IN-SITU DEPOSITION OF YBCO/CeO₂ ON BIAXIALLY TEXTURED Ni ALLOY TAPES BY THERMAL COEVAPORATION

Abstract

We report on the in-situ preparation and characterization of coated conductors consisting of a ≈ 400 nm thick YBCO superconducting film grown by thermal co-evaporation on a ≈ 200 nm thick CeO2 buffer layer grown by e-beam evaporation on biaxially textured Ni-Cr and Ni-V substrates. We studied the degree of texture of both YBCO and CeO2 layers as a function of substrate temperature during deposition and of oxygen partial pressure. X-ray diffraction patterns reveal that the highest degree of (100) texture of the buffer layer, necessary for the subsequent growth of the YBCO film with the desired c-axis orientation, is achieved at substrate temperatures of the order of 670-730°C. The backfilling of the chamber with oxygen during the cooling-down of the substrates after deposition of the CeO2 layer greatly improves the degree of crystallization of the buffer layer. YBCO films show good superconducting properties with critical temperatures Tc of the order of 87 K. Work is in progress to scale up the process for long tapes.

Phase equilibrium in the cerium-poor Ce–Ni–Cu system

“…In the conductors of the second generation, the superconducting phase is coated on a metallic substrate with a buffer layer which has at least three functions: diffusion barrier, texture transfer and lattice matching. Presently textured Ni and Ni-Cu alloys have been successfully used with textured CeO 2 as a buffer layer, deposited by various methods [1][2][3][4][5][6]. In order to reduce the cost of production, we imagined a new concept which consists to promote the buffer layer by selective oxidation of the textured metallic tapes.…”