Direct determination of the coexistence region in the solid solutions Pb(Zr_xTi_1-x)O₃

By means of X-ray diffraction, the authors have determined directly the coexistence region near the morphotropic phase change of the PZT, where the tetragonal and the rhombohedral phases coexist. In this region the lattice parameters of each phase do not change, and the relative amounts obey the leverage rule. The authors show that the morphotropic phase change may be considered as a first-order transition as a function of the temperature and the chemical potential (and not the concentration, as often supposed).