Phenomenological and structural study of a low-temperature phase transition in the PbZrO3PbTiO3 system

The Landau-Ginsburg-Devonshire phenomenological theory has been applied to the PbZrO₃PbTiO₃ crystalline solid solution system to explore the behavior of the rhombohedral-tetragonal morphotropic phase boundary in the region below room temperature. The theory suggests that morphotropy is preserved, i.e., that the phase boundary occurs at nearly the same composition right down to 0 K. The rhombohedral (R3m)-rhombohedral (R3c) phase transition was investigated for a composition PbZr_0.6Ti_0.4O₃ using neutron diffraction. Structures in both phases were refined by the Rietveld profile fitting technique. The transition behavior in this composition was indicative of a diffuse-type phase transition, with a transition temperature somewhere between 250 and 300 K. The diffuse nature of this transition is perhaps due to short-range ordering of Zr and Ti. However, powder neutron diffraction is not ideal for determining critical behavior; therefore, it is difficult to make a quantitative conclusion in this respect. Values of the spontaneous polarization were obtained from the (Zr/Ti) shifts, and compared to those deduced from phenomenological theory.