Structure and transport studies on nanometer YBCO/PBCAO multilayers

We have fabricated metal (M) doped PrBa₂Cu₃O₇ (PBCO), i.e., PrBa₂(Cu_1-xM_x)₃O₇ for M = Al, Co, Fe, Ga, Ni and Zn, and x = 0.05, 0.10, 0.15, and 0.20. X-ray data indicated no significant second phase for substituting Cu by Al, Co, Fe and Ga up to 20%. However impurity phases were detected for Ni and Zn substituted samples with doping levels equal to and higher than 15%. At 77 K the electrical resistivity of these compounds is orders in magnitude higher than that of PBCO. We also found that although the lattice parameters in the doped samples differ from the undoped one, all samples remain orthorhombic. The lattice parameters of the doped sample are very close to those of YBa₂Cu₃O_7-δ (YBCO) and PBCO. For this reason these compounds are better materials to be used as the I-layer for YBCO SIS junctions [T.-P. Chen, U. Tipparach, X. Yang, A. Zhou, B. Chen, Q.Y. Chen, W.K. Chu, C.J.C. Chen, J.T. Wang. Intern. Mod. Phys. B 9 (2005) 123]. Results from transport studies on 2000 Å thick PrBa₂[Cu_0.80Al_0.2]₃O₇ (PBCAO) and YBCO/PBCAO multilayers are presented in this paper.