LATTICE INSTABILITIES OF BaTiO₃/SrTiO₃ ARTIFICIAL SUPERLATTICE

ABSTRACT

We have investigated lattice instabilities of ultra-short period BaTiO₃/SrTIO₃ (BTO/ STO) artificial superlattice (double-perovskite 10-atom unit cell) as a function of epitaxial strain using first-principles density functional theory (DFT) calculations based on pseudopotentials and a plane-wave basis. We find a structural transition from the tetragonal phase at compressive strain to the monoclinic phase at tensile strain. In the tetragonal phase, the Ti ions displacement patterns of the BTO/STO superlattice show ferrielectric phase behavior. Likewise, those of the monoclinic BTO/STO superlattice along [001] direction are very similar to the tetragonal BTO/STO superlattice. However, the displacement patterns in the xy-plane BTO/STO superlattice exhibit different behavior which both Ti ions displace parallely along [110] direction and against direction of oxygen displacements. It means that the monoclinic phase of BTO/STO superlattice is ferrielectric along [001] direction similar to tetragonal BTO/STO superlattice, but is ferroelectric in the xy-plane.

Keywords:

• Artificial superlattice
• BaTiO₃
• SrTiO₃
• misfit strain
• lattice instability

Acknowledgment

This work is partially supported by the Ministry of Science and Technology through the National Research Laboratory program and Ministry of Trade, Industry and Energy through system IC2010 program (SC03-02024-017-0-00).