Metal-insulator transition and superconductivity in Sr- and La-substitutedBaPb1-xBixO3

Compositional boundaries of the metal-insulator transition (MIT) in Sr- and La-substituted BaPb1-xBixO3 (BPBO) were determined by de susceptibility, e lectrical resistivity and thermoelectric power (TEP) measurements. By the 2 0% substitution of Sr for Ba, a Bi compositional range for metallic (superc onducting) phase considerably extended to the Bi-rich region (x approximate to 0.5), though BPBO exhibited metal (superconductivity) only below x = 0. 3. On the other hand, by the 10% La substitution, a Bi range for metal (sup erconductivity) slightly decreased to the Bi-poor region (x approximate to 0.25). Transport properties indicated that the MIT takes place at the latti ce parameter a(p) approximate to 4.29 Angstrom, irrespective of the substit ution elements. This suggests that the cell size determining the Bi-O orbit al overlap and/or a magnitude of the band split, is one of the essential fa ctors of the MIT in BPBO. (C) 1999 Elsevier Science B.V. All rights reserve d.