Effect of oxygen nonstoichiometry on electrical conduction property of BaBiO3−δ

In order to clarify the effect of oxide ion vacancy on electronic structure of BaBiO3−δ, electrical conduction property at high temperature under various oxygen partial pressures, P(O2), was investigated. At 775 °C, in dependence of electrical conductivity on log P(O2) three phases were observed, showing agreement with oxygen nonstoichiometry data measured with thermogravimetry. Under log P(O2) higher than −1.75, n-type semiconducting property was observed which could be attributed to charge density wave originating from two kinds of Bi sites in crystal structure. In log P(O2) region between −1.75 and −2.45, electrical conductivity almost independent of log P(O2) was observed. This suggested semi-metallic electronic structure with itinerant electron which could originate from single Bi site in BaBiO3−δ with ideal perovskite structure clarified by neutron diffraction. Below log P(O2) of −2.45, abrupt decrease of electrical conductivity was observed, suggesting localization of electron in Bi orbital, which could also be speculated from low symmetry around Bi site in BaBiO2.5.