Temperature stability and low dielectric constant of Li+ substituted Mg2Al4Si5O18 ceramics

The Mg2Al4Si5O18 ceramic is considered as one of the ideal candidates for millimeter wave communication substrate. In this work, the Mg2-xLi2xAl4Si5O18 (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.10) ceramics were synthesized via the solid-state reaction method. The phase composition, crystal structure, and microwave dielectric properties were investigated. The XRD patterns presented Mg2Al4Si5O18 with an orthorhombic structure as the main phase. Samples contain MgAl2O4 and Al2SiO5 second phases at x = 0.02, whereas the LiAlSi2O6 phase was also observed with x = 0.10. The densification of the samples was influenced by the Li2O additive. The dielectric constant (er) is dominated by the relative density and the second phase. And the densification and packing fraction are responsible for the Qf value, while second phases and bond valence of Mg-site determine temperature coefficient of resonance frequency (tf). Ultimately, the Mg1.96Li0.08Al4Si5O18 ceramics sintered at 1380.C with the satisfactory microwave dielectric properties ( er = 4.43, Qf = 17,595 GHz, and tf = 4.0 ppm/. C) were achieved, which possessed high temperature stability and low transmission delay time.

Automated summary

In this study, Mg2-xLi2xAl4Si5O18 ceramics were synthesized and their phase composition, crystal structure, and microwave dielectric properties were investigated. The addition of Li2O influenced the densification of the samples, while the relative density and second phase determined the dielectric constant. The densification and packing fraction affected the Qf value, while the second phase and bond valence of the Mg-site determined the temperature coefficient of resonance frequency.