The effect of Yb addition in Bi₂Sr₂Ca _1-xYb_xCu₂O_y partial melted thick films

To study the phase relations in the Bi-2212 and Yb₂O₃ system, Bi₂Sr₂Ca_1-xYb_xCu ₂O_y thick films are prepared by partial melt processing via an intermediate reaction between Bi-2212 and Yb₂O₃. When Bi-2212 and Yb₂O₃ are partially melted and then slowly cooled, solid solutions of Bi₂Sr₂Ca _1-xYb_xCu₂O_y, form by reactions between liquid and solid phases which contain Yb. Following these reactions, Ca is partially replaced in Bi-2212 matrix and participates in the formation of secondary phases, such as Bi-free, (Ca, Sr)O_x and CaO. Variation of the Bi-2212-Yb₂O₃ ratios and processing parameters changes the balance between the phases and leads to different Yb:Ca ratios in the Bi-2212 matrix of processed thick films. When the partial melting process is optimized for each sample to minimize the growth of secondary phases, x = 0.42-0.46 for the samples prepared at pO₂ = 0.01 atm, x = 0.24-0.29 for the samples prepared at pO₂ = 0.21 atm, x = 0.18-0.23 for the samples prepared at pO₂ = 0.99 atm are obtained regardless to the starting compositions. It is found that superconducting properties of Bi ₂Sr₂Ca_1-xYb_xCu₂O _y thick films strongly depend on the processing conditions, because the conditions result in different Yb content in the Bi-2212 matrix and the volume fraction of the secondary phases. The highest T_c(0) of 77, 90 and 91 K were obtained for the samples processed at 0.01, 0.21 and 0.99 atm of O₂, respectively.