Electronic Properties and Current Carrying Capacity of High-Temperature Ceramic Superconductors

摘要

Samples of both the YBa2Cu3O7 family of high-temperature ceramic superconductor and the layered set of bismuth based superconductors, described by the set of crystal structures Bi2Sr2Ca(n-1)CunO(2n+4+delta), were synthesized and characterized by x ray diffraction, and temperature dependent resistivity and thermoelectric-power measurements. Superconductivity in the yttrium-based materials is relatively insensitive to rare earth substitutions for the yttrium. Critical current measurements on these materials reveal two characteristic critical current values. The intrinsic critical current, determined by the suppression of the transition midpoint, is estimated to be greater than 10,000 A/sq cm at 77K. The critical current defined by the R=0 point is much less in bulk ceramics and limited by intercrystalline weak links. For the bismuth based materials, two high-temperature superconducting phases have been observed with transition temperatures near 80 K and 110 K. Evidence from thermorelectric power measurements is presented which shows both electronlike and holelike carriers contribute to the electrical transport in this family of ceramic superconductors. However, all of superconducting transitions observed involve with transition temperatures near 80 K and 110 K. Evidence from thermoelectric power measurements is presented which shows both electronlike and holelike carriers contribute to the electrical transport in this family of ceramic supercondutors. However, all of the superconducting transitions observed involve holelike states. Keywords: Ceramic superconductors; Bismuth based superconductors; Holelike carriers; Copper oxides; Calcium compounds; Strontium compounds. (JHD)