Strain effect on the ground-state crystal structure of Sr₂SnO₄ Ruddlesden-Popper oxides

Ruddlesden-Popper (RP) oxides (A_n+1B_nO_3n+1), which consist of perovskite ABO₃ slabs with AO rock-salt layers inserted between them, can exhibit diverse crystal structures. Here, we explore the lattice dynamics of Sr₂SnO₄, n=1 RP strontium stannates and investigate the strain effects on the ground-state crystal structure by employing first-principles calculations and group theoretical symmetry analyses. Dominant irrep modes are shown to be X point modes, X₃⁺, X₂⁺, X₄⁺, which correspond to octahedral rotations about different crystallographic axes and associated Sr displacements. The behavior of each unstable structural mode with irreps X₃⁺, X₂⁺, X₄⁺ and relevant order parameters with respect to imposed biaxial strain is analyzed. The predicted crystal structures are compared with earlier experimental structures of Sr₂SnO₄.