Abstract
Ceramics with low dielectric constant are widely used in high frequency substrates. The low temperature sintered CaMg0.9-xNa2xLi0.2Si2O6(x = 0–0.05 and 0.1) ceramics with low dielectric constant and dielectric loss were prepared by the traditional solid-state reaction method, with 0.5wt%LBSCA additive. The XRD patterns of the samples were obtained by X-ray diffraction and it was found that there were three ceramic components, CaMgSi2O6, CaSiO3 and Na2MgSiO4, which indicated that the experimental sample was a multiphase ceramic system. Through the trend of bulk density as functions of the content of substitution and the change of SEM morphology, it could be found that appropriate amount of Na+ substitution can promote the grain growing and the densification of ceramics. Results demonstrated that both the Q × f and εr were relevant to bulk density and the second phase. The τf was also affected by the second phase to some extent. In particular, the ceramics sintered at 925 °C for 3h possessed the desirable microwave dielectric properties for LTCC application: εr = 7.03, Q × f = 17,956 GHz, and τf= −79 ppm/°C.
Highlights
Dielectric ceramics have been widely used in microwave devices because of their low dielectric loss, serialized dielectric constant and temperature coefficient of resonant frequency which can be adjusted to near zero
It is obvious that all the specimens are polycrystalline system: diopside CaMgSi2O6(PDF#11-0654, space group: C2/c(15)) with monoclinic structure occupied the main phase, accompanied by a small amount of second phase CaSiO3(PDF#19-0249, space group:P1(1)) when x value changes from 0 to 0.1; When x0.04, the phase Na2MgSiO4(PDF#19-0249) was produced, indicating the limited solid solubility of Na+ in the CaMgSi2O6 ceramics that is resulted from the relative big radius difference between Na+(1.13Å) and Mg2+(0.72 Å)
It could be seen from the curves that the bulk density changes with the sintering temperature which is in the range of 900-950 Ԩ due to the densification process
Summary
Dielectric ceramics have been widely used in microwave devices because of their low dielectric loss, serialized dielectric constant and temperature coefficient of resonant frequency which can be adjusted to near zero. LTCC technology, which requires sintering temperature below 950Ԩ, has been paid more attention in the research of microwave dielectric ceramics to follow the development trend of device miniaturization and integration[3,4,5]. Lai et al reported that Cu2+ substituting for Mg2+ could effectively reduce the sintering temperature as well as the dielectric loss[10]. The influence of Na+ on the properties and composition of CaMgSi2O6 ceramics has not been investigated yet. Recent reports have found that the substitution of Na+ for Mg2+ improved the properties and reduced the sintering temperature of MgWO4 ceramics[1]. The phase composition, microstructure and microwave dielectric properties of the prepared ceramic samples were further investigated
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