Low-temperature phase transformations of PbZr1-xTixO3 in the morphotropic phase-boundary region

We present anelastic and dielectric spectroscopy measurements of PbZr1-xTixO3 with 0.455<=x<=0.53, which provide new information on the low-temperature phase transitions. The tetragonal-to-monoclinic transformation is first order for x<0.48 and causes a softening of the polycrystal Young's modulus whose amplitude may exceed the one at the cubic-to-tetragonal transformation; this is explainable in terms of linear coupling between shear strain components and tilting angle of polarization in the monoclinic phase. The transition involving rotations of the octahedra below 200 K is visible both in the dielectric and anelastic losses, and it extends within the tetragonal phase, as predicted by recent first-principle calculations.