Anelastic and dielectric study of the phase transformations of PbZr1-xTixO3 around the morphotropic phase boundary

A revival of the interest on the morphotropic phase boundary of the PbZr1-xTixO3 started after a neutron diffraction study revealed the existence of a monoclinic phase (M) bridging the tetragonal (T) and rhombohedral (R) ones. In addition, the M phase has been found to exhibit a low temperature transformation, possibly involving rotations of the oxygen octahedra, raising a debate on its nature. Finally, the rotational instability has been predicted to extend also in the T phase. We present measurements of the complex dielectric susceptibility and elastic compliance of PbZr1-xTixO3 with 0.455less-than-or-equals, slantxless-than-or-equals, slant0.53 which bring new information on the low temperature phase transformations. The T–M transition gradually changes from first- to second-order increasing the Ti content from the boundary with the R phase to x=0.48, confirming that the coexistence of T and M phases found by neutron diffraction is intrinsic and not due to compositional fluctuations. Strikingly, the T–M transformation causes a peak in the elastic compliance, whose amplitude may even exceed that of the jump at the cubic-to-tetragonal transition, as if it were a ferroelastic transformation; it is shown that indeed there is linear coupling between shear strain and order parameter, when the T–M transition mainly consists of a rotation of the polarization. The instability involving rotation of the octahedra below 200 K is visible both in the dielectric and anelastic losses, and it extends in the tetragonal phase, as predicted by recent first-principle calculations.