Pulsed laser deposition of REBCO
Pulsed laser deposition is used as a standard technique to prepare superconducting YBCO layers on single crystals as well as on different buffer architectures. The YBCO deposition is typically carried out in a high vacuum chamber using a KrF excimer laser and a background pressure of about 0.3 mbar oxygen. After deposition, the samples are cooled in 0.4 bar O2. The standard thickness of the YBCO layer is about 300 nm for all samples. Beside the standard on-axis geometry, also off-axis PLD is used to prepare smooth films on single crystalline substrates.
The preferred orientations and the texture of the prepared samples are investigated using X-ray diffraction. The surface structure of the YBCO layer, as determined by SEM, shows a homogeneous structure with typical pinholes (Fig. 1). The quality of the deposited YBCO layers is routinaly determined with inductive measurements of the critical temperature Tc and the critical current density Jc. The local distribution of the inductive Jc values over the sample size is measured using the CryoscanTM by THEVA. Furthermore, the critical temperature and the critical current density are measured resistively in various magnetic fields up to 14 T with a Quantum Design PPMS system by a standard four-probe method on a bridge of 500 mm (for RABiTs tapes) or 50 µm (for single crystals) width, patterned by photolithography. The magnetic field is directed parallel to c-axis and normal to current direction. An electric field criterion of Ec = 1 µV/cm is used for the determination of the critical current density. A typical example is shown in Fig. 2.
|Fig. 1||Fig. 2|
Fig.1: SEM-images of a typical YBCO layer grown on a NiO/Ni-Ag substrate using a SrTiO3/BaZrO3 buffer layer architecture
Fig.2: Magnetic field dependence of the critical current density for YBCO films grown on different substrates using a SrTiO3/BaZrO3 buffer layer architecture
R. Hühne, J. Eickemeyer, V.S. Sarma, A. Güth, T. Thersleff, J. Freudenberger, O. de Haas, M. Weigand, J.H. Durrell, L. Schultz, B. Holzapfel
Application of textured highly alloyed Ni-W tapes for coated conductor architectures
Supercond. Sci. Technol. 23 (2010) 034015
Hühne, R., Selbmann, D., Eickemeyer, J., Hänisch, J., Holzapfel, B.: „Preparation of buffer layer architectures for YBa2Cu3O7-x coated conductors based on surface oxidized Ni tapes”, Supercond. Sci. Technol. 19 (2006) 169-174
Fernandez, L., Holzapfel,B., Schindler, F., de Boer, B., Attenberger, A., Hänisch, J., Schultz, L.: „Influence of the grain boundary network on the critical current of YBa2Cu3O7 films grown on biaxially textured metallic substrates”, Physical Review B 67 (2003) 52503/1-4