Defect physics investigations in bulk NaBiO3 photocatalysts via Heyd–Scuseria–Ernzerhof hybrid density functional theory calculations

Abstract

This study employs Heyd–Scuseria–Ernzerhof hybrid density functional theory calculations to thoroughly investigate the n-type and p-type conductivity mechanisms of NaBiO₃ photocatalysts. The results reveal that the intrinsic interstitial defect Na¹⁺_i is dominant under most growth conditions because of its lower formation energy. It is an excellent donor because of its shallower charge transition level. This makes it easily reach and even exceed the significant concentration of 10²¹ cm⁻³ with Na chemical potential regulation. Thus, in most circumstances, the intrinsic n-type conductivity of NaBiO₃ found in experiments should primarily originate from the contribution of the interstitial defect Na¹⁺_i. The anti-site defect Bi²⁺_Na also contributes to the unintentional n-type conductivity behavior. Especially under Na-poor and Bi-rich growth conditions, Bi²⁺_Na becomes the dominant defect and is most responsible for the intrinsic n-type conductivity. The two major intrinsic defects, including Na¹⁺_i and Bi²⁺_Na defects, can act as the photocatalytic reaction active sites or as a hole capture center (Bi²⁺_Na) rather than as the recombination centers of the photo-generated electrons and holes in NaBiO₃. On the other hand, based on thermodynamic simulation, the study examines the impacts of n-type and p-type doping at a fixed donor D⁺ or acceptor A⁻ concentration on the conductive properties of NaBiO₃ under different chemical potential conditions. It is indicated that p-type doping can convert the intrinsic n-type NaBiO₃ into a p-type semiconductor only under non-thermal equilibrium growth conditions (quenching method). In contrast, n-type doping can easily enhance its n-type carrier concentration. Our results can guide optimizing the growth conditions to achieve high donor doping and high photocatalytic performance in NaBiO₃ or NaBiO₃-based materials.