  The nature of the cubic-like state in the lead-free piezoelectric ceramics
0.5K0.5Na0.5NbO3-0.5Na0.5Bi0.5TiO3 (KNN-50BNT) has been examined in detail by
synchrotron x-ray diffraction (SD), selected area electron diffraction (SAED),
neutron diffraction (ND), and temperature dependent dielectric
characterization. The SD pattern of KNN-50BNT presents a pure perovskite
structure with pseudocubic symmetry. However, superlattice reflections were
observed by SAED and completely indexed by tetragonal symmetry with P4bm space
group in ND pattern. The relaxor behavior of KNN-50BNT is compared with
Pb-based and Ba-based relaxors and discussed in the framework of the
Vogel-Fulcher law and the new glass model. The KNN-50BNT ceramic exhibits the
strongest dielectric dispersion among them.
