Carrier and oxygen vacancy engineering of aliovalent ion modified BiFeO3 and their gas sensing properties

Even if the application of semiconducting metal oxide-based gas sensors has flourished over decades, the basic understanding of how sensing characteristics are regulated remains elusive. In particular, the role of oxygen vacancy in sensing properties of p-type semiconductors has not been well investigated thus far. In this work, pristine and aliovalent ion-doped p-type multiferroic BiFeO3 sensors were prepared by a sol-gel method, and the effect of doping on the carrier type, oxygen vacancy concentration, and gas sensing properties was studied. The gas response of BiFeO3 increased 48 % upon 1 % Ca doping and decreased 50 % when 1 % Ti was doped in. This is because Ca-doped BiFeO3 increases the concentration of carriers (hole) and oxygen vacancies, while Ti-doped BiFeO3 does the opposite. In addition, the conduction characteristics of BiFeO3 were transformed from p-type to n-type upon further substitution of Fe3+ by Ti4+. This work proves that aliovalent ion doping can regulate the concentration and type of carriers in materials, as well as the control of gas sensing properties, thus shedding a light on the design of high-performance p-type semiconductors.