Optimal growth conditions for GdBa2Cu3O7 thin-film coated conductors characterized by polarized Raman scattering spectroscopy

Abstract

High temperature superconducting GdBa2Cu3O 7 (GdBCO) thin films were grown by pulsed laser ablation. Textured MgO on metal substrates was used as a template for second generation wire applications. Growth conditions of GdBCO thin films were investigated for substrate temperature (Ts) and oxygen partial pressure (PO 2) during deposition. Superconducting critical currents of the films were obtained in the films grown at 790-810 °C of Ts and at 100-700 mTorr of PO2. Scanning electron micrographs of the films revealed uniform and well-connected grains with some outgrown structures. X-ray θ-2θ scans of the films grown at 810 °C and 300-500 mTorr exhibited c-axis oriented texture. In-plane alignment and c-axis mosaic spread of the films were determined from X-ray Φ scans and rocking curves, respectively. Polarized Raman scattering spectroscopy was used to characterize optical phonon modes, oxygen content, cation disorder, and some possible second phases of the films. The Raman spectra of the films with large critical current density showed modes at 326-329 cm-1, 444-447 cm-1, 500-503 cm-1 related to vibration of oxygen atoms. Origin of small peaks near 600 cm-1 will be discussed as well. The information obtained from Raman scattering measurements will be useful for quality control of the conductors as well as optimization of the process conditions. © 2010 Elsevier B.V. All rights reserved.