Study On Structure And Microwave Dielectric Properties Of Ca（Mg,Al）（Si,Al）₂O₆ Ceramics

Ca(Mg,Al)(Si,Al)2O6 ceramics were systhesized by the solid-state route using Ca CO3、Si O2、Al2O3 and Mg O as raw materials and the structure of Ca(Mg,Al)(Si,Al)2O6 was studied. The sintering behavior and dielectric propertities of Ca(Mg,Al)(Si,Al)2O6 ceramics were improved by ion-doping method and the τf of Ca(Mg,Al)(Si,Al)2O6 ceramics were adjusted to near zero by adding Ti O2 and Ca Ti O3. Low-temperature sintering and properties of Ca(Mg,Al)(Si,Al)2O6 ceramics were investigated using sintering aids. The results are as follows:(1) Ca(Mg,Al)(Si,Al)2O6 can be acquired through Al3+ substitution for Mg2+ in Ca Mg Si2O6 structure and Ca(Mg,Al)(Si,Al)2O6 is chain silicate,crystallizing in monoclinic symmetry with a space group of C2/c, where a =9.732?, b = 8.867?, c = 5.279?, α = γ = 90 o and β =106.29 o.(2) The solubility limit of Al2O3 in Ca(Mg1-x Alx)(Si1-x/2Alx/2)2O6, which is defined as x, was between 0.15 and 0.2, and a second phase of Ca Al2 Si O6 presented when the x value reached 0.2. Good microwave dielectric properties of ?r=7.89,Q×f=59,772 GHz and τf =-42.12ppm/℃ were obtained for the ceramics with the composition of x =0.08 sintered at 1275℃.(3) In Ca(Mg0.92-x Cox Al0.08)(Si0.96Al0.04)2O6 ceramics system, the main phase of the ceramics is Ca(Mg,Co,Al)(Si,Al)2O6 when x value is below 0.4 and Ca Co Si2O6 becomes the primary phase when x value excesses 0.5. The ceramics with x value of 0.92 can be sintered at 1150 ℃ and processed good dielectric propertities; The substitution of Zn2+ for Mg2+ can markedly lower the sintering temperature of Ca(Mg0.92-x Znx Al0.08)(Si0.96Al0.04)2O6 ceramics and broaden its sintering temperature range.(4) The control of the temperature coefficient of resonant frequency(τf) could be achieved by varying the content of Ti O2 or Ca Ti O3. Particularly, Ti O2 reacted with the main ceramic phase of Ca(Mg,Al)(Si,Al)2O6 and produced secondary phases,which lowered the Q×f values of the ceramics. Ca Ti O3 just existed as a separate component in the composite and had a higher τf value, which was more effective than Ti O2 addition to tailor the τf to 0 ppm/℃.(5) In order to low sintering temperature of Ca(Mg,Al)(Si,Al)2O6 ceramic,H3BO3, 60 Zn O-30B2O3-10 Si O2 galss and Li F were introduced to the ceramic and lower its sintering temperature to 1125 ℃, 1100℃ and 1075 ℃,respectively.