Sintering,crystallization and dielectric properties of CaO-B_2O_3-SiO_2 system glass ceramics

CaO-B203-SiO2 （CBS） glass powders are prepared by conventional glass melting method at different melting temperatures whose properties and microstructures are characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. It is found that there are SiO2 and some unknown phases in CBS glass melting liquid from 1 300 ℃ to 1 500 ℃ and the amount of these phases decreases with the increase of the melting temperature. The CBS glass melted at 1 450 ℃ could be sintered from 830 ℃ to 930 ℃ and the bulk densities of the samples are all higher than 2.4 g/cm^3. From the points of the properties and energy conservation, the melting temperature of 1 450 ℃ is the optimal melting temperature. The glass ceramic sintered at 850 ℃ exhibits better dielectric properties： er=6.33, tan6=2.2×10^-3 at 10 GHz, and the major phases of the samples are CaSiO3, CaB2O4 and SiO2.

Microstructure and microwave dielectric properties of lead borosilicate glass ceramics with Al_2O_3

The effects of Al2O3 addition on both the sintering behavior and microwave dielectric properties of PbO-B203-SiO2 glass ceramics were investigated by Fourier transform infrared spectroscope （FTIR）, differential thermal analysis （DTA）, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results show that with the increase of Al2O3 content the bands assigned to [SiO4] nearly disappear. Aluminum replaces silicon in the glass network, which is helpful for the formation of boron-oxygen rings. The increase of the transition temperature Tg and softening temperature Tf of PbO-B2O3-SiO2 glass ceramics leads to the increase of liquid phase precipitation temperature and promotes the structure stability in the glasses, and consequently contributes to the decreasing trend of crystallization. Densification and dielectric constants increase with the increase of Al2O3 content, but the dielectric loss is worsened. By contrast, the 3% （mass fraction） Al2O3-doped glass ceramics sintered at 725℃ have better properties of density p=2.72 g/cm3, dielectric constant Er=6.78, dielectric loss tan8=2.6×10^-3 （measured at 9.8 GHz）, which suggest that the glass ceramics can be applied in multilayer microwave devices requiring low sintering temperatures.

Microwave dielectric properties of Ca0.7Nd0.2TiO3 ceramic-filled CaO–B2O3–SiO2 glass for LTCC applications

The effects of the Ca0.7Nd0.2Ti O3 ceramic addition on the crystallization,densification,and dielectric properties of CaO–B2O3–SiO2–(Al2O3)glass(C1:CaO–B2O3–SiO2 glass and C1A03:CaO–B2O3–SiO2–Al2O3 glass)for low-temperature co-fired ceramic(LTCC)applications are investigated.The cristobalite phase crystallized from C1 glass was inhibited by adding Al2O3.During sintering,Ca0.7Nd0.2TiO3 ceramic reacted with CaO–B2O3–SiO2–(Al2O3)glass to form the sphene(CaTiSiO5)phase.The amount of sphene phase increases with increasing sintering temperature.By adding 50–60 wt%C1 or C1A03 glass,Ca0.7Nd0.2TiO3 can be densified at 850–900℃.The relative dielectric constants for Ca0.7Nd0.2TiO3 added with C1 and C1A03 glasses were all 20–23.Ca0.7Nd0.2TiO3 added with C1 glass exhibited a lower dielectric constant than C1A03 glass due to cristobalite phase formation.For Ca0.7Nd0.2TiO3 ceramics added with 50 wt%glass,the variation in Q×f value presented the same trend as the sphene formation amount variation.The best Q×f value of 2380 GHz was achieved for Ca0.7Nd0.2TiO3 ceramics added with 50 wt%C1A03 glass sintered at 900℃due to the dense structure and greater amount of sphene.Ca0.7Nd0.2TiO3 ceramics added with50 wt%C1A03 glass sintered at 900℃exhibited a dielectric constant of 22.8 and Q×f value of2380 GHz,which are suitable for microwave LTCC applications.