The Properties of Screen Printed (Bi,Pb)-Sr-Ca-Cu-O Thick Films Based On Decomposed Oxalate Powders

Abstract

The significance of powder and paste characteristics was studied in order to improve the morphology and structure of superconducting (Bi,Pb)-Sr-Ca-Cu-O screen printed thick films. Powder with nominal composition of Bi_1.75Pb_0.4Sr_1.9Ca_2.1Cu_3.2O_y was prepared via the oxalate route and decomposed at 430 to 795℃. The decomposed powders were characterized by X-ray diffraction, transmission electron microscopy and specific surface area measurements. These studies showed a variation of specific surface area from 16.5 to 0.9 m₂/g and a variation of the average particle size from 100 nm to 800 nm in the studied temperature interval. The phase structure showed three distinct temperature areas; between 430 to 620, 620 to 715, and at 795℃.Thick-film pastes were made by the addition of an organic vehicle at 500, 620, 650 and 795℃ to decompose annealed oxalate synthesized powders and, for comparison, the vehicle was also added to sintered mixed-oxide/carbonate-based powder in weight ratios from 0.42 to 0.54:1. Films were screen printed on single crystal MgO (100) substrates and melt annealed at 890 to 895℃ for 3 min and subsequently, for prolonged diffusion, annealed at 852℃. After firing, the films were mainly composed of the (001) textured (Bi,Pb)₂Sr₂Ca₂Cu₃O_y phase. The reference films, made from mixed oxide/carbonate powder, resembled the films based on oxalate powders decomposed at 795℃. Films based on oxalate powders, decomposed at lower temperatures, were smoother and were able to carry noticeably higher currents than films based on powders decomposed at higher temperatures.