Ab Initio Insights into Charge Localization in Bismuth Oxyhalides BiOX (X = F, Cl, Br, I)

Abstract

Developing efficient photocatalysts for clean energy generation is crucial to achieving net-zero emissions. To this end, we investigate the behavior of photoexcited charges in bismuth oxyhalides BiOX (X = F, Cl, Br, and I), a family of inexpensive and promising photocatalysts. To model the localization of excess electrons and holes, we use hybrid density functional theory PBE0(α). Our results indicate that electron polarons are unstable in these materials. Concurrently, we find that hole localization is favorable, and we identify two different possible configurations in which polarons are formed. One consists of two dimerized halogen atoms (VK center) and is preferentially formed in BiOBr and BiOI with binding energies that amount to −0.26 and −0.21 eV, respectively. The other corresponds to localization on a single Bi site and the surrounding oxygen and halogen atoms (BiXO). This form of polaron is favorable in BiOF and BiOCl with binding energies that amount to −0.35 and −0.23 eV, respectively. These findings highlight the behavior of photogenerated carriers and may open up avenues for future investigations on carrier transport in bismuth oxyhalides.

Probing the Polaronic Landscape in Bi4TaO8X Perovskite Oxyhalides Photocatalysts

“…It is worth noting that the hole localization centered on a single oxygen localization found here was not found to be stable in BiOCl and BiOBr, despite the similarities in the structural features of [Bi 2 O 2 ] block in both material families . The last localization mode worth exploring is around a single Bi site, similar to the ones previously reported in BiVO 4 and oxyhalides (BiOCl and BiOBr). ,, In this polaron configuration in BiVO 4 , the lengths of some Bi–O bonds increase and others decrease. , In the case of oxyhalides (BiOBr and BiOCl), the hole polaron at the Bi site causes a symmetrical contraction of both Bi–O bonds and Bi–X bonds . Considering that there are two distinct Bi sites in the perovskite oxyhalide structure, the Bi P site at the interface with [MO 4 ] block and the Bi X site within [Bi 2 O 2 ] block (see Figure ), we apply structural distortions around both of them.…”

“…It is worth noting that the hole localization centered on a single oxygen localization found here was not found to be stable in BiOCl and BiOBr, despite the similarities in the structural features of [Bi 2 O 2 ] block in both material families. 11 The last localization mode worth exploring is around a single Bi site, similar to the ones previously reported in BiVO 4 and oxyhalides (BiOCl and BiOBr). 11,25,26 In this polaron configuration in BiVO 4 , the lengths of some Bi−O bonds increase and others decrease.…”

“…This implies that, despite the fact that X−X distances in Bi 4 TaO 8 X are comparable with the intralayer ones in BiOX, the V k centers are unstable in perovskite oxyhalides, in contrast to what we observed previously in BiOCl and BiOBr. 11 This difference in the behavior of holes can be explained by the fact that the VBM of Bi 4 TaO 8 X primarily consists of O 2p instead of Cl 3p or Br 4p like in the case in BiOX. Consequently, we explore the two blocks [MO 4 ] and [Bi 2 O 2 ] that contain oxygen atoms to allow for polaronic configurations involving oxygen.…”

“…25,26 In the case of oxyhalides (BiOBr and BiOCl), the hole polaron at the Bi site causes a symmetrical contraction of both Bi−O bonds and Bi−X bonds. 11 Considering that there are two distinct Bi sites in the perovskite oxyhalide structure, the Bi P site at the interface with [MO 4 ] block and the Bi X site within [Bi 2 O 2 ] block (see Figure 1), we apply structural distortions around both of them. We first investigate the Bi X site by shortening the Bi−O/X bonds and introducing a hole into the system.…”

Band-structure tunability via the modulation of excitons in semiconductor nanostructures: manifestation in photocatalytic fuel generation

“…5a displays the layered BiOX characterized by [Bi 2 O 2 ] 2+ and [X 2 ] layers interacting via weak van der Waals forces. 81 BiOX is composed of a tetragonal matlockite crystalline structure and with an increase in the atomic number of X, the absorption range of incident photons shifted from UV light (BiOCl) to red light (BiOI). Remarkably, the band gap gradually decreased with an increase in atomic number, as shown in Fig.…”