Hai-Tao Zhou,Zhe-Nan Xu,Jian-Yun Yan,Hao Huang,Yan-Bo Guo,Kang Du,Wen-Zhong Lu,Wen Lei
In the present study, (1 − x )BaAl 2 Si 2 O 8 − x CaSnSiO 5 − y wt.% LiF microwave dielectric ceramics were prepared through the traditional solid-state sintering at 950−1395°C for 5 h. The BaAl 2 Si 2 O 8 phase could coexist with the CaSnSiO 5 phase at (1 − x )BaAl 2 Si 2 O 8 − x CaSnSiO 5 (.2 ≤ x ≤ .6) ceramics, and no other secondary phase was observed. The CaSnSiO 5 , as a τ f regulator, adjusted the negative τ f value of BaAl 2 Si 2 O 8 to near zero. Excellent microwave dielectric properties ( ε r = 8.1, Q × f = 37 560 GHz, and τ f = −1.5 ppm/°C) were obtained from the 0.6BaAl 2 Si 2 O 8 −0.4CaSnSiO 5 ceramic. The sintering temperature of 0.6BaAl 2 Si 2 O 8 −0.4CaSnSiO 5 ceramic decreased from 1375°C to 950°C by introducing 2 wt.% LiF. The 0.6BaAl 2 Si 2 O 8 −0.4CaSnSiO 5 −2 wt% LiF ceramic exhibited remarkable microwave dielectric properties ( ε r = 7.6, Q × f = 17 420 GHz, and τ f = −12.2 ppm/°C) and could be applied to the low-temperature co-fired ceramic (LTCC) field.
The monoclinic CaSnSiO 5 phase could be synthesized with a conventional solid state method. The molar ratio of Ca:Sn:Si=1:1.05:1 was employed to synthesize pure CaSnSiO 5 ceramics through non-stoichiometric effect. The CaSnSiO 5 ceramics sintered at 1525 °C exhibited microwave dielectric properties : a dielectric constant ( ε r ) of 9.08, a quality factor ( Q × f ) of 61,000 GHz and a temperature coefficient of resonant frequency ( τ f ) of 35 ppm/°C. They are promising millimeter-wave ceramic materials.
Kang Du,Fei Wang,Xiao-Qiang Song,Yan-Bo Guo,Xiao-Chuan Wang,Wen-Zhong Lu,Wen Lei
The crystal structure and dielectric properties of Ti 4+ -substituted CaSnSiO 5 ceramic were investigated. Ti 4+ entirely substituted Sn 4+ of CaSnSiO 5 , and the solid solutions were formed at Ca(Sn 1- x Ti x )SiO 5 (0 ≤ x ≤ 1.0) ceramics. The evolutions of crystal structure were analysed through Rietveld refinement and transmission electron microscopy , and the phase transition from A 2/ a to P 2 1 / a space groups at Ca(Sn 1- x Ti x )SiO 5 (0.9 ≤ x ≤ 1.0) ceramics was clarified. The change in dielectric properties was related to the structural evolution of Ca(Sn 1- x Ti x )SiO 5 (0 ≤ x ≤ 1.0). The τ f values of Ca(Sn 1- x Ti x )SiO 5 (0 ≤ x ≤ 0.4) ceramics initially decreased to +49.8 ppm/°C and then increased to +98.3 ppm/°C because of Sn/TiO 6 octahedral distortion. The temperature coefficient of capacitance and ε r anomaly peak were controlled by Ti 4+ substitution for Sn 4+ at Ca(Sn 1- x Ti x )SiO 5 (0.4 ≤ x ≤ 1.0) ceramics. The results provided a way to control the τ f value of microwave dielectric ceramics .
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