Structural phase-dependent hole localization and transport in bismuth vanadate

Kyoung E. Kweon and Gyeong S. Hwang

Phys. Rev. B 87, 205202 – Published 9 May 2013

Abstract

We present theoretical evidence for the phase dependence of hole localization and transport in bismuth vanadate (BiVO $_{4}$ ). Our hybrid density-functional theory calculations predict that, in the tetragonal phase [tetragonal scheelite BiVO $_{4}$ ( $t s$ -BiVO $_{4}$ )], an excess hole tends to localize around a BiO $_{8}$ polyhedron with strong lattice distortion, whereas, in the monoclinic phase [monoclinic scheelite BiVO $_{4}$ ( $m s$ -BiVO $_{4}$ )], it spreads over many lattice sites. The phase-dependent behavior is likely related to the higher structural stability of $m s$ -BiVO $_{4}$ than $t s$ -BiVO $_{4}$ , which may suppress hole-induced lattice distortions. Our study also demonstrates that the relatively weakly localized hole in $m s$ -BiVO $_{4}$ undergoes faster diffusion compared to the case of $t s$ -BiVO $_{4}$ , irrespective of the fact that the degrees of localization and mobility vary depending on the choice of exchange-correlation functional. The mobility difference may provide an explanation for the enhanced photocatalytic activity of $m s$ -BiVO $_{4}$ over $t s$ -BiVO $_{4}$ for water oxidation, considering that the increased mobility would lead to an increase in the hole current to the catalyst surface.

Received 9 January 2013

DOI:https://doi.org/10.1103/PhysRevB.87.205202

Authors & Affiliations

Kyoung E. Kweon and Gyeong S. Hwang^*

Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, USA

^*Author to whom correspondence should be addressed: gshwang@che.utexas.edu

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 87, Iss. 20 — 15 May 2013

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a) Crystal structure representation of scheelite BiVO $_{4}$ with an indication of BiO $_{8}$ dodecahedra (in purple) and VO $_{4}$ tetrahedra (in gray) along with schematics of (b) symmetric BiO $_{8}$ dodecahedron in $t s$ -BiVO $_{4}$ and (c) distorted BiO $_{8}$ dodecahedron in $m s$ -BiVO $_{4}$ . The arrow [in (c)] indicates Bi atom displacement along the $c$ axis with respect to its corresponding position in $t s$ -BiVO $_{4}$ (as indicated by the dotted line). There are two ( $d_{1}$ and $d_{2}$ ) and four ( $d_{1}$ , $d_{2}$ , $d_{3}$ , and $d_{4}$ ) different kinds of Bi-O bond lengths in $t s$ -BiVO $_{4}$ and $m s$ -BiVO $_{4}$ , respectively; the $d$ values are listed in Table . Purple, silver, and red balls represent Bi, V, and O atoms, respectively.Reuse & Permissions
Figure 2
Electron density of states (DOS) projected onto Bi 6 $s$ (shaded in gray) and Bi 6 $p$ (red solid line) states in (a) $t s$ -BiVO $_{4}$ and (b) $m s$ -BiVO $_{4}$ . In the inset, the blue and green solid lines indicate O 2 $p$ and V 3 $d$ states, respectively. The energy zero is set at the Fermi level ( $E_{F}$ ), which is indicated by vertical dashed lines.Reuse & Permissions
Figure 3
(Left panels) BiO $_{8}$ dodecahedron configurations and (right panels) orbital projected DOS for (a) polaronic and (b) nonpolaronic hole states in $t s$ -BiVO $_{4}$ . The insets (in right panels) show the band-decomposed charge densities of corresponding hole states (indicated by arrows) with isosurface values of (a) 0.010 $e$ /Å $^{3}$ and (b) 0.002 $e$ /Å $^{3}$ ; here, only the Bi-O bonds of selected BiO $_{8}$ dodecahedra are shown (and the corresponding bond lengths are indicated in Å in the left panels). In the DOS plots, the black, red, green, and blue solid lines indicate Bi 6 $s$ , Bi 6 $p$ , V 3 $d$ , and O 2 $p$ states, respectively. Purple, silver, and red balls represent Bi, V, and O atoms, respectively. The energy zero is set at the Fermi level ( $E_{F}$ ), which is indicated by vertical dashed lines.Reuse & Permissions
Figure 4
(Left panels) BiO $_{8}$ dodecahedron configurations and (right panels) orbital projected DOS for (a) polaronic and (b) nonpolaronic hole states in $m s$ -BiVO $_{4}$ . The insets (in right panels) show the band-decomposed charge densities of corresponding hole states (indicated by arrows) with an isosurface value of 0.002 $e$ /Å $^{3}$ ; here, only the Bi-O bonds of selected BiO $_{8}$ dodecahedra are shown (and the corresponding bond lengths are indicated in Å in the left panels). In the DOS plots, the black, red, green, and blue solid lines indicate Bi 6 $s$ , Bi 6 $p$ , V 3 $d$ , and O 2 $p$ states, respectively. Purple, silver, and red balls represent Bi, V, and O atoms, respectively. The energy zero is set at the Fermi level ( $E_{F}$ ), which is indicated by vertical dashed lines.Reuse & Permissions
Figure 5
(a) Energy variation along the polaron migration path linearly interpolated between two minimum-energy configurations for $t s$ -BiVO $_{4}$ ; the transition state (TS) occurs midway between the initial state (IS) and the final (FS) state. While the excess hole localizes around a BiO $_{8}$ polyhedron, the small-polaron positions in the initial and final states are colored in dark purple. (b) Band-structure diagram for $m s$ -BiVO $_{4}$ ; the bands are plotted along the Σ and Δ directions as specified in the Brillouin zone.Reuse & Permissions

Physical Review B

covering condensed matter and materials physics