High pressure synthesis and superconductivity of Ba1-xKxBiO3 (0.35 < x < 1)

The whole region of superconductivity in the Ba(1-x)KBio(3) (BKBO) system (0.35 < x < 1) has been investigated by synthesizing the samples with the high pressure and high temperature technique. As the K doping ratio (x) increases, the superconducting transition temperature (T-c) of the BKBO system decreases from 30.4 K for x = 0.37 to very low diamagnetic signal below 3 K for x = 0.74. The synthesis of the samples without including any bariums in the starting composition (x = 1) resulted in different T-c and lattice parameters from sample to sample with partial substitutions of Bi at the K site in final products. With detailed synthesis information of the BKBO samples which varies with x, the evolution of T-c by doping in the cubic BKBO system is compared with other superconducting bismuthates and discussed on a basis of its electronic band structure. (C) 2002 Elsevier Science B.V. All rights reserved.