title: A soft X-ray spectroscopic perspective of electron localization and transport in tungsten doped bismuth vanadate single crystals.
abstract: Doped BiVO4is a promising photoelectrochemical water splitting anode, whose activity is hampered by poor charge transport. Here we use a set of X-ray spectroscopic methods to probe the origin and nature of localized electron states in W:BiVO4. Furthermore, using the polarized nature of the X-rays, we probe variations in the electronic structure along the crystal axes. In this manner, we reveal aspects of the electronic structure related to electron localization and observations consistent with conductivity anisotropy between the ab-plane and c-axis. We verify that tungsten substitutes as W6+for V5+in BiVO4. This is shown to result in the presence of inter-band gap states related to electrons at V4+sites of e symmetry. The energetic position of the states in the band gap suggest that they are highly localized and may act as recombination centres. Polarization dependent X-ray absorption spectra reveal anisotropy in the electronic structure between the ab-plane and c-axis. Results show the superior hybridization between V 3d and O 2p states, higher V wavefunction overlap and broader conduction bands in the ab-plane than in the c-axis. These insights into the electronic structure are discussed in the context of existing experimental and theoretical reports regarding charge transport in BiVO4.
authors.affiliation: School of Chemical Sciences and Centre for Green Chemical Sciences, The University of Auckland, Auckland 1142, New Zealand. vjov001@aucklanduni.ac.nz and The MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, Wellington 6140, New Zealand.
authors.forename: Vedran
authors.initials: V
authors.lastname: Jovic
authors.affiliation: McKetta Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Alexander J E
authors.initials: AJ
authors.lastname: Rettie
authors.affiliation: Department of Physics, Boston University, Boston, MA 02215, USA.
authors.forename: Vijay R
authors.initials: VR
authors.lastname: Singh
authors.affiliation: Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Jianshi
authors.initials: J
authors.lastname: Zhou
authors.affiliation: Department of Physics, Boston University, Boston, MA 02215, USA.
authors.forename: Bethany
authors.initials: B
authors.lastname: Lamoureux
authors.affiliation: McKetta Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712, USA and Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: C
authors.identifier: http://orcid.org/0000-0003-1030-4801
authors.initials: C
authors.lastname: Buddie Mullins
authors.affiliation: Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Bluhm
authors.affiliation: Department of Physics, Boston University, Boston, MA 02215, USA and School of Physics, H.H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK.
authors.forename: Jude
authors.initials: J
authors.lastname: Laverock
authors.affiliation: School of Chemical Sciences and Centre for Green Chemical Sciences, The University of Auckland, Auckland 1142, New Zealand. vjov001@aucklanduni.ac.nz and The MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, Wellington 6140, New Zealand and Department of Physics, Boston University, Boston, MA 02215, USA.
authors.forename: Kevin E
authors.initials: KE
authors.lastname: Smith