YBCO/Nd₂CuO₄/NiO/Ni coated conductors fabricated by liquid phase epitaxy based techniques

Liquid phase epitaxy (LPE) has a great potential in producing low-cost, high-current, coated conductors due to its fast growth rate in excess of 1 μm min^-1 and the capability of growing thick films up to 10 μm without degrading the structural perfection or J_c. The main problem for LPE is the chemical reaction between the films and substrates at elevated growth temperatures. Former efforts have been focused on the reduction of growth temperatures. This has been proved to be unsuccessful due to the limited degree of temperature reduction; reducing the growth temperature also reduces the solubility of YBCO in the liquid, making the growth even more difficult. An alternative solution to this problem is to search for a special buffer which is particularly resistant to the attack of the high-temperature liquid. We have recently developed a new buffer, Nd₂CuO₄, which was very stable in the cuprate solution at temperatures around 950°C and therefore extremely useful for LPE. Initial growth of YBCO on Nd₂CuO ₄ buffered, surface oxidized Ni substrates showed a sharp superconducting transition at 90 K and transport J_c over 10 ⁵ A cm^-2 (77 K). Although YBCO could be grown on Nd ₂CuO₄ by LPE without any other intermediate seed layer, growth of Nd₂CuO₄ on both sides of the NiO/Ni substrate with 100% coverage was not easy and had a low success rate. Complete coverage of Nd₂CuO₄ buffer on the NiO/Ni substrates was the critical step to avoid Ni contamination and achieve a high J_c.