High pressure study on heterogeneous superconducting materials

The study of heterogeneous superconductors has been a subject of great interest for the last several years because of the wide range of electrical properties of this class of material and thus the opportunities provided by this class of material for the research on problems of both academic and practical significance. The author investigated two systems of this kind under high pressure, namely: the BaPb/sub 1-x/Bi/sub x/O3 compounds near a metal-semiconductor phase boundary and the Al-Si eutectic alloys. Both are unusual in the sense that the former possesses a high superconducting transition temperature T/sub c/ approx. 13 K, irrespective of the highly oxidized state of the compound and the absence of any transition metal elements in the compound, and the latter exhibits a T/sub c/ approx. 5.5 K in contrast to the low T/sub c/ approx. 1.17 K of Al and the non-superconductivity of Si. It was found that Josephson coupling exists in the sintered BaPb/sub 1-x/Bi/sub x/O3 compounds, suggesting that these compounds are, more often than not, heterogeneous. Indeed, both the Josephson and Giaever tunnelings were detected in the sintered compound with a nominal x = 0.25. In this compound, a re-entrant superconducting transition been observed resistively but not magnetically. It was also found that the electron density of states of the Al + 11.3at.%Si alloy is smaller than that of the bulk Al