Ba1-xMgxAl2Si2O8晶体结构与微波介电性能的研究

采用固相烧结法, 按化学计量比Ba_1-xMg_xAl₂Si₂O₈(x=0, 0.05, 0.1, 0.15, 0.3, 0.5)制备样品, 考察不同MgO含量对BaO-Al₂O₃-SiO₂系介电材料晶体结构及微波介电性能的影响。结果表明, MgO可以降低烧结温度, 促进六方相转变为单斜相, 当添加量x≥0.15时, 相转变可以达到100%。当x≤0.15时, 适量的MgO可以有效地促进单斜钡长石晶粒的长大。在0.05≤x≤0.1范围内, 随着MgO含量的增加, 单斜钡长石衍射峰增强, 晶粒尺寸增大, 密度、介电常数与τ_f均随MgO含量的增加而增大。在x=0.1, 烧结温度为1400℃时, 可获得综合性能相对较好的单斜钡长石, 其介电性能ε_r=6.44, Q×f=16461 GHz, τ_f= -30.6×10^-6 K^-1。

Crystal Structure and Microwave Dielectric Property of Ba1-xMgxAl2Si2O8

Barium feldspar BaO-Al₂O₃-SiO₂ system materials have been studied extensively for application in microwave devices, microwave substrate and packaging in recent years, due to their remarkable dielectric properties. The hexacelsian-celsian transition, relationship between dielectric properties, and structure of BaO-Al₂O₃-SiO₂ system has attracted widely academic interest. Ba_1-xMg_xAl₂Si₂O₈ (x=0, 0.05, 0.1, 0.15, 0.3, 0.5) ceramics were prepared by solid state sintering processing. The crystal structure and microwave dielectric properties of BaO-Al₂O₃-SiO₂ with different MgO contents were studied. The results show that MgO doping reduces sintering temperature and greatly promotes the transition from hexacelisian to celsian at x≥0.15, while the transition reachs 100%. MgO doping effectively increases grain size at x≤0.15. The diffraction peak of celsian is enhanced and the grain size gets larger. Moreover, the density, dielectric constant andτ_f of Ba_1-xMg_xAl₂Si₂O₈ ceramics increases with the increase of MgO content in the range of 0.05≤x≤0.1. In addition, the resonant frequency temperature coefficient is negative. The Ba_0.9Mg_0.1Al₂Si₂O₈ sintered at 1400℃ exhibits a high Q×f value of 16461 GHz, ε_r=6.44 and τ_f= -30.6×10^-6 K^-1 at x=0.1. The dielectric constant of Ba_1-xMg_xAl₂Si₂O₈ ceramics is related with its Mg²⁺ polarizability and its structure. The effect of electronegativity, the size of ions and the crystal structure on Q×f value of Ba_1-xMg_xAl₂Si₂O₈ ceramics are also discussed.