Abstract: Electroconductive composite metal powders comprising flat non-noble metal powders, each covered with a noble metal in an amount of 2 to 30% by weight in average based on the weight of the non-noble metal powders, on 50% or more in average of the whole surface area of the non-noble metal powders, interposing a layer of a mixture of the non-noble metal and noble metal between each non-noble metal powder and a noble metal covering layer, are suitable for providing an electroconductive paste after mixing with a binder, said paste showing excellent electroconductivity and prevention of migration.

Abstract: An electroconductive paste for forming an electric circuit which is low in resistivity, high in electroconductivity and minimized in change of resistivity even after a thermal shock test and/or a humidity and DC applied test, can be obtained by using a composite electroconductive powder comprising a flake-like electroconductive powder made of a material such as silver, a silver alloy, a silver-coated copper powder or a silver-coated copper alloy powder and an unsteady-shaped electroconductive powder such as a reduced silver powder.

Abstract: Electroconductive composite metal powders comprising flat non-noble metal powders, each covered with a noble metal in an amount of 2 to 30% by weight in average based on the weight of the non-noble metal powders, on 50% or more in average of the whole surface area of the non-noble metal powders, interposing a layer of a mixture of the non-noble metal and noble metal between each non-noble metal powder and a noble metal covering layer, are suitable for providing an electroconductive paste after mixing with a binder, said paste showing excellent electroconductivity and prevention of migration.

Abstract: An oxide superconductor of the formula: Bi.sub.1.0 Sr.sub.A Ca.sub.B Mg.sub.C Ba.sub.D Cu.sub.1.0.+-.0.15 O.sub.X wherein A=0.6-1.3, B=0.3-0.9, C=0.01-0.3 and D=0.01-0.3 in atomic ratio, having a 2212 phase with a critical temperature of making electrical resistance zero at about 80K or more, can be produced by firing preferably at 820.degree.-870.degree. C. in a lower oxygen content atmosphere.

Abstract: The present invention provides an oxide superconductor which is mainly composed of bismuth, lead, strontium, calcium, magnesium, and copper and has the composition represented by the formula:Bi.sub.1-A Pb.sub.A Sr.sub.1-B Mg.sub.B Ca.sub.1 Cu.sub.1.7.+-.0.3 Oxwherein A=0.15-0.35 and B=0.05-0.3 in which numerals represent atomic ratio and an oxide superconductor which is mainly composed of bismuth, lead, strontium, calcium, magnesium, barium and copper and has the composition represented by the formula:Bi.sub.1-A Pb.sub.A Sr.sub.1-(B+C) (Mg.sub.B Ba.sub.C)Ca.sub.1 Cu.sub.1.7.+-.0.3 Oxwherein A=0.15-0.35, B=0.05-0.3 and C=0.02-0.2 in which numerals represent atomic ratio. Methods for producing these superconductors are also provided.

Abstract: A superconducting thick film circuit board or thick film superconductor obtained by forming a rod-like crystal superconducting composite layer comprising a superconductor made of a compound of M-Ba-Cu-O, M being Y and/or a lanthanide element, and a composite of Ag and Pt on a stabilized zirconia substrate has a high Jc value and good superconducting properties.