Structure, stability, and electronic properties of $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3∕\mathrm{La}\mathrm{Al}{\mathrm{O}}_3$ and $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3∕\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_3$ interfaces

Density functional theory by means of the mixed-basis pseudopotential method was employed to carry out electronic-structure calculations of interfaces in $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3∕\mathrm{La}\mathrm{Al}{\mathrm{O}}_3$ and $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3∕\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_3$ perovskite heterophase systems. The main objective of the work is to investigate the influence of different structural and chemical terminations of the interfaces on their electronic and adhesive properties. The investigated supercells therefore include not only interfaces with a regular perovskite stacking but also interfaces with planar stacking-fault-like defects of Ruddlesden-Popper and Magneli types. Stability of interfaces is assessed by calculating rigid and relaxed works of separation. Band offsets and Schottky barriers are determined for the insulator/insulator $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3∕\mathrm{La}\mathrm{Al}{\mathrm{O}}_3$ and the insulator/conductor $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3∕\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_3$ systems, respectively.

Figure 1

(Color online) Supercell models of the STO/LAO heterophase interfaces with four possible interface terminations: (a) $\mathrm{Sr}\mathrm{O}\text{−}\mathrm{Al}{\mathrm{O}}_2$, (b) $\mathrm{La}\mathrm{O}\text{−}\mathrm{Ti}{\mathrm{O}}_2$, (c) SrO-LaO (Ruddlesden-Popper-type defect), and (d) $\mathrm{Ti}{\mathrm{O}}_2\text{−}\mathrm{Al}{\mathrm{O}}_2$ (Magneli-type defect). Indices are for pair of two adjacent planes (see Fig. 3).

Figure 2

(Color online) Supercell models of the STO/SRO heterophase interfaces with three possible interface terminations: (a) $\mathrm{Ti}{\mathrm{O}}_2\text{−}\mathrm{Sr}\mathrm{O}$ or $\mathrm{Sr}\mathrm{O}\text{−}\mathrm{Ru}{\mathrm{O}}_2$, (b) SrO-SrO (Ruddlesden-Popper-type defect), and (c) $\mathrm{Ti}{\mathrm{O}}_2\text{−}\mathrm{Ru}{\mathrm{O}}_2$ (Magneli-type defect). Indices are for pair of two adjacent planes (see Fig. 4).

Figure 3

(Color online) Interplanar spacings along the $c$ axis in the four STO/LAO heterostructures. The graphs [(a)–(d)] correspond to the supercell models [(a)–(d)] of Fig. 1, respectively. Thick solid lines mark ideal bulk spacings in the perovskites. Symbols are DFT results from relaxed supercells, which are marked as follows. Squares, cation-cation interplanar distance; diamonds, oxygen-oxygen interplanar distance; circles connected by dotted lines, average interplanar distance. For the $\mathrm{Ti}{\mathrm{O}}_2\text{−}\mathrm{Al}{\mathrm{O}}_2$ interface in panel (d), two diamonds connected by vertical thin solid lines for each plane indicate two nonequivalent oxygen atoms.

Figure 4

(Color online) Interplanar spacings along the $c$ axis in the four STO/SRO heterostructures. The graphs [(a)–(c)] correspond to the supercell models [(a)–(c)], respectively. Symbols are marked in the same way as in Fig. 3.

Figure 5

(Color online) Binding-energy curves for the $\mathrm{Ti}{\mathrm{O}}_2\text{−}\mathrm{La}\mathrm{O}$ interface in (a) STO/LAO and the $\mathrm{Ti}{\mathrm{O}}_2\text{−}\mathrm{Sr}\mathrm{O}$ contact in (b) STO/SRO. The full and dashed lines correspond to the relaxed and rigid conditions, respectively.

Figure 6

(Color online) Local densities of states of the oxygen atoms in the (a) $\mathrm{Ti}{\mathrm{O}}_2\text{−}\mathrm{La}\mathrm{O}$ and (b) $\mathrm{Sr}\mathrm{O}\mathrm{Al}{\mathrm{O}}_2$ interfaces in the STO/LAO heterostructure. Dashed lines are the oxygen LDOS in bulk STO (bottom) and bulk LAO (top). Layers are labeled as (c) for central, (i) for interface, $(-2)$ two layers away from the interface, and $(-1)$ one layer away from the interface.

Figure 7

(Color online) Planar average and macroscopic average of the electrostatic potential in the STO/LAO system for the symmetrical but nonstoichiometric supercells with two equivalent interfaces, (a) $\mathrm{Ti}{\mathrm{O}}_2\text{−}\mathrm{La}\mathrm{O}$ and (b) $\mathrm{Sr}\mathrm{O}\text{−}\mathrm{Al}{\mathrm{O}}_2$, and (c) an asymmetrical but stoichiometric supercell containing both interfaces. The dashed vertical lines mark positions of atoms in the planes.

Figure 8

(Color online) Local densities of states of the oxygen atoms for the -SrO- interface in STO/SRO.

Figure 9

(Color online) Planar average and macroscopic average of the electrostatic potential for the -SrO- interface of STO/SRO.