Oxygen deficiency, crystal system and conduction behavior of BaPb0.75Bi0.25O3-δ

Abstract

The variation of crystal system and conduction behavior of perovskite superconductor, BaPb 0.75 Bi 0.25 O 3-δ , with oxygen deficiency was studied. The crystal system of BaPb 0.75 Bi 0.25 O 3-δ changed from orthorhombic through tetragonal to pseudo-cubic as δ increases. The superconducting transition was observed in the specimens with the orthorhombic phase. Oxygen-deficient specimens with tetragonal or pseudo-cubic symmetry did not show a superconducting transition. The increase in electrical resistivity was also observed with an increase in δ, which suggested decrease of electron carrier mobility with the increase in δ. This effect of oxygen deficiency on conduction behavior of BaPb 0.75 Bi 0.25 O 3-δ showed contrast with those of the superconducting cuprates, in which carrier concentration is affected instead of carrier mobility. The difference in the effects of oxygen deficiency on conduction behavior could be attributed to the difference of crystal structure between BaPb 0.75 Bi 0.25 O 3-δ and superconducting cuprates.