Effect of intentional chemical doping on crystallographic and electric properties of the pyrochlore Bi2Sn2O7

The development of p-type oxide semiconductors is challenging owing to the localized nature of the valence band maximum (VBM), which primarily comprises O 2p orbitals. Although some Sn2+-based pyrochlore-type oxides (A2B2O7) with VBMs comprising spatially spread Sn 5s orbitals show p-type semiconducting properties, these properties cannot be tuned by an intentional chemical doping owing to the instability of their valence states. Herein, the influence of chemical doping on the crystal structure and electrical properties of Bi2Sn2O7, whose VBM is composed of valence-stable ions with Bi 6s orbitals, in the VBM is investigated. X-ray absorption spectroscopy reveals that In3+ is doped substitutionally at the Sn4+ site. Although the doped In3+ ions are expected to act as acceptors, their electrical properties always show n-type character. Simultaneously, extended X-ray absorption fine structure reveals the formation of oxygen vacancies in BiOBi bonds contributing to the VBM, whereas negligible changes are observed in the SnO6 octahedra, suggesting that the generated holes are electrically compensated by electrons because of the oxygen vacancies. P-type electric properties can be observed under oxidizing conditions, providing a critical design concept for the realization of hole conduction in acceptor-doped Bi2Sn2O7.