A.Y. Ilyushechkin

The effect of Yb addition in Bi2Sr2Ca1−xY bxCu2Oy partial melted thick films

To study the phase relations in the Bi-2212 and Yb2O3 system, Bi2Sr2Ca1-xYbxCu2Oy 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 Bi2Sr2Ca1-xYbxCu2Oy 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 pO(2) = 0.01 atm, x = 0.24-0.29 for the samples prepared at pO(2) = 0.21 atm, x = 0.18-0.23 for the samples prepared at pO(2) = 0.99 atm are obtained regardless to the starting compositions. It is found that superconducting properties of Bi2Sr2Ca1-xYbxCu2Oy 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 O-2, respectively.

Re-melting of Bi-2212/Ag laminated tapes by partial melting process

Abstract Bi-2212 tapes are prepared by a combination of dip-coating and partial melt processing. We investigate the effect of re-melting of those tapes by partial melting followed by slow cooling on the structure and superconducting properties. Microstructural studies of re-melted samples show that they have the same overall composition as partially melted tapes. However, the fractional volumes of the secondary phases differ and the amounts and distribution of the secondary phases have a significant effect on the critical current. Critical current of Bi-2212/Ag tapes strongly depends on the maximum processing temperature. Initial J c s of the tapes, which are partially melted, then slowly solidified at optimum conditions and finally post-annealed in an inert atmosphere, are up to 10.4×10 3 A/cm 2 . It is found that the maximum processing temperature at initial partial melting has an influence on the optimum re-heat treatment conditions for the tapes. Re-melted tapes processed at optimum conditions recover superconducting properties after post-annealing in an inert atmosphere: the J c values of the tapes are about 80–110% of initial J c s of those tapes.

Continuous production of Bi-2212 thick film on silver tape

Bi-2212 thick film on silver tapes are seen as a simple and low cost alternative to high temperature superconducting wires produced by the Powder In Tube (PIT) technique, particularly in react and wind applications. A rig for the continuous production of Bi-2212 tapes for use in react and wind component manufacture has been developed and commissioned. The rig consists of several sections, each fully automatic, for task specific duties in the production of HTS tape. The major sections are: tape coating, sintering and annealing. High temperature superconducting tapes with engineering critical current densities of 10 kA/cm/sup 2/ (77 K, self field), and lengths of up to 100 m have been produced using the rig. Properties of the finished tape are discussed and results are presented for current density versus bend radius and applied strain. Depending on tape content and thickness, irreversible strain /spl epsi//sub irrev/, varies between 0.03 and 0.1%. Cyclic bending tests when applied strain does not exceed /spl epsi//sub irrev/, showed negligible reduction in J/sub c/ along the length of the tape.

Melt textured Y123 bulk and thick film

Abstract YBa 2 Cu 3 O 7−δ - 25mol%Y 2 BaCuO 5 bars and thick films have been melt textured using a stationary furnace with a temperature gradient of 3 or 6 °C/cm. Samples are heated above the peritectic reaction temperature and quenched to just above the solidification temperature and then slowly cooled below the solidification temperature. All bar shaped samples consist of 2∼5 mm grains though the grain orientations strongly depend on the heat treatment conditions. The bar shows the maximum J c of above 3000 A/cm 2 , whereas the maximum J c of 200 A/cm 2 and T c zero of 88 K are obtained for the thick film on (100) LaAlO 3 single crystal.

Bi-2212/Ag laminated tapes : bending and joining effects

Abstract Superconducting composite Bi-2212/Ag tapes and their joints are fabricated by a combination of dip-coating and partial melt processing. The heat treated tapes have a critical current ( I c ) between 8 and 26 A, depending on tape thickness and the number of Bi-2212 layers. Current transmissions between 80% and 100% have been achieved through the joints of tapes. Different types of HTS joints of Bi-2212/Ag laminated tapes are made and their transport properties during winding operations are investigated. Irreversible strain values ( e irrev ) for laminated tapes and their joints are determined and it is found that the degradation of I c during tape bending depends on the type of joint.