Abstract
In this study, low-temperature fired CaMg1−xLi2xSi2O6 microwave dielectric ceramics were prepared via the traditional solid-state reaction method. In this process, 0.4 wt% Li2CO3-B2O3-SiO2-CaCO3-Al2O3 (LBSCA) glass was added as a sintering aid. The results showed that ceramics consisted of CaMgSi2O6 as the main phase. The second phases were CaSiO3 always existing and Li2SiO3 occurring at substitution content x > 0.05. Li+ substitution effectively lowered sintering temperature due to 0.4 wt% LBSCA and contributed to grain densification, and the most homogeneous morphology could be observed at x = 0.05. The effects of relative density, the second phase, and ionic polarizability on dielectric constant (εr) were investigated. The quality factor (Q × f) varied with packing fraction that concerned the second phase. Moreover, the temperature coefficient of the resonant frequency (τf) was influenced by MgO6 octahedral distortion and bond valence. Excellent dielectric properties of the CaMg1−xLi2xSi2O6 ceramic was exhibited at x = 0.05 with εr = 7.44, Q × f = 41,017 GHz (f = 15.1638 GHz), and τf = −59.3 ppm/°C when sintered at 900 °C. It had a good application prospect in the field of low-temperature co-fired ceramic (LTCC) substrate and devices.
Highlights
Microwave dielectric ceramics constitute key materials used in microwave band communication
It could be observed that the main phase CaMgSi2O6 (PDF#11-0654) and the second phase CaSiO3 (PDF#27-1064) always existed indifferently to x (0–0.3) variation
The phase compositions detected from the X-ray diffraction (XRD) patterns, which were composed of at least two phases (CaMgSi2O6 and CaSiO3 existed when x varied from 0 to 0.3, and Li2SiO3 occurred since x exceeded 0.05), were confirmed by the Rietveld refinement results
Summary
Microwave dielectric ceramics constitute key materials used in microwave band communication (mainly from 300 MHz to 300 GHz). CaSiO3, after which, the ceramic acquired the dielectric properties of CaMgSi2O6 sintered at 1290 °C: εr = 7.46, Q × f = 59,638 GHz, and τf = −46 ppm/°C. CaMgSi2O6 ceramics were conducted to enhance the microwave dielectric properties, indifferently to sintering temperature decrease [19,20]. Li-ion substitution has been proved to be an effective method to decrease the sintering temperature of the ceramics without deterioration of properties [25,26,27,28]. Certain materials, such as Li2WO4 containing Li-ion, demonstrated an ultra-low sintering temperature [25,26,27].
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