| In recent years, to meet the needs of future MLCC, thinner dielectric layers are necessary. To achieve this goal, the grain size and uniformity of the MLCC particles must be effectively controlled. Whether the ferroelectricity still maintain when the grain size decreases, is the biggest obstacle in the utilization of dielectric property of nanosized ferroelectric. Therefore, the development of electronic ceramic materials of X8R-type MLCC that has the dense, fine-grained and uniform has become a hot research in this field. The article obtained the monodisperse Ba1-3x/2BixTiO3 micro/nano powder by hydro-phase method at atmospheric pressure, and obtained Ba0.991Bi0.006TiO3@Nb2O5 particles and Ba0.991Bi0.006TiO3@Nb205-Co304 particles by means of a precipitation-based coating method. Finally, the article obtained the X8R-type MLCC dielectric ceramic material with the dense, fine-grained and uniform grain.The main content of this paper as shown below:1. The micro/nano Ba1-3x/2BixTiO3 particles by hydro-phase method at atmospheric pressure to control the dispersion and particle size, and systematically research the effect of Bi content, concentration of NaOH and reactant on the phase structure and morphology, and also studied effect of Bi content on Ba1-3x/2BixTiO3 ceramics. The experimental results show that: the microstructure, particle size and particle size distribution of Ba1-3x/2BixTiO3 particles can be controlled by different reaction conditions. The particle size showed little difference with the increasing of the Bi content, but decreased with the increasing of the concentration of NaOH and reactant. The micro/nano Ba1-3x/2BixTiO3 particles were obtained with well dispersity. Average particle size of the controllable prepared Ba1-3x/2BixTiO3 nanoparticles is from 50 to 600 nm. In the study of the doping amount range,Tc of Ba1-3x/2BixTiO3 ceramics shifts to lower temperatures with the increasing of Bi content. When the x=0.006, the dielectric constant is 1964, and the dielectric constant at Tc can reach 5436.2. The monodispersed micro/nano Ba0.991Bi0.006TiO3 particles were coated by Nb2Os layer via precipitation method. The effects of the coating amount of Mb2O5 on the microstructure and phase constitution of Ba0.991Bi0.006TiO3@Nb2O5 ceramics system were also investigated. The experimental results show that:the monodispersed micro/nano Ba0.991Bi0.006TiO3 particles (-233 nm) form a core that was coated with a homogeneous Nb2O5 layer, and when the Nb2Os content exceeded 0.8 mol%, Ba0.991Bi0.006TiO3 and Nb2O5 phases coexisting in the grains. When the Ba0.991Bi0.006TiO3@Nb2O5 ceramics were sintered at 1180℃, dense, fine-grained Ba0.991Bi0.006TiO3-based ceramics (≤250 nm) were obtained. The ceramics met the X8R requirements, with a maximum dielectric constant of 2336, and a low dielectric loss at room temperature (<2.0%, with a minimum of 0.5%).3. The monodispersed micro/nano Ba0.991Bi0.006TiO3 particles were coated by Nb2os-Co3O4 composite oxide layer via precipitation method. The effects of the coating amount of Nb/Co, Nb2O5-Co304 content, calcination temperature, and sintering temperature on the microstructure and phase constitution of Ba0.991Bi0.006TiO3@Nb2O5-Co3O4 ceramics system were also investigated. The experimental results show that:as the Nb/Co and Nb2O5-Co3O4 coating amount increased, the dielectric constant of Ba0.991Bi0.006TiO3@Nb2O5-Co3O4 ceramic system showed a trend of increasing at room temperature, and with the calcination and sintering temperature increased, the density of Ba0.991Bi0.006TiO3@Nb2O5-Co3O4 ceramic system increased, and the grain grew up abnormally. Within the study all the conditions, fine-grained Ba0.991Bi0.006TiO3@Nb2O5-Co3O4 ceramics (～248.2 nm) with a maximum dielectric constant of 2832, and a low dielectric loss at room temperature of 0.89% were obtained, with Nb/Co=2:1, Nb2O5-Co304 coating amount 1.6 mol%, calcination temperature 750 ℃ and the sintering temperature 1160 ℃.Therefore, the experiment obtained the dielectric ceramic material of X8R-type MLCC with the dense, fine-grained and uniform grain. |
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