Development of Biaxially Texture-Coated Superconductors Based on Copper and Copper Alloys

Abstract : The overall program goal was to develop a new class of biaxially textured YBCO conductors using copper or copper-alloys as substrates. To accomplish this goal, the following program tasks were performed: (1) the processing of thin buffer layers on copper-based substrates as epitaxial templates and diffusion barriers, and (2) the optimization of buffer-layer structures from the current state-of-the-art multilayer system to a 1-to-2 layer system by enhancing the adhesion between buffer layers and copper-based substrates. The primary focus of this project was to grow high-Tc (Y123) films on textured copper substrates using TiN and WN buffer layers. The authors developed a method to grow self-aligned epitaxial MgO/Cu/MgO films on silicon substrates using a pulsed laser deposition (PLD) technique. A thin layer of Cu/Mg (Mg 5%) was deposited using PLD over Si and Cu specimens followed by annealing in a controlled oxygen environment, which resulted in the segregation of Mg on either side of the copper film. In addition, they also demonstrated the feasibility of growing WN buffer layers using ion implantation techniques. High-resolution transmission electron microscopy (HRTEM) measurements showed thin layers of nitride films act as a diffusion barrier and inhibit the diffusion of Cu into the system. These approaches have been demonstrated to be useful for growing high-quality, epitaxial YBa2Cu3O7_d films for Cu- or Cu alloy-based superconducting devices.