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The conductivity and Seebeck coefficient of the perovskite‐type oxides La1−xSrxCoO3−δ false(x=0–0.7false) were measured in 10–5−1 normalatm O2 gas at temperatures 25°–1000°C. The results are discussed in relation to the lattice‐parameter and oxygen non‐stoichiometry. Close relationships were found between the temperature dependence of the conductivity and the rhombohedral angle, α. For La1−xSrxCoO3−δ with α<60.3°–60.4° ( LaCoO3−δ above 800°C and La1−xSrxCoO3−δ with x>0.5 at room temperature), the conductivity decreases with temperature, suggesting metallic conduction. For La1−xSrxCoO3−δ with α>60.4° , the conductivity increases with temperature like semiconductors. In the oxides with metallic conduction, the conductivity was found to decrease with increase in the oxygen vacancy concentration. Because the conduction band is composed of the Co‐O‐Co network, it is considered that the band is distributed by the formation of oxygen vacancies and becomes narrower, resulting in the decrease in conductivity.

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A point-contact Josephson junction between a bulk Ba-Y-Cu-O compound (T c -90 K) and a Nb needle has been made. The I-V characteristics under microwave radiation show Shapiro steps, confirming the Josephson nature of the formed contact. Spin-singlet superconductivity in the Ba-Y-Cu-O system is implied from the voltage of the steps. The temperature dependence of the critical currents suggests that the Josephson junction if formed between Nb and another material with much higher T c . Internal Josephson structure within the bulk ceramics is not found in the Ba-Y-Cu-O system. PACS numbers: 74.50.+r, 74.70.YaRecently a series of high-7V ceramic superconductors have been discovered, 1 triggered initially by the historic finding in the Ba-La-Cu-O system. 2 Among those superconducting oxides, the Ba-Y-Cu-O compound emerged as the first material to show a reproducible T c higher than liquid-nitrogen temperature, a technological, as well as psychological, milestone temperature. As for the origin of the superconductivity in these high-T c superconductors, which are categorized as ceramic superconductors, several exotic mechanisms have been suggested such as interfacial superconductivity, 3 resonatingvalence-bond theory, 4 and also phonon-mediated superconductivity. 5 Experimentally, the superconductivity in these ceramics has been confirmed through resistance measurements and ac and dc diamagnetism measurements. The only known physical mechanism which can produce the large dc diamagnetism is superconductivity. Alongside the zero-resistance state and the Meissner effect, the existence of macroscopic quantum phenomena signifies the central ideas of the superconductivity. The Josephson junction is the celebrated quantumphase-sensitive detector capable of proving the wave nature of superconductive system. For instance, the difference in the macroscopic quantum phases of the electron pairs across the Josephson junction (phase difference ) is related to the amount of the supercurrent flowing through the junction, and the rate of change in the phase difference, d