XYO3 (X = K, Na; Y = Nb, Ta) based superlattices for photocatalysis

The photocatalytic activities of XYO3 (X = K, Na; Y = Ta, Nb) and XYO3/X1Y1O3 (X, X1 = K, Na; Y, Y1 = Ta, Nb) systems are investigated by using hybrid density functional. All the XYO3 and XYO3/X1Y1O3 systems are indirect band gap semiconductors, and the band gap of KNbO3/KTaO3 is smaller than those of KNbO3 and KTaO3, while the band gaps of KNbO3/NaNbO3, KNbO3/NaTaO3, KTaO3/NaNbO3, KTaO3/NaTaO3, and NaNbO3/NaTaO3 are respectively between the band gaps of these two crystals which make up these superlattices. The electronic structure of KNbO3/NaTaO3 is the same as that of KTaO3/NaNbO3 since both have the same component and similar crystal structure. The band edges of all the considered superlattices are thermodynamically allowed for the water reduction and oxidation processes, and therefore, they could be used for photocatalytic water splitting. Band structures for (i) KNbO3/KTaO3, (ii) KNbO3/NaNbO3, (iii) KNbO3/NaTaO3, (iv) KTaO3/NaNbO3, (v) KTaO3/NaTaO3, and (vi) NaNbO3/NaTaO3 superlattices. The horizontal dashed lines represent the Fermi levels.