Ab initio phonon calculations for the nonpolar reference structures of the (001), (110), and (111) ${\mathrm{PbZrO}}_3/{\mathrm{PbTiO}}_3$ [1:1] superlattices are presented. The unstable polar modes in the tetragonal (001) and (110) structures are confined in either the Ti- or the Zr-centered layers and display two-mode behavior, while in the cubic (111) case one-mode behavior is observed. Instabilities with pure oxygen character are observed in all three structures. The implications for the ferroelectric behavior and related properties are discussed.

• Received 14 January 2002

DOI:https://doi.org/10.1103/PhysRevB.65.224106