Figure 1. Crystal structures of SrRuO₃ (SRO) and GdScO₃ (GSO).

Both SRO (top) and GSO (bottom) in bulk have a Pbmn orthorhombic perovskite structure with √2a_pc × √2a_pc × 2a_pc unit cell dimensions, where a_pc denotes the pseudocubic perovskite lattice parameter. In this structure, oxygen octahedra rotate in the pattern described as a⁻a⁻c⁺ in the Glazer notation, where the rotations are in-phase around the [001]_ortho axis and out-of-phase around the [1–10]_ortho axis. This indicates that the observation along the [001]_ortho direction allows for investigations of octahedral distortions in the SRO/GSO heterostructure. The black dotted and solid squares represent the unit cell for the orthorhombic and pseudocubic structures, respectively. The definition of the oxygen octahedral tilt angle θ (below 180°, blue dashed lines) is also included. When the SRO film is epitaxially grown on the GSO substrate (black arrow), some shifts of the oxygen atoms at the interface is expected (red arrows) due to the lattice and octahedral tilt angle mismatch between SRO and GSO.