+\delta }$ 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 $L{a}_{2}Ni{O}_{4+\delta }$ 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 $L{a}_{2}Cu{O}_{4+\delta }$ as a unique lamellar superconducting system with annealed disorder.

23 pages, latex, 6 figures (not including Figures 2 & 7 and Table 1 which were not submitted but are available upon request to the Authors at: [email protected])