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Hole transport in pure and doped hematite
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10.1063/1.4730634
/content/aip/journal/jap/112/1/10.1063/1.4730634
http://aip.metastore.ingenta.com/content/aip/journal/jap/112/1/10.1063/1.4730634

Figures

Image of FIG. 1.
FIG. 1.

Illustrations of the six clusters used to study hole transfer: (a) Fe2O10 13−, (b) Fe4O16 19−, (c) Fe6O24 29−, (d) Fe8O30 35−, (e) Fe6O24 29−, and (f) Fe7O26 30−. The capping effective core potentials and point charge arrays are not shown. Fe ions are in grey. O ions are in red. This color scheme is followed throughout. The “+” and “−” to the left of each cluster indicate the signs of spins of Fe 3d electrons within the corresponding Fe layer. The O anions considered for hole transfer are in black circles and are labeled “O1” and “O2” in the figures. The Fe cations in green circles indicate the different cation substitution locations studied. The dashed lines in (d) refer to layers of Fe-O bonds, with labeling numbers next to the lines.

Image of FIG. 2.
FIG. 2.

PE curves along linear nuclear coordinates for hole transfer within (a) an O-edge pair in the Fe6O24 29 cluster, (b) an O-long pair, and (c) an O-short pair (see Figure 1 ). The PE curve on the left is for the hole on O1 (black triangles) and the PE curve on the right is for the hole on O2 (white triangles). The zero of energy is referenced to x = 0 of the PE curve labeled with “▴.” The black triangles linked by smooth curves are actual calculation data points. The isolated blue triangles indicate cases where the wavefunction relaxed to lower energy states on the other PE curve below and the positions of the blue triangles are determined from second order polynomial fitting of the corresponding PE curve. See Table I for spin states of each cluster.

Image of FIG. 3.
FIG. 3.

Absolute values (top panel) and percentage changes (bottom panel) of Fe-O bond lengths in the Fe8O30 35− cluster before and after introducing a hole on O1 (Ms = 1/2, see Table I ). See Figure 1(d) for illustration of the Fe-O bond index on the x-axis.

Image of FIG. 4.
FIG. 4.

Density difference isosurface plots for three cluster models: (a) Fe6O24 29− (Ms = −11/2), (b) Fe6O24 29− (Ms = 1/2), and (c) Fe7O26 30− (Ms = 3). The electron densities are taken from the crossing point geometry. The density difference is calculated as the electron density from the left PEcurve (hole on O1) minus the electron density from the right PE curve(hole on O2). The positive isosurface is colored pink and the negativeisosurface is colored purple. A contour value of 0.20 electrons/Å3 is used.

Image of FIG. 5.
FIG. 5.

PE curves along linear nuclear coordinates for hole transfer within the O-edge pair with single cation substitutions with different dopants or at different positions. See captions of Figure 2 for detailed conventions used for the plots, Figure 1(b) for illustrations of the dopant positions, and Table II for details about cluster spin states.

Image of FIG. 6.
FIG. 6.

Density difference isosurface plots for the Fe4O16 19− cluster with single cation substitution by Cu (blue sphere in (a) and (b)) or Mn (brown sphere in (c) and (d)). The electron densities are taken from the crossing point geometry. The density difference is calculated as the electron density with one hole (Cu2+@mid in Ms = −5/2, Cu2+@down in Ms = 5/2, Mn3+@mid in Ms = −1, and Mn3+@down in Ms = 1) subtracting the electron density without any hole. See captions of Figure 4 for color conventions and contour values used.

Image of FIG. 7.
FIG. 7.

M-O bond lengths (M = Fe3+, Mg2+, Ni2+, Cu2+, Mn2+, or Mn3+) in the Fe4O16 19− cluster without cation substitutions (Fe) or with single cation substitutions (here the O anion with the unpaired electron is in the Ms = −1/2 state for M@mid and in the Ms = 1/2 state for M@down; see Table II for the corresponding spin states). The geometries are optimized with the hole on O1 ((a) and (c)) or O2 ((b) and (d)). See Figure 1(b) for illustrations of the O index and the positions of M.

Image of FIG. 8.
FIG. 8.

PE curves along linear nuclear coordinates for hole transfer between O anions and Mn2+@mid in the Fe4O16 19− cluster. See captions of Figure 2 for detailed conventions used for the plots and Figure 1(b) for illustrations of the dopant positions.

Image of FIG. 9.
FIG. 9.

Density difference isosurface plots for the Fe4O16 19− cluster with single cation substitution by Mn2+. The electron densities are taken from the crossing point geometry. The density difference is calculated as the electron density with one hole (on O1/O2 or Mn) minus the electron density without a hole. See captions of Figure 4 for color conventions and contour values used.

Image of FIG. 10.
FIG. 10.

PE curves along linear nuclear coordinates for hole transfer within two different O pairs (O-edge and O-long) with single Mg substitutions in hematite clusters at different positions. See captions of Figure 2 for detailed conventions used for the plots, Figures 1(b) and 1(d) for illustrations of the dopant positions and Table III for details of cluster spin states.

Tables

Generic image for table
Table I.

Spin states for the six clusters in Figure 1 . The formation of a hole gives rise to an unpaired O 2p electron, the spin of which can be either +1/2 or −1/2. Two possible net spin states are listed under the column with one hole formed in the clusters.

Generic image for table
Table II.

Spin states for the doped Fe4O16 19− cluster in Figure 1(b) . The spins of the transition metal dopants are set to follow the same sign as those of the substituted Fe (“+” for M@mid or “−” for M@down). See Figure 1(b) for dopant positions.

Generic image for table
Table III.

Spin states for the Mg-doped O-edge and O-long Fe6O24 29− clusters. See Figures 1(c) and 1(e) for illustrations of clusters as well as dopant positions.

Generic image for table
Table IV.

Diabatic activation energies ΔG* and reorganization energies λ (in eV) for hole transfer within different oxygen ion pairs in pure hematite. Because the O-edge pair is symmetrically equivalent, the ΔG* and λ are the same for “O1 → O2” and “O1 ← O2.” All results, except those under “CASSCF” for Fe2O10 13−, are from UHF calculations. See Figure 1 for illustrations of the clusters and Table I for details of cluster spin states.

Generic image for table
Table V.

Diabatic activation energies ΔG* and reorganization energies λ (in eV) for hole transfer within O-edge pairs in the Fe4O16 19− cluster with a single cation substitution. See Figure 1(b) for positions of substitutions and Table II for details of cluster spin states.

Generic image for table
Table VI.

Diabatic activation energies ΔG* and reorganization energies λ (in eV) for hole transfer between O anions and Mn in the Fe4O16 19− cluster with a single cation substitution of Mn at the “mid” position. See Figure 1(b) for positions of substitutions.

Generic image for table
Table VII.

Diabatic activation energies ΔG* and reorganization energies λ (in eV) for hole transfer within different O pairs with single Mg substitution at different positions in hematite clusters. See Figures 1(c) and 1(e) for illustrations of the dopant positions and Table III for details of cluster spin states.

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/content/aip/journal/jap/112/1/10.1063/1.4730634
2012-07-02
2014-04-23
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Hole transport in pure and doped hematite
http://aip.metastore.ingenta.com/content/aip/journal/jap/112/1/10.1063/1.4730634
10.1063/1.4730634
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