Application of top seeding in the melt processing of Nd123 thick films on YSZ substrates: I buffer layer optimization

A new concept of a buffer layer in superconducting thick film technology was tested. The idea is based on increasing the NdBa₂Cu₃O_x melt viscosity at the processing temperature near the substrate by using higher ratios of Nd₄Ba₂Cu₂O_z solid phase in the first screen printed pass which is considered as a buffer layer. Different compositions, thicknesses and thermal schedules were used to optimise the buffer layer. The optimised buffer layer was employed in the fabrication of NdBa₂Cu₃O_y thick films on yttria stabilized zirconia (YSZ) substrates using the top seeding melt growth (TSMG) technique. Using the buffer layer was effective in preventing a large amount of liquid (BaCuO₂-CuO) from severe interaction with the substrate during the prolonged time in the TSMG technique. Consequently, a large superconducting single domain was obtained. Thick films were melt processed in 0.1% O₂ in Ar atmosphere to suppress the Nd_{1 + x}Ba_{2 − x}Cu₃O_y (Nd_123SS) solid solution formation. The produced thick films have high transition temperature (T_C) and improved microstructures.