F. Cordero, F. Trequattrini, F. Craciun, C. Galassi
The results are presented of anelastic and dielectric spectroscopy measurements on PbZr1-xTixO3 (PZT) with compositions near the two morphotropic phase boundaries (MPBs) that the ferroelectric (FE) rhombohedral phase has with the Zr-rich antiferroelectric and Ti-rich FE tetragonal phases. Additional evidence is provided of a new phase transformation, whose temperature T_IT(x) prosecutes the long range tilt instability line T_T(x) up to T_C. It is interpreted as an initial stage of the tilt instability, and it is proposed that the difficulty of seeing the expected 1/2<111> modulations in diffraction experiments is due to the anistropy in the correlation length for octahedral tilting around <100>, which, in the presence of enhanced lattice disorder near the AFE border favours precursor clusters of octahedra that exhibit mainly 1/2<110> modulation. It is shown that the lines of the tilt instabilities tend to be attracted and merge with those of polar instabilities. Not only T_IT bends toward T_C and then merges with it, but in our series of samples the temperature TMPB of the dielectric and anelastic maxima at the rhombohedral/tetragonal MPB does not cross T_T, but deviates remaining parallel or possibly merging with T_T. These features, together with a similar one in NBT-BT, are discussed in terms of cooperative rather than competitive coupling between tilt and FE instabilities, which may trigger a common phase transition. An analogy is found with recent simulations of the tilt and FE transitions in multiferroic BiFeO3 [Kornev and Bellaiche, Phys. Rev. B 79, 100105 (2009)]. An abrupt change is found in the shape of the anelastic anomaly at TT when x passes from 0.465 to 0.48, whose possible implications on the existence of a rhombohedral/monoclinic boundary are discussed.
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http://arxiv.org/abs/1208.1618
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