Coexistence of grains with differing orthorhombicity in high quality YBa2Cu3O7−δ thin films

Abstract

High quality films of YBa₂Cu₃O_7−δ on LaAlO₃ have been grown by pulsed‐laser deposition at oxygen pressures of 3.4–54 Pa (25–400 mTorr). X‐ray diffraction reveals the coexistence of grains that align with the substrate axes (axial grains) and grains that are rotated by 0.4° from the substrate axes (diagonal grains). The axial grains are tetragonal while the diagonal grains achieve lattice parameters close to bulk YBa₂Cu₃O₇. The relative proportion of axial grains accounts for the measured variations of normal‐state conductance and superconducting critical current density from film to film, based on a simple two‐dimensional model of randomly positioned, insulating axial grains.