Josephson junctions with bulk YBa/sub 2/Cu/sub 3/O/sub 7-x/, Bi/sub 2/Sr/sub 2/CaCuO/sub x/, and Tl/sub 2/Ca/sub 2/Ba/sub 2/Cu/sub 3/O/sub 10+x/

The characteristics of point contacts with combinations of Pb, YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO), Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ (BSCCO), and Tl/sub 2/Ca/sub 2/Ba/sub 2/Cu/sub 3/O/sub 10-x/ (TBCO) have been measured in a shielded liquid helium dewar. By forming several junctions of a kind the authors have extracted typical features of the current-voltage characteristics for each combination. Zero-voltage currents were observed in all cases. Diffraction patterns in the dependence of the critical currents on the applied magnetic field were found in some junctions of each kind. Therefore electron-pairs rather than single electrons are responsible for the current transport in all three oxide superconductors mentioned above. For point contacts using the high-T/sub c/ materials only, both homo- and hetero-junctions were investigated. The authors observed Josephson effects above liquid nitrogen temperatures. Whereas YBCO and TCBO were found to perform very similarly, junctions with BSCCO yielded considerably different results. All junctions behaved like weak link bridge structures