TiO_2对MgO-Al_2O_3-SiO_2-TiO_2-La_2O_3系微晶玻璃相变和微波介电性能的影响

Effect of TiO_2 on Crystallization and Microwave Dielectric Properties of MgO-Al_2O_3-SiO_2-TiO_2-La_2O_3 Glass-ceramics

采用高温熔融法和-步法微晶化热处理制备了MgO-Al_2O_3-SiO_2-TiO_2-La_2O_3(MASTL)微晶玻璃。利用差热分析、X射线衍射、扫描电子显微镜和网络分析仪等手段研究了TiO_2含量对MASTL玻璃析晶相变过程、显微结构和微波介电性能的影响。结果表明,在玻璃热处理过程中先后有硅钛铈矿、金红石(TiO_2)、镁铝钛酸盐、尖晶石(MgAl_2O_4)和堇青石(Mg_2Al_4Si_5O_(18)))5种晶相析出。其中,镁铝钛酸盐含量相对较低,尖晶石是一个亚稳过渡相。随着TiO_2含量的增多,原始玻璃的析晶倾向增大,初晶相硅钛铈矿和主晶相金红石的析晶温度显著降低,而尖晶石的析晶温度升高;材料的介电常数和谐振频率温度系数均显著增大,这主要由样品中具有高介电常数(100.0)和较大正温度系数(400×10^(-6)/℃)的金红石相含量增多引起。同时,由于高品质因数相堇青石(40000GHz)的析出量略有减少,品质因数有所降低。

Glass-ceramics were fabricated from MgO-Al_2O_3-SiO_2-TiO_2-La_2O_3(MASTL) system by a molten method and subsequent one-step crystallization heat-treatment.The effect of TiO_2 on the crystallization,microstructure and dielectric properties of the glass-ceramic material was investigated by differential scanning calorimetry,X-ray diffraction,scanning electron microscopy,energy dispersive X-ray spectroscopy and network analysis,respectively.The results show that the glass-ceramic consists of multi-crystalline phases,i.e.,perrierite,cordierite,magnesium aluminotitanate(MAT),rutile and spinel(MgAl)2O_4).Among them,the content of MAT is low and spinel belongs to metastable intermediate.The crystallization tendency of the original glass becomes stronger when TiO_2 content increases.Moreover,the crystallization temperature of perrierite and rutile descends significantly,while the crystallization temperature of spinel increases.The increase of dielectric constant and temperature coefficient of resonant frequency(τ_f) of the glass-ceramic is mainly due to the presence of more rutile with greatε_r and tremendous positive τ_f,and the slight decrease of quality factor(Q×f) is correlated to the decrease of cordierite with great Q×f.