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. Ba1-xMgxAl2Si2O8 (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 and tau(f) of Ba1-xMgxAl2Si2O8 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 Ba1-xMgxAl2Si2O8 sintered at 1400 degrees C exhibits a high QXf value of 16461 GHz, epsilon(r)=6.44 and tau(f)=-30.6 X 10(-6) K-1 at x=0.1. The dielectric constant of Ba1-xMgxAl2Si2O8 ceramics is related with its Mg2+ polarizability and its structure. The effect of electronegativity, the size of ions and the crystal structure on Qxf value of Ba1-xMgxAl2Si2O8 ceramics are also discussed.