Thallium-basierende Hochtemperatur Supraleiter

The discovery of superconductivity in copper oxides, which after doping with additional oxides of the alkaline earth and rare earth elements, yielded compounds for which below a certain temperature, the so-called critical temperature, the electric resistance becomes too small to be measured, led to intensive research activities. In the frame of the project superconducting compounds were fabricated and studied, which are based on thallium, lead bismuth, calcium, strontium, rare earth and copper oxides. The main advantage of these compounds are the critical temperatures of 110 K to 120 K (- 163 to - 153 C), temperatures well above the boiling point of nitrogen. This allows cooling with nitrogen rather than with helium necessary for classical superconductors. Fabrication of thallium-based superconducting material from a variety of precursor oxides is a challenging task. During this project fabrication methods and heat treatment procedures were developed which resulted in almost phase pure polycrystalline superconducting material with low porosity. The samples were characterized in Linz and in cooperation with scientists in Vienna, Krakow, Budapest and Bratislava with respect to the electrical and magnetic properties as well as with respect to mechanical behavior and the microstructure. Critical current densities greater than 7 000 A/cm2 at -196 C and tapes with critical current densities of 20 000 A/cm2 for polycrystalline material have been measured. Possible future application are the transport of electricity, transportation via levitation, frictionless motors, fault current limiters, transformers and filters in high-frequency applications.