Long-range order effects in Pb(Zr1/2Ti1/2)O-3

Total energies were calculated for Pb(Zr1/2Ti1/2)O-3 (PZT) superlattices with B site cations ordered along the [001] and [111] directions within the local density approximation. The local orbital extension of the Linearized Augmented Planewave (LAPW + LO) method was used to obtain energies for the unrelaxed structures and the ab initio Potential-Induced Breathing (PIB) method was applied to establish relaxation energies. We compare the relative stabilities for the PZT superlattices, pure PbTiO3 (PT) and PbZrO3 (PZ). B site cation ordering along the [111] direction results in a lower energy superstructure than that of the [001] ordered structure. The unrelaxed [111] ordered structure results in lower energy than the average energy of the unrelaxed separate PZ and PT phases. If we expect relaxation energies of the same magnitude accompanying ferroelectric and antiferroelectric instabilities in PZ, PT and PZT, we can anticipate simultaneous competition between various processes, such as phase separation, long-range order and disorder. This richness of available structures can contribute significantly to the extraordinary properties of PZT with compositions near the morphotropic phase boundary.