Soft antiferroelectric fluctuations in morphotropic PbZr _1-xTi_xO₃ single crystals as evidenced by inelastic x-ray scattering

Lattice dynamics of a PbZr_1-xTi_xO₃ single crystal with composition close to the morphotropic phase boundary has been investigated by inelastic x-ray scattering. Dispersion curves of the lowest frequency transverse optic and the transverse acoustic phonon modes propagating along the [100] direction have been determined in the high-temperature paraelectric phase as well as in the room-temperature monoclinic phase. The measurement also reveals that upon cooling from the paraelectric to monoclinic phase, the spectral response of the M_5′ zone boundary phonon mode associated with antiferroelectric vibrations of lead ions is progressively transforming to a broad central mode. This indicates a crossover from vibrational to relaxational-type dynamics. The existence of this phenomenon previously observed in relaxor materials is a striking result for PZT and it is believed to arise from the nanoscale structural inhomogeneity of these materials.