Model-dependent polar catastrophe scenario in ABO₃/SrTiO₃ (001) (A = La, Y, Sc, B = Al, Ga) systems

We have theoretically studied the structural and physical properties of ABO₃ (A = La, Y, Sc, B = Al, Ga) films on SrTiO₃ (001) crystals with SrO and TiO terminations under the assumption of epitaxially strained growth. To loosen the epitaxial condition, we have studied periodic $√2×√2$ in-plane superstructures to accommodate strain by tilting of octahedra as well as distortion. We also have studied spin-independent and spin-dependent calculations to monitor the possible magnetic ground states. The data show that spin-polarized Ti ions promote metal–insulator transition toward thinner ABO₃/SrTiO₃ compared to the nonmagnetic cases. Besides, octahedral distortions in the grown films favor a⁻a⁻c⁻ orientations to accommodate lattice mismatch, reducing the ferroelectric polar nature by antisymmetric octahedral ionic coordinates, as well as overall monoclinic-like distortion along the growth direction to accommodate strains as A atoms get smaller.