Physica C 162-164 (1989) 641-642 North-Holland EFFECT OF Pb DOPING ON 110K PHASE FORMATION IN BiSrCaCuO THIN FILMS J. Wosik,* M. F. Davis,* J. C. Wolfe,* R. Kranenburg,* J. Wlilliams,* Y. Y. Sun* * and P. H. Hor** Texas Center for Superconductivity at University of Houston, Houston, Texas 77204-5506 * Electrical Engineering Department. **Physics Department. This paper presents a study of the effect of Pb doping on the formation of the 110K phase in 2:1:2:2 and 2:2:2:3 composition BiCaSrCuO thin films deposited by an electron beam flash evaporation technique. Experiments with 2:2:1:2 films showed that Tco increased from 76K without doping to 81K with Pb doping but no evidence of 110K phase formation was found. Results for 2:2:2:3 films prepared without Pb doping include10% drops in resistivity at 110K when annealed for at least 6 hour time periods. Lead doped 2:2:2:3 films have displayed large resistivity drops at 115K with Tco at 80K. Millimeter wave cavity measurements and XRD have shown these films to be about 10% 2223 phase. The rate of Pb loss during annealing and the eutectic behavior were studied along with various annealing conditions to optimize conditions that yield the 110K phase in these films. It is now well known 1 that the Bi2Sr2CanCUn+lO6+2n+x system contains at least three distinct superconducting phases. The process for the formation of 2201 (n=0, Tc around 22K) and 2212 (n=l, Tc around 80K ) single phases is well known, 1,2 but the 2223 phase (n=2, Tc around 115 K) is usually intergrown with the 2212 phase. We have studied the influence of Pb on the formation of 2212 and 2223 phases using two different initial film compositions. The 0.65 I~m thick films were deposited onto MgO substrates at a temperature 200°C using an electron beam flash evaporation (EBFE) technique that has been described in detail elsewhere 3. Lead composite films were produced by first depositing a layer of Pb and then flash evaporating the BiSrCaCuO material without breaking vacuum. Annealing of films was performed in a quartz tube furnace in flowing oxygen. Heating and cooling rates were 40°C/min and 4°C/min, respectively, for all samples. Undoped 2:2:1:2 films annealed at temperatures from 850-870°C displayed Tc (R=0) values no higher than 77 K. Composite films with approximately 6% Pb, however, required lower annealing temperatures (850°C-860oc) to obtain 81 K Tc (R=0) values consistently. XRD showed that 0921-4534/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland) these films were almost pure phase and c- axis oriented. There was no evidence in resistance curves or XRD data that the 2223 phase was present iri either the undoped or doped 2:2:1:2 films. Lead composite 2:2:2:3 films deposited with a variety of Pb concentrations were annealed under various conditions. Shown in Figure 1 are the three types of resistive transitions that were observed in these films. Normal state resistivity was about lmQ- cm. 1.2 1.0, t-- 0.8. o~ 0.6" e- • ~ 0.4 • n- 0.2 0.0 6o ------ i__ ~i~i~i:!~l i 70 80 90 100 110 120 130 Temperature [K] FIGURE 1 Resistive transition curves (normalized to T=120K) typical for Pb-doped 2:2:2:3 films.