Microstructure of as-grown fully oxygenated epitaxial YBa₂Cu₃O_7-δ thin films: A transmission electron microscopy study

Abstract

Epitaxial YBa₂Cu₃O_7-δ(YBCO)thin films grown by magnetron sputtering on MgO(001) substrate have been studied by transmission electron microscopy (TEM). The films are fully oxygenated during their growth. Slowly and rapidly cooled samples, both showing good superconducting properties, have been prepared. The high-resolution and moiré fringe TEM methods have been used to analyse the microstructure and to estimate the orthorhombicity of the samples. The rapidly cooled samples show the presence of a superconducting O₇ (δ= 0) tetragonal phase, which is not ordered and where unrelaxed lattice strains are revealed by the curvature of the lattice planes. In both samples the twin boundaries are broaden and the high-resolution TEM contrast reveals a dense superposition of the twin domains in the thickness of the c-perpendicular YBCO grains.