Structure and electrical properties of superconducting BaPb_1-xBi_xO₃

Abstract

The study of the crystal structure and composition of BaPb_1-xBi_xO₃ (BPB) provides important information for understanding electrical transport mechanisms. Two kinds of samples, tetragonal and orthorhombic, have been fabricated under different crystal growth conditions in the region below x = 0.5. Both kinds of crystals are superconducting at x < 0.35, although their transition temperatures differ from one another. An orthorhombic sample with x = 0.25 changes to a cubic phase above 620 K. Moreover, samples with x < 0.4 change, to a monoclinic phase at low temperatures, but the other samples remain orthorhombic above 4 K. On the other hand, a tetragonal sample with x = 0.25 changes to cubic above 670 K.

Electrical transport in BPB is strongly influenced by electron localization due to oxygen vacancies and Bi ions. In addition, oxygen deficiency is considerably large above x = 0.35. The composition-induced metal-semiconductor transition at x = 0.35 will be decisively influenced by such electron localization.

Key Words:

• superconducting oxides
• BaPb_1-xBi_xO₃ structural phase transition
• oxygen vacancies