Study On Ba_6-3x(Nd_1-yBi_y)_8+2xTi₁₈O₅₄ System Ceramics Of Low Temperature Sintering

For the purpose to prepare middle or high permittivity LTCC ceramic materials, Ba_6-3x(Nd_1-yBi_y)_8+2xTi₁₈O₅₄ （x=2/3, 0≤y≤1） （BNTB） system ceramics were selected as the research objects in this dissertation. The sintering temperature of BNTB system ceramics was reduced by adding different sintering aids. The effects of different sintering aids and experimental techniques on sintering behavior, phase composition, microstructure, dielectric properties and the low temperature sintering mechanisms were studied systematically. Research contents and results are as follows:1. The addition of Bi₂O₃-TiO₂ composite oxide can decrease the sintering temperature of Ba_6-3x(Nd_1-yBi_y)_8+2xTi₁₈O₅₄ （x=2/3,y=0.2） （BNTB0.2） ceramic to 1160℃, which was caused by the Bi₂O₃ liquid phase and Bi₂O₃-TiO₂ eutectic liquid phase. The addition of CaO-B₂O3-SiO₂ （CBS） glass and Li2O-B₂O3-SiO₂ （LBS） glass can decrease the sintering temperature of BNTB0.6 ceramic to below 900℃. The melting point of CBS glass is about 700℃and the melting point of LBS glass is 744℃, which can form liquid phase at low temperature and promote the sintering process of BNTB0.6 ceramic. The substitution of Ba ions in BNTB0.6 by Ca ions in CBS glass and the reaction between LBS glass and BNTB0.6 ceramic to produce Li_0.5Nd_0.5TiO₃ can accelerate the sintering of ceramic. The combined addition of LBS glass and LiF-BaF2 can decrease the sintering temperature of BNTB0.6 ceramic to 850℃. The substitution of oxygen ions in LBS glass structure by F ion in LiF-BaF2 can disaggregate the anion conglomeration, which can decrease the viscosity of LBS molten glass and accelerate the liquid phase sintering process.2. With the increase of Bi₂O₃-TiO₂ composite oxide, theεr andτεof BNTB0.2 ceramic increase, which was caused by the increase of unit cell volume of BNTB0.2 ceramic and the substitution of Nd ions in BNTB0.2 by Bi ions in Bi₂O₃-TiO₂. The tanδof BNTB0.2 ceramic first decrease and then increase. As for BNTB0.6 ceramic doped with CBS glass and LBS glass, with the growth of grains, the decrease of pores, the increase of density, the dielectric constant of BNTB0.6 ceramic increased and the dielectric loss of BNTB0.6 ceramic decreased. The excessive CBS glass and LBS glass led to the increase of pores and the decrease of density, which caused the decrease of dielectric constant and the increase of dielectric loss. The abnormal grain growth of BNTB0.6 ceramic would also caused the increase of dielectric loss.3. The effects of experimental techniques on the sintering behavior, microstructure and dielectric properties of BNTB0.6 ceramic doped with 10.0 wt% LBS glass and 1.0 wt% LiF-BaF2 were studied systematically. The optical properties were achieved when presintering temperature is 1000℃, milling time is 10h, sintering temperature is 850℃and soaking time is 2h.4. Three kinds of dielectric ceramics which had excellent properties were acquired. （1） The BNTB0.6 ceramic doped with 7.0 wt% CBS glass sintered at 875℃for 2h had excellent dielectric properties ofεr=73.34, tanδ=0.003,τε=（?）17ppm/℃. （2） The BNTB0.6 ceramic doped with 10.0 wt% LBS glass sintered at 875℃for 2h had excellent dielectric properties ofεr=75.34, tanδ=0.003,τε=（?）26ppm/℃. （3） The BNTB0.6 ceramic doped with 1.0 wt% LiF-BaF2 and 10.0 wt% LBS glass sintered at 850℃for 2h had excellent dielectric properties ofεr=75.89, tanδ=0.002,τε=（?）24ppm/℃.