Bernhard Hettich

The influence of the phase equilibria on the critical temperatures T C of the high-T C Bi-Sr-Ca-Cu-O and Y-Ba-Cu-O compounds

The phase equilibria of YBa2Cu3O7−d (123 phase) strongly influence its oxygen content and consequently its critical temperature Tc. With increasing content of BaCuO2 or CuO, Tc decreases. Whereas, if Y2BaCuO5 (211 phase) is in equilibrium with the 123 phase, the oxygen content and Tc of which is high. Bi2+x(Sr,Ca)3Cu2O8+d exhibits an extended single phase region and its Tc is strongly affected by its chemical composition. In addition, the oxygen content of the phase is a function of the temperature and influences the Tc of the phase.

The phase equilibria of Bi2Sr2Ca2Cu3O10 in the system Bi2O3SrOCaOCuO

Abstract The phase equilibria of the system Bi2O3SrOCaOCuO with emphasis on the High-Tc superconducting compound Bi2Sr2Ca2Cu3O10 have been studied. For the preparation of single phase Bi2Sr2Ca2Cu3O10-samples the exakt stoichiometry is not likely, because it is not stable. For the processing of Bi2Sr2Ca2Cu3O10-samples the preparation of samples exhibiting a little excess of CuO and Bi2O3 is recommended.

Increased pinning in “Bi2Sr2CaCu2O8” ceramics

Abstract From a consideration of the phase equilibrium diagram of the system Bi 2 O 3 -SrO-CaO-CuO, a simple annealing procedure was developed to transform single phase 2212 ceramics with compositions Bi 2.18 Sr 1.75 Ca 1.25 Cu 2 O 8+ d and Bi 2.3 Sr 2 CaCu 2 O 8+ d into multi phase samples containing Ca 2 CuO 3 and/or liquid. The transformations result in increases of the critical current densities at 1 T of 5–10 times, which is believed to reflect the increased pinning properties of these ceramics. The exact nature of the resulting pinning centres has not been determined yet.

Melt processing and oxygen doping of bismuth superconductors

Abstract Bi based superconductors with 1, 2 and 3 CuO2-layers have been prepared with Tc values of 60–75 K, 80–90 K and 100–110 K, respectively. The compounds Bi2(Sr, Ca)2CuO6+x and Bi2Sr2CaCu2O8+x were synthesized by special melt processes. Melt processed Bi2Sr2CaCu2O8+x can be obtained as a dense bulk material which carries current densities in the range of 10,000 A/cm2 uo to 8 T magn. field at 4 K.