Influence of point defects on the performance of InVO 4 photoanodes

Abstract

The properties of thin film InVO 4 photoanodes for water splitting have been studied. Compact films of InVO 4 were prepared by spray pyrolysis and are found to be stable between pH 3 -11. Although the indirect bandgap is 3.2 eV, a modest amount of visible light absorption is observed. The origin of this absorption is attributed to the presence of deep donor states at ~0.7 eV below the conduction band. Shallow donors are absent in this material, in contrast to what is normally observed for metal oxides. The deep donor model explains the much stronger visible light absorption of powders compared to thin films, and is supported by photoluminescence data. The origin of the deep donors is attributed to deviations in the In:V ratio, and the corresponding defect-chemical reactions will be discussed.

High Temperature Structural, Dielectric, and Ion Conduction Properties of Orthorhombic InVO4

“…An insignificant deviation from stoichiometry of In to V can also give rise to appreciable concentration of oxygen vacancies in the lattice. The authors have confirmed the presence of such oxygen vacancies by photoluminescence studies . In addition, the structure of InVO 4 can be explained as distorted cubic close‐packed oxygen lattice with partially occupied octahedral and tetrahedral sites.…”

“…However, the O–V–O angles in all of them remain close to the normal tetrahedral angles. Such distortions often destabilize the lattice and thus the structure has a tendency for polymorphic transformation under temperature or pressure, as well as to form significant amounts of intrinsic point defects in the lattice . To understand further on these aspects and their correlation with the electrical properties, in situ high‐temperature XRD and high‐temperature ac ‐ impedance studies were carried out and results are explained subsequently.…”

“…Thus, the origin of conductivity in such materials arises from the electronic as well as ion mobilities. Recent studies of van de Krol et al . in the context of the photocatalytic properties of InVO 4 revealed a deep electron donor state due to the formation of In interstitial () and the corresponding amounts of vacancies at V () and oxygen () sites.…”

“…Both the stable orthorhombic and metastable monoclinic modifications of InVO 4 have octahedral InO 6 and tetrahedral VO 4 units as building blocks of crystal structure. Also both the structures have significant open spaces to facilitate intercalation of cations like lithium and to create intrinsic defect structures with cation or anion interstitials …”

“…Both FeVO 4 and CrVO 4 are reported to be n ‐type semiconductors . Hopping of the thermally activated electrons due to the variable valence states or oxygen ion vacancies originating from the feeble nonstoichiometry has been attributed to their electrical conduction . Also literatures indicate a polaron hopping conduction in FeVO 4 even without any valance fluctuation of Fe or V .…”