A tetragonal-to-monoclinic phase transition in a ferroelectric perovskite: the structure of PbZr0.52Ti0.48O3.

A tetragonal-to-monoclinic phase transition in a ferroelectric perovskite: the structure of PbZr0.52Ti0.48O3.



The perovskite-like ferroelectric system PbZr1−xTixO3 (PZT) has a nearly vertical morphotropic phase boundary (MPB) around x= 0.45-0.50. Recent synchrotron x-ray powder diffraction measurements by Noheda et al. [Appl. Phys. Lett. 74, 2059 (1999)] have revealed a new monoclinic phase between the previously-established tetragonal and rhombohedral regions. In the present work we describe a Rietveld analysis of the detailed structure of the tetragonal and monoclinic PZT phases on a sample with x= 0.48 for which the lattice parameters are respectively: at= 4.044 ˚ A, ct= 4.138 ˚ A, at 325 K, and am= 5.721 ˚ A, bm= 5.708 ˚ A, cm= 4.138 ˚ A, β= 90.496o, at 20K. In the tetragonal phase the shifts of the atoms along the polar [001] direction are similar to those in PbTiO3 but the refinement indicates that there are, in addition, local disordered shifts of the Pb atoms of ∼0.2 ˚ A perpendicular to the polar axis. The monoclinic structure can be viewed as a condensation along one of the h110i directions of the local displacements present in the tetragonal phase. It equally well corresponds to a freezing-out of the local displacements along one of the h100i directions recently reported by Corker et al. [J. Phys. Condens. Matter 10, 6251 (1998)] for rhombohedral PZT. The monoclinic structure therefore provides a microscopic picture of the MPB region in which one of the “locally” monoclinic phases in the “average” rhombohedral or tetragonal structures freezes out, and thus represents a bridge between these two phases.


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