Fabrication and microstructure of preferential orientated 1:1 ordered Ba(Mg_1/3Nb_2/3)O₃ complex perovskite microwave dielectric ceramics by laser floating zone technique

Dense Ba(Mg_1/3Nb_2/3)O₃ complex perovskite ceramics have been successfully fabricated by directional solidification using a laser floating zone (LFZ) technique with various pulling rates. The crystal structure, microstructure, and especially ordering structure are thoroughly investigated by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The LFZ solidified rods are all of the fcc lattice structure with Fm3‾m space group resulting from B-site 1:1 cation ordering in comparison to the hexagonal structure associated with 1:2 ordering prepared by conventional sintering. The 1:1 ordering domains are formed based on the space charge model and separated by anti-phase domain boundaries related to reducing pure translational symmetry upon phase transition. Preferential orientations that <110> directions in the fcc unit cell align along the growth direction (//ND) exist in all the LFZ solidified rods. The slightest deviation is obtained with 75 μm/s pulling rate. The preferential orientated 1:1 ordered ceramics are expected to adopt properties superior to the conventional sintered polycrystalline counterparts.