Structural Studies of Ordering in the (Pb1-xBax)(Mg1/3Nb2/3)O3 Crystalline Solution Series

The ordered structures of the (Pb_{1- x} Ba _x )(Mg_1/3Nb_2/3)O₃crystalline solution series were investigated by selected area electron diffraction (SAED) and high-resolution electron microscopy (HREM). At low Ba contents (e.g., x < 0.40), the ordered structure was found to be isostructural with Pb(Mg_1/3Nb_2/3)O₃, with a doubled unit cell characterized by 1/3{111} superlattice reflections. At higher Ba contents (e.g., x > 0.60), the ordered structure was characterized by 1/3{111} superlattice reflections. For intermediate Ba contents (e.g., x - 0.60), diffuse scattering along the {111} between diffuse 1/2{111} and 1/3{111} reflections was observed. The ordering is attributed to the distribution of the B-site cations between multiple sublattices. Strong fluctuations in the B-site cation ratio between ordered and disordered regions are believed not to exist; however, the possibility of weak fluctuations is consistent with the observed lattice images.