Structure and dielectric properties of perovskite ceramics in the system Ba(Ni_(1/3)Nb_(2/3))O_3-Ba(Zn_(1/3)Nb_(2/3))O_3

摘要

Ceramics in the system Ba(Ni_(1/3)Nb_(2/3))O_3-Ba(Zn_(1/3)Nb_(2/3))O_3 (BNN-BZN) were prepared by the mixed oxide route Powders were mixed and milled, calcined at 1100-1200 deg C then pressed and sintered at temperatures in the range 1400-1500 deg C for 4 h. Selected samples were annealed or slowly cooled after sintering Most products were in excess of 96 percent theoretical density. X-ray diffraction confirmed that all specimens were ordered to some degree and could be indexed to hexagonal geometry Microstructural analysis confirmed the presence of phases related to Ba_5Nb_4O_(15) and Ba_8Zn_1Nb_6O_(24) at the surfaces of the samples. The end members BNN and BZN exhibited good dielectric properties with quality factor (Qf) values in excess of 25,000 and 50,000 GHz, respectively, after rapid cooling at 240 deg C h~(-1) In contrast, mid-range compositions had poor Qf values, less than 10,000GHz, However, after sintering at 1450 deg C for 4h and annealing at 1300 deg C for 72 h, specimens of 0.35(Ba(Ni_(1/3)Nb_(2/3))O_3)-0.65(Ba(Zn_(1/3)Nb_(2/3))O_3) exhibit good dielectric properties: tau_f of +0,6 ppm deg C~(-1), relative permittivity of 35 and quality factor in excess of 25,000 GHz, The improvement in properties after annealing is primarily due to an increase in homogeneity.