Theoretical Investigations on the n-Type and p-Type Conductivity Mechanisms in BiTaO4 Photocatalysts through Intrinsic Point Defects and Group IIA and Group VIB Element Doping.

Abstract

The n-type and p-type conductivity mechanisms from intrinsic defects and Group IIA and Group VIB element doping in the photocatalyst BiTaO₄ are systematically investigated by employing hybrid density functional calculations. The results reveal that vacancies V_Bi, V_Ta, V_O, and antisite Ta_Bi are the predominant defects, depending on growth conditions. Bi-rich, appropriate Ta-rich, and O-poor conditions can promote BiTaO₄ to form n-type conductivity due to the presence of the Ta_Bi donor defect and its easier ionization. This explains the experimental n-type conductivity character well. Meanwhile, under O-rich, Bi-poor, and Ta-poor conditions, BiTaO₄ exhibits superior p-type conductivity by forming the excellent acceptor defects V_Bi and V_Ta. Moreover, the intrinsic p-type conductivity can be further strengthened via the introductions of the substitutional doping of M_Bi (M = Mg, Ca, Sr, and Ba) under the Bi-poor, Ta-poor, and O-rich conditions, where the O vacancies should be induced and Sr is the best candidate. On the other hand, Group VIB element (Cr, Mo, and W) doping can improve intrinsic n-type conductivity under Bi-rich, appropriate Ta-rich, and O-poor conditions. W is the best candidate. These findings provide a comprehensive understanding of defect physics in BiTaO₄ and offer insights into optimizing its photocatalytic performance through targeted defect engineering and impurity doping.