Comparative study of two lead-free piezoceramics using diffraction techniques

A comparative study of two distinct lead-free piezoceramics, (Bi_0.5Na_0.5TiO₃)_0.92-(BaTiO₃)_0.06-(K_0.5Na_0.5NbO₃)_0.02 and (Bi_0.5Na_0.5TiO₃)_0.94-(BaTiO₃)_0.05-(K_0.5Na_0.5NbO₃)_0.01, termed 92-06-02 and 94-05-01, respectively, is presented. The samples were investigated by complementary diffraction techniques, namely X-ray, neutron and electron diffraction. Transmission electron microscopy (TEM) and powder diffraction experiments clearly revealed the presence of both rhombohedral and tetragonal phases in space groups R3c and P4bm, respectively. Superlattice reflections observed in the diffraction patterns were used to identify the two phases. It was found that sample 92-06-02, with a high proportion of the nonpolar tetragonal phase, shows a grainy contrast, whereas specimen 94-05-01 features domain-like contrast, related to a higher rhombohedral phase fraction. The combination of local scale analyses via TEM with X-ray and neutron diffraction provides the experimental basis for further structural investigations.