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We present here the influence of different surface terminations on the electronic, optical, and photocatalytic properties of trans and cis BaTaO2N using density functional theory calculations. For each surface, we consider two complementary terminations exposed with Ba and Ta atoms, respectively. The calculated surface energies suggest that (001) and (100) are more stable than other low-index surfaces. Work functions are distinct for various surface terminations, which can be attributed to the atomic displacements in different directions and degrees after relaxation. We propose that the transferring direction of the photogenerated carriers in BaTaO2N-based heterostructures could be controlled by obtaining the preferred surface termination. The simulated absorption spectra suggest that both trans and cis BaTaO2N exhibit optical anisotropy, which could result from the difference in relaxed crystal parameters along different directions. Dissociative water adsorption on both the (001) and (100) terminations is thermodynamically favorable. The hydrogen evolution reaction (HER) is easier to occur on the terminations exposed with Ta, O, and N simultaneously. The computed overpotentials of oxygen evolution reaction (OER) for trans-(001)-BaO, cis-(001)-TaON, cis-(001)-BaO, and cis-(100)-Ta2O3N are in good agreement with the experimental results. These findings provide important insights into the rational design of (001)- and (100)-oriented BaTaO2N samples for enhanced photocatalytic activity. [ABSTRACT FROM AUTHOR]

Codoping with cations and anions is found to be an effective approach to tailor the electronic structures of semiconductor-based photocatalysts. In this work, a systematic hybrid density functional study has been carried out for BaTiO3 with a wide bandgap, codoped with TM and X (TM = V, Nb, Ta, Mo and W, X = N and C), with the objective of improving its photocatalytic activity for water splitting under visible light irradiation. Oxygen-rich conditions are found to be more favorable for the synthesis of the (TM + X)-codoped materials, and under these conditions, the formation energy for the codoped BaTiO3 is even lower than that of the TM-monodoped system. A smaller deformation of the BaTiO3 crystal structure corresponds to a more favorable formation of (TM + X)-codoped systems. Passivated codoping is found to be advantageous because it effectively reduces the band gap without encountering any localized impurity states observed in the related monodoped systems. The band alignments for all the codoped systems are well positioned for the feasibility of both photooxidation and photoreduction of water. It is found that there are seven investigated systems with bandgaps smaller than 3 eV. Among them, passivated codoped systems including Mo and W have been found to be the most effective for narrowing the bandgap (Eg is in the range of 1.55–2.16 eV), increasing the mobilities of photoinduced carriers and improving the photocatalytic activity of BaTiO3 under visible light. These materials are promising photocatalysts for overall water splitting under visible-light irradiation and further experimental investigations are highly demanded to explore their potential applications in the photocatalytic field. [ABSTRACT FROM AUTHOR]