(Mg_(1-x)Ca_x)_2Al_4Si_5O_(18)陶瓷的相演变与微波介电性能

Compositional Phases and Microwave Dielectric Properties of (Mg_(1-x)Ca_x)_2Al_4Si_5O_(18) Ceramics

采用固相烧结反应法制备(Mg1-x,Cax)2Al4Si5O18陶瓷。XRD测试结果表明:0≤x<0.2时,陶瓷以(Mg,Ca)2Al4Si5O18堇青石单一相固溶体形式存在;0.2≤x<0.8时,陶瓷以Mg2Al4Si5O18/CaAl2Si2O8两相复合形式存在;0.8≤x<1.0时,陶瓷以单一相(Ca,Mg)Al2Si2O8固溶体形式存在。SEM结果显示:Ca2+掺杂可以有效地降低堇青石陶瓷的气孔率与微裂纹,并能有效地控制Mg2Al4Si5O18/CaAl2Si2O8复相陶瓷的颗粒分布与晶粒尺寸。微波介电性能测试结果表明:0≤x≤0.4时,(Mg1-xCax)2Al4Si5O18陶瓷介电常数εr为7.0左右;0.6≤x≤1.0时,εr从7.0增加到8.6,然后又降低到6.9。随着x增加,品质因数Qf值从24 100 GHz降低到4 400 GHz。但是,在x=0.6时,由于[Si,AlO4]四面体中Al/Si原子排列的有序化,(Mg0.4,Ca0.6)2Al4Si5O18陶瓷Qf值(Qf=5 500 GHz)比两侧x值成分点Qf值有较大提高。(Mg1-x,Cax)2Al4Si5O18陶瓷谐振频率温度系数在整个x值范围内保持在-20×10-6～-35×10-6℃-1。

（Mg1-xCax）2A14Si5O18 ceramics were fabricated by a conventional ceramic sintering method. The results by X-ray diffrac- tion showed that the （Mg, Ca）2A14SisO18 solid solution were formed in the range of 0≤x〈0.2, and （Ca,Mg）A12Si2O8 solid solution was formed in the range of 0.8≤x≤ 1.0, and the composite phases of both Mg2A14Si5O18 and CaAI2Si208 ceramics existed in the range of 0.2≤x〈0.8. The results by scanning electron microscopy showed that the porosity and micro-cracks of cordierite ceramics were ef- fectively suppressed, the crystal growth and particle distribution of the composite phase of Mg2A14Si5O18/CaA12Si2O8 ceramics were controlled, along with Ca^2＋ doping. The dielectric constants of （Mg1-x, Cax）zAlaSi5018 ceramics retained at 7.0 in the range of 0≤x≤ 0.4. Afterwards, it increased from 7.0 at x=0.6 to 8.6 at x=0.8 and then decreased to 6.9 at x=1.0. The Qfvalues decreased from 24100 GHz of x=O to 4400GHz of x= 1.0 in the range of 0≤x≤l. However, the Qfvalue reached 5 500GHz at x = 0.6, due to the im- provement of [Si,A104] inoic orders, which was higher than that of other compositional point in the range of 0.4≤x≤ 1.0. The tem- perature coefficients of resonant frequency （Tf） of （Mg1-x,Cax）2A14Si5O18 ceramics were -20 x 10^-6 to -35 x 10^-6 ℃-1.