Influence of Oxygen Vacancies on the Structure of BiVO4

Nicklas Österbacka,Julia Wiktor

doi:10.1021/acs.jpcc.0c08751

Nicklas Österbacka, Julia Wiktor

Open Access

https://doi.org/10.1021/acs.jpcc.0c08751

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Abstract

We study oxygen vacancies in the tetragonal scheelite phase of bismuth vanadate and identify stable oxygen-deficient structures. Upon subjecting these to variable-cell optimization, we find that oxygen vacancies give rise to significant structural distortions, the degree of which exhibits a vacancy concentration dependence. Furthermore, we show that these distortions give rise to splitting of powder X-ray diffraction peaks, yielding patterns similar to that of the monoclinic scheelite phase, and that these effects are also present at finite temperatures. Our results highlight the need for characterization methods beyond X-ray diffraction for identifying the phase of synthesized bismuth vanadate samples and the importance of oxygen partial pressure control during synthesis.

Highlights

Bismuth vanadate, BiVO4, is a promising candidate material for photoelectrochemical (PEC) water splitting due to the moderate band gap of around 2.4 eV and favorable band alignment of its monoclinic scheelite phase with the water oxidation potential.[1]
As demonstrated by Seo et al.,[21] the oxygen vacancy in bismuth vanadate exists in numerous configurations, differing by the coordination of V atoms around the defect and by where the two excess electrons are localized
Our results indicate that Powder Xray diffraction (PXRD) is insufficient to unambiguously determine whether the phase of synthesized BiVO4 samples is monoclinic scheelite unless a significant concentration of oxygen vacancies is ruled out

Summary

■ INTRODUCTION

BiVO4, is a promising candidate material for photoelectrochemical (PEC) water splitting due to the moderate band gap of around 2.4 eV and favorable band alignment of its monoclinic scheelite phase with the water oxidation potential.[1]. The degree of peak splitting at 35, 46, and 50° increases with vacancy concentration, with 3.2% ratio being most pronounced of the optimized systems considered here It has been suggested by Kim and Lee that lesser splitting of the peak around 19° may indicate a mixture of ts and ms phases.[60] The spectra of oxygen-deficient structures here exhibit a weaker splitting of that peak than the experimental ms structure, demonstrating that this phenomenon may arise due to cell distortions induced by oxygen vacancies as well. This technique, unlike the others discussed here, has the additional benefit of allowing for the detection of oxygen vacancies in the bulk

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES