Microwave dielectric ceramics Sr 2 CeO 4 + n wt% Li 2 CO 3 —Bi 2 O 3 (LB) (1 ≤ n ≤ 4, L: B = x : y , weight ratio) were prepared by a traditional solid-state reaction method. The effects of LB additives on the phase formation, microstructure, sintering behavior, and microwave dielectric properties of Sr 2 CeO 4 ceramics were investigated. The sintering temperature can be reduced obviously from 1270 to 950 °C because of the liquid phase formation of LB. Single-phase Sr 2 CeO 4 ceramics with dense structure and homogenous grains were obtained by adding 1wt% LB. With LB content increasing, Q × f values would decrease because secondary-phase SrCeO 3 appeared in the ceramics. When the content of LB was fixed at 1 wt%, the sintering temperature and Q × f value would decrease simultaneously with the ratio of Li 2 CO 3 increasing. Desirable performances of Sr 2 CeO 4 + 1wt% LB ceramics: ( ε r = 14.36, Q × f = 102,023 GHz and τ f = − 66.42 ppm/°C, L:B = 2:8) and ( ε r = 13.56, Q × f = 70,109 GHz, τ f = − 64.17 ppm/°C, L:B = 8:2) can be achieved at 1075 °C and 950 °C, respectively, suggesting that Sr 2 CeO 4 –LB ceramics have a great potential for millimeter-wave applications.
Qi Yuan,Sen Wang,Gaobin Liu,Kuoming Song,He Zhao,Shuai Yan,Xin Li
Dense MgO–12% TiO 2 (w) ceramics containing 12 wt% TiO 2 , which were doped with Li 2 CO 3 –Bi 2 O 3 composite sintering aids, were prepared at a low sintering temperature of 950 °C in this study. The effects of sintering additives on the sintering characteristics, phase composition, microstructure, and dielectric and mechanical properties of the ceramic samples were systematically investigated, and the influences of their phase composition and microstructure on the dielectric and mechanical properties were examined. The introduction of sintering aids produced a new Bi 4 Ti 3 O 12 phase in the sample structure, while the residual Bi 2 O 3 mixed with the newly formed Mg 2 TiO 4 and Bi 4 Ti 3 O 12 phases distributed at MgO grain boundaries formed a structure surrounding MgO grains. This structure filled the pores in the ceramic sample, which increased its density and enhanced the mechanical properties. At a Li 2 CO 3 –Bi 2 O 3 content of 15 wt%, the density, flexural strength , and Vickers hardness of the ceramic samples reached their maximum values of 3.4 g/cm 3 , 218.9 MPa, and 778.7 HV, respectively. However, the further increase in the Li 2 CO 3 –Bi 2 O 3 content deteriorated their dielectric properties although the dielectric constant and dielectric loss remained below 13.4 and 2.1 × 10 −3 , respectively. The findings of this work indicate that Li 2 CO 3 –Bi 2 O 3 sintering aids can significantly lower the sintering temperature of MgO–12% TiO 2 (w) ceramics and control their dielectric and mechanical properties through microstructural changes.
The NASICON-type Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) is considered to be one of the most promising solid electrolytes because of its excellent chemical stability against moisture and considerable total ionic conductivity . Nevertheless, the poor sinterability and low grain boundary ionic conductivity of LATP limit its practical commercial applications. Herein, Li 2 CO 3 ·Bi 2 O 3 (abbreviated as LB), as a sintering aid, was introduced into LATP to improve its sinterability and ionic conductivity. It was demonstrated that the addition of LB promoted the liquid phase sintering of LATP by forming the secondary phases with a low melting point, thereby promoting the growth of grains and making the contact between the grains closer. With the help of LB, the sintering temperature of LATP was reduced to about 900 °C. A series of comparative investigations indicated that the LATP-2LB ceramic pellets sintered at 900 °C exhibited the highest total ionic conductivity of 0.673 mS/cm. Meanwhile, the relative density and grain boundary ionic conductivity of LATP-2LB ceramic pellets sintered at 900 °C reached 95.28% and 3.835 mS/cm, respectively, which is much higher than 77.16% and 0.264 mS/cm of LATP-0LB ceramic pellets sintered at the same temperature. Obviously, LB can effectively improve the sinterability of LATP while increasing its ionic conductivity, providing a new strategy for preparing LATP ceramics with excellent properties.
危险品化学品经营许可证（带存储）