The effect of layer-by-layer heterostructuring and epitaxial strain on lattice instabilities and related ferroelectric properties is investigated from first principles for the $\left[001\right]-\left({\mathrm{PbTiO}}_3{)}_1\right({\mathrm{PbZrO}}_3{)}_1$ superlattice and pure ${\mathrm{PbTiO}}_3$ on a cubic substrate. The results for the superlattice show an enhancement of the stability of the monoclinic r phase with respect to pure ${\mathrm{PbTiO}}_3.$ Analysis of the lattice instabilities of the relaxed centrosymmetric reference structure computed within density functional perturbation theory suggests that this results from the presence of two unstable zone-center modes, one confined in the ${\mathrm{PbTiO}}_3$ layer and one in the ${\mathrm{PbZrO}}_3$ layer, which produce in-plane and normal components of the polarization, respectively. The zero-temperature dielectric response is computed and shown to be enhanced not only near the phase boundaries, but throughout the r phase. Analysis of the analogous calculation for pure ${\mathrm{PbTiO}}_3$ is consistent with this interpretation, and suggests useful approaches to engineering the dielectric properties of artificially structured perovskite oxides.

• Received 4 December 2003

DOI:https://doi.org/10.1103/PhysRevB.69.184101