Structure and dielectric dispersion in cubic-like 0.5K 0.5 Na 0.5 NbO 3 -0.5Na 1/2 Bi 1/2 TiO 3 ceramic

The nature of the cubic-like state in the lead-free piezoelectric ceramics 0.5K 0.5 Na 0.5 NbO 3 -0.5Na 1/2 Bi 1/2 TiO 3 (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 P 4 bm 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.