We report the anomalous superconductivity found in bismuthates with different compositions. In the Sr1-xKxBiO3(SKBO) compound the field-induced superconductivity is observed, which shows a striking suppression of the reentrant resistance at T < Tcby applying an external magnetic field (H) or increasing the electrical transport current (I). The magnetotransport measurements on several different samples reveal that the reentrant resistance behavior with H and I is related to the normal state transport properties. Disordered junction barriers between superconducting grains seem to be important for the observed anomalous reentrant resistance phenomena. In the Ba1-xKxBiO3system, the whole region of the superconducting cubic phase diagram from x = 0.4 up to x = 1 was investigated for the first time by using the high pressure and high temperature synthesis technique. The superconducting temperature (Tc) of Ba1-xKxBiO3(BKBO) samples shows a parabolic decrease of Tcfrom the well-known Ba0.63K0.37BiO3composition with Tc= 30.4 K to Ba0.24K0.76BiO3with very low diamagnetic signal at nearly 3 K. However, we found that further increasing x gives an increase of Tcup to 9 K for x = 1. Possible physical origins of the field-induced superconductivity in SKBO and the anomalous superconducting region in high potassium concentration (x > 0.8) BKBO are discussed. © 2001 Elsevier Science B.V. All rights reserved.
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