The precursor dynamics of a cubic-tetragonal ferroelectric phase transition of potassium tantalate niobate ͑KTa 1−x Nb x O 3 with x = 0.32͒ crystals is studied by Brillouin scattering. The appearance of the central peak ͑CP͒ and marked softening of the elastic constant c 11 are clearly observed above the Curie temperature, T C-T , owing to the interaction between the LA mode and local polarization fluctuations of polar nanoregions ͑PNRs͒. The relaxation time determined by the CP width clearly shows a critical slowing down above T C-T , indicating an order-disorder feature of the ferroelectric phase transition. The size of a dynamic PNR is evaluated, and it increases toward T C-T .

High-density perovskite titanate zirconate-modified potassium niobate solid solutions 0.92(Na0.5K0.5)NbO3–xBaZrO3–(0.08-x)(Bi0.5K0.5)TiO3 (BBK) and Mn-added BBK have been prepared by the solid-state reaction method. The phase diagram summarized from the dielectric measurement reveals that there exists a tetragonal–rhombohedral morphotropic phase boundary (MPB) for both solid solutions. The piezoelectric properties show enhanced behavior at around the tetragonal–rhombohedral MPB. Mn addition could increase Q m as well as k p and d 33. The behavior is attributed to oxygen vacancy formation and grain size growth, respectively.

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For the development of lead-free piezoelectric ceramics, which have a tetragonal–rhombohedral morphotropic phase boundary (MPB), 0.90(Na0.5K0.5)NbO3–xBaZrO3–(0.10 - x)(Bi0.5Li0.5)TiO3 ceramics have been synthesized by the conventional solid state reaction method. A phase diagram was summarized from the X-ray diffraction pattern and the dielectric measurements. It is found that 0.90(Na0.5K0.5)NbO3–xBaZrO3–(0.10 - x)(Bi0.5Li0.5)TiO3 ceramics have an MPB between x = 0.07 and 0.08. In the vicinity of the MPB, it was observed that the dielectric and piezoelectric properties were enhanced.

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