PHASE EVOLUTION AND SUPERCONDUCTIVITY EMERGENCE IN REPETITIVELY ANNEALED BI-SR-CA-CU-O THIN-FILMS

Bi(Pb)-Sr-Ca-Cu-O superconducting thin films on MgO (100) substrates h ave been made by laser deposition in combination with repetitive post- annealing treatments. The films of nominal composition (Bi, Pb)2Sr2Ca2 Cu3O10+delta were deposited at 400-degrees-C and then heated in air at a rate of 75-80-degrees-C/min, held at 845-847-degrees-C for 10 min, quenched to 600-degrees-C at a rate of 80-degreesC/min, and slowly coo led at a rate of 3.3-degrees-C/min to room temperature. The Bi2Sr2CaCu 2O8+delta (2212) phase was found to crystallize first in these as-depo sited amorphous films, whereas the (Bi, Pb)2Sr2Ca2Cu3O10+delta (2223) phase was grown in large quantities by repeating the annealing cycle. With this protocol, the 2223 phase is developed more effectively than that observed in the long period of annealing, and the formation of pi nholes on the surface is significantly reduced. Surface morphologies e xamined by scanning electron microscopy (SEM) are improved for films r epetitively annealed under reduced pressure conditions. The results of magnetic susceptibility measurements on these films correspond well w ith the phase behavior seen by X-ray diffractometry (XRD) analyses. Th e transport critical current densities, J(c), of the film are 9.0x10(5 ) and 5.5x10(4) A/cm2 at 5 and 40 K, respectively. The magnetization c ritical current densities derived from M(H) data at 6 K are two orders of magnitude higher in the orientation of H perpendicular-to c-axis t han of H parallel-to c-axis. As a preliminary study, XRD line-broadeni ng analysis was performed to investigate the effects of lattice strain and crystallite size in the set of films that were annealed at variou s temperatures for 3-6 h. The microstrain values are in the range of 1 0(-4)-10(-3), and the crystallite sizes in films obtained for the 2212 and 2223 phases depend on annealing time, temperature, and cooling ra te. Microstrain associated with the 2223 phase is more sensitive to an nealing parameters. These results suggest that XRD line-broadening ana lysis may be a valuable method to study the growth mechanism and mater ial properties of the repetitively annealed films.