Effect of oxygen vacancies on carrier localization in BaPb 1− xBi xO 3

Abstract

Resistivities and Hall coefficients have been measured between 4.2 and 300 K for superconducting BaPb 1− x Bi x O 3 single crystal thin films containing various amount of oxygen vacancies. The results show that the oxygen vacancies cause strong carrier localization - a bipolaron formation at the Bi ions. The density of carriers suffering this localization increases with the amount of the oxygen vacancies. When the fraction of localized carriers exceeds a critical value, Anderson localization follows owing to the random potential field caused by the ionized localization centers. This model clearly explains the abrupt T c decrease and the metal-semiconductor transition in this system near x = 0.3. Furthermore, it is also implies that T c will become higher with the increase of Bi content even at x > 0.3 if the oxygen vacancies could be reduced sufficiently.