Ruddleson-Popper phase SnO(SnTiO3)n: Lead-free layered ferroelectric materials with large spontaneous polarization

Abstract

Perovskite phase SnTiO3 was predicted to have a large spontaneous polarization of 1.1 C/m2, but its synthesis has been unsuccessful so far. Here, we calculated the ferroelectric properties of a series of Ruddleson-Popper (RP) phase SnO(SnTiO3)n (n = 1 ∼ 6), with perovskite SnTiO3 as the ending structure (n = ∞), using the first principles calculations. An analysis of RP phase tolerance factor indicated that the fabrication of the RP phase SnO(SnTiO3)n may be easier than that for SnTiO3. For bulk SnO(SnTiO3)1, the most stable phase is Aba2 with a spontaneous polarization of 0.53 C/m2 along [110]. Aba2 is also the most stable phase for SnO(SnTiO3)1 under biaxial strain. For RP phase SnO(SnTiO3)n on a SrTiO3 substrate, there is also a phase transition with the increasing layer thickness n. The polarization increases with strain or layer thickness. The ferroelectric properties and size effect in the free standing RP phase SnO(SnTiO3)n nanosheets were also investigated, and the in-plane polarization is 60% larger than that of the bulk.