EFFECT OF AL ON ELECTRIC-CONDUCTIVITY AND SUPERCONDUCTIVITY OF NB-SI-AL-O CERAMIC

Metal-insulator transition and superconductivity with changing Al comp osition were observed in the Nb-Si-Al-O system. Semiconductor-like cha racteristic and normal conductive characteristic were observed for Al < 40% and Al > 50% respectively. Superconductive compositions are dist ributed around the boundary between those two types of conductivity, s uch as Nb(x)SiAl(alpha-x)O(z)((alpha, x) = (1.5, 0.7), (2.0, 0.8), (3. 0, 0.7 - 1.4)). The superconductivity was confirmed by resistive trans itions and diamagnetic transitions. The superconductors in this study have T(c) = 10.0 - 11.5 K with resistive transitions, and the amplitud es of the diamagnetism reach 30 - 58% of that of pure Nb powder. X-ray diffraction patterns of any other superconducting Nb-systems such as Nb, Nb3Al, Nb3Si, NbN, and NbC, have not been observed in Nb-Si-Al-O.