Effect of cation arrangement on the electronic structures of the perovskite solid solutions ${(\mathrm{SrTiO}}_3\left){}_{1-x}{(\mathrm{LaCrO}}_3\right){}_x$ from first principles

The electronic structures of ${[\mathrm{SrTiO}}_3\left]{}_{1-x}{[\mathrm{LaCrO}}_3\right]{}_x$ perovskite solid solutions are studied using hybrid density functional calculations to investigate their potential photocatalytic activity. The introduction of ${\mathrm{Cr}}^{3+}$ into ${\mathrm{SrTiO}}_3$ not only creates occupied states inside the band gap but can adversely narrow the conduction band. However, if ${\mathrm{Cr}}^{3+}$ and ${\mathrm{Ti}}^{4+}$ ions are segregated in alternating [001] layers, the conduction band remains highly dispersive. This suggests that the electronic structure can be tuned by controlling the cation arrangement. We predict that ${[\mathrm{SrTiO}}_3\left]{}_{0.5}{[\mathrm{LaCrO}}_3\right]{}_{0.5}$ with alternating ${\mathrm{TiO}}_2$ and ${\mathrm{CrO}}_2$ layered along the [001] direction, which has not been experimentally realized yet, will exhibit strong absorption of visible light response and excellent electronic transport properties.

Figure 1

(a) Calculated band structure of cubic ${\mathrm{SrTiO}}_3$. The top of the valence band is positioned at 0 eV. The three $t_{2g}$ conduction bands are highlighted in cyan. (b) Illustration of pdπ interactions in the xy plane. Blue and pink shading denote the Ti $d_{xy}$ and O $p$ orbitals, respectively.

Figure 2

Density of states of ${\mathrm{STO}}_{0.5}{\mathrm{LCO}}_{0.5}$ with different $A$-site cation orderings and their structural models. The green dashed lines indicate the edges of the occupied and unoccupied states. The blue, orange, green, and purple spheres denote ${\mathrm{Ti}}^{4+},{\mathrm{Cr}}^{3+},{\mathrm{Sr}}^{2+}$, and ${\mathrm{La}}^{3+}$ cations, respectively. Oxygens are omitted for clarity. Ti-O and Cr-O bonds are shown as sticks.

Figure 3

Calculated density of states of ${\mathrm{STO}}_{1-x}{\mathrm{LCO}}_x$ solid solutions (left) and structural models (right) for $x$ = 0, 0.037, 0.125, 0.25, and 0.5. The green dashed lines indicate the edges of the occupied and unoccupied states. The tops of the oxygen $2{}_p$ states at each concentration are aligned at 0 eV. The blue and orange spheres in the structural models denote ${\mathrm{Ti}}^{4+}$ and ${\mathrm{Cr}}^{3+}$ cations, respectively. ${\mathrm{Sr}}^{2+},{\mathrm{La}}^{3+}$, and ${\mathrm{O}}^{2-}$ ions are omitted for clarity.

Figure 4

Structural models for different cation arrangements in ${\mathrm{STO}}_{0.75}{\mathrm{LCO}}_{0.25}$ (upper panel) and ${\mathrm{STO}}_{0.5}{\mathrm{LCO}}_{0.5}$ (lower panel) with their calculated band structures. In the structural models, ${\mathrm{Sr}}^{2+},{\mathrm{La}}^{3+}$, and ${\mathrm{O}}^{2-}$ ions are omitted for clarity. In the band structure plots, orange lines denote the occupied ${\mathrm{Cr}}^{3+}$ states and the cyan curves denote Ti $t_{2g}$ states. The tops of the oxygen $2{}_p$ states are aligned at 0 eV.

Figure 5

Enlarged view of the three spin-up Ti $t_{2g}$ bands in ${\mathrm{STO}}_{0.5}{\mathrm{LCO}}_{0.5}$ (A) (left) and their spatial character at the Γ point (right). The blue, green, and red curves in the band structure plot and the blue, green, and red shaded isosurfaces denote the $d_{xy},d_{xz}$, and $d_{yz}$ states, respectively.

Figure 6

A schematic illustration of the electron hopping process.