Microwave Dielectric Properties of (Sr(1-x)A(x))2(Zn1-xBx)Si2O7 Ceramics (A = Ca, Ba and B = Co, Mg, Mn, Ni)

Abstract

The (Sr(1-x)A(x))(2)(Zn1-xBx)Si2O7 ceramics (A=Ca, Ba and B = Co, Mg, Mn, Ni) were prepared by the conventional solid-state ceramic route and their structure and microwave dielectric properties were investigated. The majority of the compositions have an akermanite-type structure except for A/B = Ba/Zn and Sr/Ni. A structural change is observed from tetragonal to monoclinic with the increase in Ba2+ content at the Ca-site. When Zn2+ was completely replaced by Ni2+, a mixture of SrSiO3 and NiO phases resulted instead of the solid solution Sr2NiSi2O7. The variation of cell parameters and cell volumes of (Sr(1-x)A(x))(2)(Zn1-xBx)Si2O7 was studied for various compositions (x) in the range 0-1. Excellent dielectric properties (epsilon(r) = 8.4, Q(u) x f = 105 000 GHz (at 12.628 GHz) and tau(f) = -51.5 ppm/degrees C) were obtained for the composition Sr2ZnSi2O7 when sintered at 1475 degrees C/2 h. Addition of 2 wt% of SrTiO3 to Sr2ZnSi2O7 decreased the tau(f) value to -13 ppm/degrees C with epsilon(r)=8.8, Q(u) x f = 60 000 GHz (at 12.585 GHz). Thus, a composite of Sr2ZnSi2O7 and SrTiO3 is a possible material for millimeter-wave communication systems and as microwave substrates.