Yuanming Lai,Caiyun Hong,Lichuan Jin,Xiaoli Tang,Huaiwu Zhang,Xin Huang,Jie Li,Hua Su
In this work, a series of low-temperature-firing (1− x )Mg 2 SiO 4 – x Li 2 TiO 3 –8 wt% LiF ( x = 35–85 wt%) microwave dielectric ceramics was prepared through conventional solid state reaction. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed that the Li 2 TiO 3 phase was transformed into cubic phase LiTiO 2 phase and secondary phase Li 2 TiSiO 5 . Partial substitution of Mg 2+ ions for Ti 3+ ions or Li + Ti 3+ ions increased the cell volume of the LiTiO 2 phase. The dense microstructures were obtained in low Li 2 TiO 3 content ( x ≤ 65 wt%) samples sintered at 900 °C, whereas the small quantity of pores presented in high Li 2 TiO 3 content ( x ≥ 75 wt%) samples sintered at 900 °C and low Li 2 TiO 3 content ( x = 45 wt%) sintered at 850 and 950 °C. Samples at x = 45 wt% under sintering at 900 °C for 4 h showed excellent microwave dielectric properties of ε r = 10.7, high Q × f = 237,400 GHz and near-zero τ f = − 3.0 ppm/°C. The ceramic also exhibited excellent chemical compatibility with Ag. Thus, the fabricated material could be a possible candidate for low temperature co-fired ceramic (LTCC) applications.
Mg2SiO4holds promise for its application in the microwave communication field due to its low dielectric constant and highQ×fvalue. However, its high negativeτfand high sintering temperature limit its application in low-temperature co-fired ceramic (LTCC) devices. In this work, Li2TiO3and CaTiO3were introduced to improve theτf, and LiF was chosen to decrease the sintering temperature. According to XRD patterns and SEM micrographs, the ceramic systems displayed a complex-phase structure, and the microstructure was densified when CaTiO3was added. All of the relative densities, dielectric constants, andQ×fvalues first increased and then decreased as the sintering temperature increased. The MLLC11.5 ceramics sintered at 800 °C could be obtained with the highestQ×fvalue of 54,581 GHz (at 8.06 GHz),εrof 14.13, andτfof + 5.81 ppm/°C. Furthermore, it was proven that the MLLC11.5 powders could be co-fired without any reaction with Ag powders at 800 °C, indicating its potential for LTCC application. The MLLC11.5 composition was used to prepare a GPS antenna and showed good prospects for its application in electronic communications.Keywords:Mg2SiO4-Li2TiO3-LiF-CaTiO3ceramics;structure;microwave dielectric property;LTCC;antenna
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