Role of the interface in controlling the epitaxial relationship between orthorhombic ${\mathrm{LaInO}}_3$ and cubic ${\mathrm{BaSnO}}_3$

Epitaxial perovskite oxide interfaces with different symmetry of the epitaxial layers have attracted considerable attention due to the emergence of novel behaviors and phenomena. In this paper, we show by aberration-corrected transmission electron microscopy (TEM) that orthorhombic ${\mathrm{LaInO}}_3$ films grow in form of three different types of domains on the cubic ${\mathrm{BaSnO}}_3$ pseudosubstrate. Quantitative evaluation of our TEM data shows that $c_{\mathrm{pc}}$-oriented and $a_{\mathrm{pc}}/b_{\mathrm{pc}}$-oriented domains are present with similar probability. While continuum elasticity theory suggests that $c_{\mathrm{pc}}$-oriented domains should exhibit a significantly higher strain energy density than $a_{\mathrm{pc}}/b_{\mathrm{pc}}$-oriented domains, density-functional calculations confirm that $c_{\mathrm{pc}}$- and $a_{\mathrm{pc}}$-oriented domains on ${\mathrm{BaSnO}}_3$ have similar energies.

Figure 1

Sketch of the primitive unit cell of (a) orthorhombic ${\mathrm{LaInO}}_3$ and (b) cubic ${\mathrm{BaSnO}}_3$. (c) Scheme of the relationship between the orthorhombic (red) and pseudocubic (black) ${\mathrm{LaInO}}_3$ unit cell. The ${\mathrm{a}}^{-}{\mathrm{a}}^{-}{\mathrm{c}}^{+}$ Glazer tilt pattern describes ${\mathrm{InO}}_6$ octahedral tilt in orthorhombic ${\mathrm{LaInO}}_3$ perovskite structure, while the blue arrows are pointing at the different ${\mathrm{InO}}_6$ octahedral rotations: (d) ${\mathrm{a}}^{-}$ out-of-phase tilt around the $a_{\mathrm{pc}}={\left[100\right]}_{\mathrm{pc}}$ axis (out-of-phase tilt signifies oxygen octahedra which rotate along the pseudocubic rotational axis in opposite direction), (e) ${\mathrm{a}}^{-}$ out-of-phase tilt around the $b_{\mathrm{pc}}={\left[010\right]}_{\mathrm{pc}}$ axis, and (f) ${\mathrm{c}}^{+}$ in-phase tilt around the $c_{\mathrm{pc}}={\left[001\right]}_{\mathrm{pc}}$ axis (in-phase tilt signifies oxygen octahedra which rotate along the rotational axis in the same direction). The angle between $a_{\mathrm{pc}}$ and $b_{\mathrm{pc}}, \gamma$, equals $87.6^{\circ }$.

Figure 2

(a) Cross-sectional HRTEM image of the ${\mathrm{LaInO}}_3$ film grown on ${\mathrm{BaSnO}}_3$. HRTEM simulations are shown as insets. Corresponding magnified simulations are shown together with assigned atomic models in panels (b), (c), and (d). Fast Fourier transformed images of ${\mathrm{LaInO}}_3$ domains are shown in panels (e), (f), and (g), where blue, green, and red marked unit cells correspond to the domains I, II, and III shown in panel (a), respectively.

Figure 3

(a) HRTEM image of plan-view. (b) Fast Fourier transformation of HRTEM image where red, green, and blue correspond to reflexes specific only for $a_{\mathrm{pc}}/b_{\mathrm{pc}}$ orientation, $a_{\mathrm{pc}}/b_{\mathrm{pc}}$ orientation that is ${90}^{\circ }$ rotated in the in-plane direction compared to the previous one, and $c_{\mathrm{pc}}$ orientation, respectively. (c) RGB composite image of Bragg filtered areas for three different type of domains. (d) RGB composite threshold image of three different type of domains.

Figure 4

(a) Amplitude of the exit wave obtained from the exit wave reconstruction of the ${\mathrm{BaSnO}}_3/{\mathrm{LaInO}}_3$ interface with insets showing the atomic structures of ${\mathrm{BaSnO}}_3$ and ${\mathrm{LaInO}}_3$. Dark dots correspond to atoms. (b) Inversed contrast of the amplitude, used for oxygen atomic columns mapping. Oxygen positions used for $\gamma$ angle measurement are marked with blue dots, and extracted in panel (c).

Figure 5

HRTEM images of the ${\mathrm{LaInO}}_3$ film heated at (a) $300{}^{\circ }\mathrm{C}$, (b) $650{}^{\circ }\mathrm{C}$, and (c) $700{}^{\circ }\mathrm{C}$ (white arrows are pointing at the ${\mathrm{LaInO}}_3$ film decomposition). Corresponding fast Fourier transformed images (FFT) are overlayed in panels (a) and (b). (d) Diffraction pattern of the ${\mathrm{LaInO}}_3$ film at $750{}^{\circ }\mathrm{C}$, where red, green, and blue correspond to reflexes specific only for $a_{\mathrm{pc}}/b_{\mathrm{pc}}, a_{\mathrm{pc}}/b_{\mathrm{pc}}$ orientation that is ${90}^{\circ }$ rotated in the in-plane direction, and $c_{\mathrm{pc}}$ orientation, respectively.

Figure 6

Geometries of coherently strained $a_{\mathrm{pc}}$ [(a) and (b)], and $c_{\mathrm{pc}}$ (c) orientation of ${\mathrm{LaInO}}_3$ on top of ${\mathrm{BaSnO}}_3$ (001) surface. (a) In ${\mathrm{LaInO}}_3$, the blue shadowed region marks fixed geometry. Blue shadowed regions in ${\mathrm{BaSnO}}_3$ mark the first unit cell which has lattice parameter fixed to the bulk value.

Figure 7

Alternation of In-O bond lenghts in bulk ${\mathrm{LaInO}}_3$.