Yuh-Ruey Wang

Effect of glass composition on the densification and dielectric properties of BaTiO3 ceramics

An ongoing research goal of thick film capacitors and multilayer capacitors is to lower the firing temperature of the dielectrics. This paper presents the results of using three simple glass systems including PbO–B2O3, PbO–SiO2, and Bi2O3–B2O3 as sintering aids for hydrothermal synthesized BaTiO3. Glasses with different ratios of the modifier/glass former were employed. Effects of adding these glass systems on the BaTiO3 ceramics sintered at 850°C were investigated through measuring and analyzing the density, grain size and dielectric property. It was found that BaTiO3 sintered with glasses composed of 90 mol% PbO–10 mol% SiO2 or 90 mol% PbO–10 mol% B2O3 to 60 mol% PbO–40% B2O3 are helpful to reduce the firing temperature for typical thick film and MLCC applications. They possess high dielectric constant (≈1650) due to their high densification characteristics with the grain size of ≈0.7 μm. In addition, glasses composed of 90 mol% Bi2O3–10 mol% B2O3 to 40 mol% Bi2O3–60 mol% B2O3 are beneficial for thin dielectric layer applications, on account of the high sintering density and a small grain size of ≈0.1 μm with an acceptable K value.

Liquid phase sintering of NiCuZn ferrite and its magnetic properties

Abstract The influence of glass additives on the densification, microstructural evolution and magnetic properties of NiCuZn ferrites were investigated. Two glass systems including PbO·SiO 2 and PbO·B 2 O 3 were used to reduce the sintering temperature of a NiCuZn ferrite. The PbO·SiO 2 glass system was shown to be an effective additive to obstruct the grain boundary movement and prevent the abnormal grain growth. In addition, it significantly lowers the sintering temperature of the ferrite. Ferrites sintered with PbO·SiO 2 have higher resistivity, higher Q and higher H c compared with those of PbO·B 2 O 3 systems. These results also indicated that the ratio of modifier to glass-former did not significantly change the densification behavior, microstructural evolution and magnetic properties of the NiCuZn ferrite.

Effects of Additives on the Densification and Microwave Dielectric Properties of Binary CaO–B2O3–SiO2 Glass

Glass systems, consisting of binary CaO–B2O3–SiO2 (CBS) glass (referred to as glass AB) and various amounts of Li2CO3, TiO2, and Al2O3 additives, were prepared in this study. The effects of the additives on the densification and microwave dielectric properties of binary CBS glass were investigated. Binary glass AB was not densified until the sintering temperature reached 875 °C; however, with the addition of 1 wt % Li2CO3 (referred to as glass L1), the glass achieved a maximum density at 825 °C. The resultant glass-ceramics contained a major phase quartz, SiO2, and a minor phase, CaB2O4, and had a dielectric constant (er) varying from 4.10 to 4.23 and a minimum tan δ of 0.0015, as frequency increased from 4.3 to 18.6 GHz. For glass L1 with further addition of the ceramic filler Al2O3 (up to 30 wt %), the maximum densification was reached at 775 °C and the formation of CaB2O3 and SiO2 crystallites was suppressed. Both er and tan δ increased with the Al2O3 content of the glass-ceramics. Further addition of the crystallization agent TiO2 (up to 5 wt %) to glass L1 slightly reduced the sintering temperature to 800 °C. The X-ray diffraction (XRD) intensities of the quartz SiO2 and CaB2O4 crystallites as well as the er and tan δ values of the resultant glass-ceramic increased with the amount of TiO2 added.

Ba2Ti9O20 Thick Films Deposited by Novel Aerosol Deposition Method

In this study, microwave ceramic Ba2Ti9O20 thick films were successfully fabricated by aerosol deposition (AD) with carrier gases of oxygen and argon. Ba2Ti9O20 films with uniform thicknesses of 6 µm were obtained. The grain sizes of the films were ≈0.2 µm, which were much smaller than those of the starting Ba2Ti9O20 powders (≈1.3 µm), because the particles fractured to smaller fragments and deformed to fill the gaps between the deposited particles during impact with the substrate. The dielectric constant and dielectric loss of the Ba2Ti9O20 film prepared in argon (41 and 0.043, respectively) were larger than those of the Ba2Ti9O20 film prepared in oxygen (32.5 and 0.036, respectively), which was largely due to the formation of oxygen vacancies. The Ba2Ti9O20 films prepared remained fairly stable with respect to voltage and temperature variations.

Microstructure Evolution and Microwave Dielectric Properties of Multi-Phase Ba(Ti1-xMx)O3 Ceramics

In this study, the feasibility for use of multiphase BaTiO3 ceramics as microwave dielectric resonators was evaluated through the substitution of metal ions in B sites, such as ions of Mn, Co, Mg, In, Fe, Zn, and Ni. The effects of metal ions substitution and sintering conditions on the densification, microstructural evolution and microwave properties of the BaTiO3 ceramics containing cubic and hexagonal phase were examined.