Effect of Ga3+ Doping on Crystal Structure Evolution and Microwave Dielectric Properties of SrAl2Si2O8 Ceramic
Changzhi Yin, Mingfei CHENG, Weicheng Lei, Yiyang Cai, Xiaoqiang Song, Ming Fu, Wenzhong Lü, Wen LEI
Abstract
The feldspar-based microwave dielectric ceramic with low relative permittivity ( r ) and excellent mechanical properties has attracted much attention in the fifth-generation wireless communication technology.In this work, a series of microwave dielectric ceramic SrAl 2-x Ga x Si 2 O 8 (0.1x2.0) was synthesized using the traditional solid-state method.X-ray diffraction pattern indicates that Ga 3+ can be dissolved into Al 3+ , forming a solid solution.Meanwhile, substitution of Ga 3+ for Al 3+ can promote the space group transition from I2/c (0.1x 1.4) to P21/a (1.6x2.0)with coefficient of thermal expansion (CTE) increasing from 2.910 -6 -1 to 5.210 -6 -1 .During this substitution, the phase transition can significantly improve the structural symmetry to enhance the dielectric properties and mechanical properties.Rietveld refinement results indicate that Ga 3+ averagely occupied four Al 3+ compositions to form solid solution.All ceramics have a dense microstructure and high relative density above 95%.An ultralow r of 5.8 was obtained at x=1.6 composition with high quality factor (Qf) of 50700 GHz and negative temperature coefficients of resonant frequency ( f ) of approximately -3510 -6 -1 .The densification temperature can be reduced to 940 by adding 4% (in mass) LiF, resulting in good chemical compatibility with Ag electrode.Meanwhile, negative f can be tuned to near-zero (+3.710 -6 -1 ) by adding CaTiO 3 ceramic.