Lead-doped electron-beam-deposited BiSrCaCuO superconducting thin films☆

Abstract Superconducting thin films of the lead-doped BiSrCaCuO system have been prepared on (100) single-crystal SrTiO 3 substrates by an electron beam deposition technique using a single sintered pellet as the evaporation source. As-deposited films are amorphous and non-superconducting; post-deposition annealing at an optimized temperature in air has been found to result in crystalline and superconducting films. The superconducting characteristics of the films have been observed to be sensitive not only to the duration and temperature of post-deposition annealing but also to the lead content and the sintering parameters for the pellet to be used as the evaporation source. A pellet with nominal composition Bi 3 Pb 1 Sr 3 Ca 3 Cu 4 O y that had been sintered for 200 h zero resistivity at T c 0 = 112 K . However, films deposited using such a pellet as the evaporation source had T c 0 ≈ 73–78 K, as had the films deposited from a pellet without any lead. We investigated systemativally films deposited from pellets with more lead and sintered for different durations. It is evident from these investigations that pellets with nominal composition Bi 3 Pb 2 Sr 3 Ca 3 Cu 4 O y , i.e. with an excess of lead, and sintered for about 75 h when used as the evaporation source yield films with T c 0 ≈ 100 K when annealed between 835 and 840 °C for an optimized long duration. The films are characterized by X-ray diffraction and energy-dispersive spectroscopy techniques and have been found to be highly c axis oriented. The effect of lead in promoting a high T c 0 = 110 K phase seems to be similar to that in bulk ceramics.