Abstract: A family of mercury-containing Sr-(Ca.cndot.Y)-Cu-O superconducting materials having a zero-resistance temperature, T.sub.c(zero), greater than 90 K so that they can be cooled to and maintain the desired superconducting characteristics using relatively less expensive liquid nitrogen, are disclosed. The high-temperature superconductor is represented by the formula of: (Pb.sub.0.5 Hg.sub.0.5)(Sr.sub.2-x Ba.sub.x)(Ca.sub.0.7 Y.sub.0.3)Cu.sub.2 O.sub.7-.delta. ; wherein the value of x ranges between about 0.1 and about 0.6, preferably between about 0.2 and about 0.3. These superconducting materials are prepared by first grinding and mixing in open air constituent oxide powders of PbO, HgO, SrO.sub.2, BaO.sub.2, CaO, Y.sub.2 O.sub.3, and CuO. After mixing, the powder mixture is pressed under a pressure of about 5 ton/cm.sup.2 to form a pellet having a diameter of 8 mm and a thickness of 3 mm. Thereafter, the pressed pellet is wrapped with a gold foil (with a thickness of 0.