Synthesis and dielectric properties of barium tantalates and niobates with complex perovskite structure

摘要

Phase composition, degree of cation ordering, and dielectric properties of complex perovskites with general formula Ba(B'_(1/3)B"_(2/3))O_3, where B' = Mg, Zn, and Ni and B" = Nb and Ta, were analyzed.It was found that all the studied complex perovskites attained high degrees of 1:2 cation ordering at temperatures specific to each composition. A high temperature order-disorder phase transition in Ba(Zn_(1/3)Nb_2/3)O_3 occurred below 1380℃. Ba(Ni_(1/3)Nb_(2/3))O_3 (BNN) and Ba(Mg_(1/3)Nb_(2/3))O_3 (BMN) pervoskites remained 100% ordered at temperatures as high as 1500 and 1620℃ ,respectively. It was found that in BMN and BNN extrinsic factors, such as the second phase (i.e., Ba_3Nb_5O_(15)) and point defects, dominated the dielectric loss at microwave frequencies. Ba(Mg,_(1/3)Ta_(2/3))O_3 (BMT) remained single phase up to 1630℃. Above this temperature, the Ba_3Ta_5O_(15) second phase was detected. A decrease in the 1:2 cation ordering and increase of dielectric loss in BMT occurred at sintering temperatures above 1590℃. It was also revealed by electron paramagnetic resonance that all samples studied contained a substantial amount of paramagnetic point defects. These defects contributed to extrinsic dielectric loss at microwave frequencies, thus degrading the Q factor.