The effect of cation ordering and domain boundaries on low loss Ba(BI1/3BII2/3)O3 perovskite dielectrics revealed by high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM)

Abstract High quality ceramics of Ba((Co 0.7 Zn 0.3 ) 1/3 Nb 2/3 )O 3 (BCZN), Ba(Mg 1/3 Nb 2/3 )O 3 (BMN) and Ba(Mg 1/3 Ta 2/3 )O 3 (BMT) were prepared by the mixed oxide route using sintering temperatures up to 1620 °C. Products with a high degree of cation ordering exhibited dielectric Q  ×  f values from 83,000 GHz (BCZN) to 360,000 GHz (BMT). High Resolution TEM and aberration-corrected scanning transmission electron microscopy (STEM) revealed ordering domains and type I, II and III boundary structures. High-Angle Angular Dark Field (HAADF) STEM images provided direct evidence of 1:2 ordering and stacking sequences, and the presence of disordered regions within domain boundaries. The exceptionally high Q  ×  f values for BMT are associated with a high degree of B-site ordering and the removal of domain boundaries in large, single domain grains. The catastrophic degradation of Q  ×  f values in BMN after prolonged sintering is associated with formation of a lossy ferroelectric secondary phase (Ba 3 Nb 2 O 8 ), and changes to composition and stoichiometry of BMN grains.