Effects of La- and Pr-Substitution on the Structure and Superconductivity of Ba0.6K0.4BiO3

Two compositional series based on Ba0.6-yLayK0.4BiO3 and Ba0.6-zPrzK0.4BiO3, with y and z being 0, 0.025, 0.05, 0.1, 0.2, 0.3, 0.4, were synthesized using a molten salt method. X-ray powder diffraction data reveal that the initially undoped cubic crystal symmetry expands slightly to orthorhombic with Pr substitution but not with La substitution. A linearly reduction of the pseudo-lattice parameter following ap=4.28257–0.02469y (0.025≤y≤0.4) can be observed in Ba0.6-yLayK0.4BiO3. A systematic decrease of the transition temperature, Tc, is clarified by magnetic measurements and the superconductivity is finally vanished at y, z = 0.2 owing to the distortion of the crystal structure and the disproportionations of bismuth valence.