Papers by Author: Yong Jun Gu

Abstract: Ba₂Ti₉O₂0 ceramics were prepared with different additives of B₂O₃ by liquid coating method and solid phase mix method. The sintering behavior, phase structure and dielectric properties of ceramics were investigated by X-ray diffraction, scanning electron microscopy and inductance-capacitance resistance analysis. The liquid coating method can reduce the amount of sintering aid and minimized the negative impact of sintering aid on dielectric properties. A ceramic composite which could be sintered well at 900°C for 3h and showed good dielectric properties of εr=42,tanδ=0.002 and TCF=-4ppm/°C（1MHz）was obtained when 1.0mol/l H₃BO₃ was added to the Ba₂Ti₉O₂₀ ceramic.

Abstract: AlN/epoxy (AlN/EP) composites were fabricated by casting method. The effects of the AlN content on microstructure, thermal conductivity and thermal expansion properties of composites were investigated. The results indicate that with the AlN content increasing, the thermal conductivity increase, while the coefficient of thermal expansion (CTE) decreases. When the volume fraction of AlN is 25%, the thermal conductivity is 0.507 W/m•K, which is about 2.5 times higher than that of the epoxy matrix, while the coefficient of thermal expansion is 53.7 ppm/°C. The thermal conductivity results obtained were also analyzed using the Maxwell-Eucken model to explain the effect of AlN fillers on the formation of thermal conductive networks.

Abstract: (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 (BZN) ceramic samples were prepared by solid state reaction, In order to reduce the sintering temperature of BZN ceramic we have used liquid coating technology to dope CuO by precursor solution of CuSO4. The sintering behavior, microstructures, phase structures, and dielectric properties were studied. The process reduces the amount of sintering aid and minimized the negative impact of sintering aid on dielectric properties. A ceramic composite which could be sintered well at 900°C and showed good dielectric properties of εr=161,tanδ=0.005 and TCF=-398ppm/°C（1MHz）was obtained when 0.5mol/l CuSO4 was added to the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 ceramic.

Abstract: ZnNb2O6 ceramics doped with V2O5 were prepared by conventional mixed solid method. The effects of V2O5 addition on the microstructure and the microwave dielectric properties of ZnNb2O6 ceramics were investigated systematically. The sintering temperature of ZnNb2O6 ceramics with 1.0wt.% V2O5 addition can be effectively reduced from 1150°C to 1050°C. The secondary phase ZnV2O6 was observed in sintered samples with V2O5 addition content higher than 1.0wt.%. For 0.3–3wt.%V2O5-doped ZnNb2O6 ceramics, The dielectric constants (εr) of densified samples were higher than that of undoped ZnNb2O6 ceramics. The temperature coefficient of resonant frequency (τf) were shifted toward zero direction with the increase of V2O5 addition, However, the dielectric loss (tanδ=1/Q) increased. The 1.0wt.% V2O5-doped ZnNb2O6 ceramics sintered at 1050°C for 3h have the optimum microwave dielectric properties: εr=28, tanδ=0.0006 and τf=-42.5 ppm/°C.

Abstract: The BCB (BaCu(B2O5)) powders were synthesized by solid state reaction method and its effects on the microstructures, the phase formation and the microwave dielectric properties of MCT (Mg0.95Ca0.05TiO3) ceramics were investigated. BaO and B2O3 first forms BaB2O4, and then BaB2O4 reacts with CuO forming BCB. The sintering temperature of MCT ceramics with as-synthesized BCB addition can be effectively lowered from 1450°C to 1100°C due to the liquid phase effect. The formation of second phase (MgTi2O5) was restrained. The 3wt% BCB-doped MCT ceramics sintered at 1100°C for 3h have optimum microwave dielectric properties of Kr=21.5, Q×f=28000GHz, and TCF=-3.3ppm/°C. Obviously, BCB could be a suitable sintering aid that improves densification and microwave dielectric properties of the MCT ceramics.

Abstract: BaO-Sm2O3-4TiO2 (abbreviated BST) ceramic powder was prepared by the conventional solid-state reaction method. The effects of doping ZnO-2B2O3-7SiO2 (abbreviated ZBS) glass by sol-gel method on the sintering behaviors, microstructure, phase composition and dielectric properties of BST ceramics were investigated. The experimental results reveal that the main phase of samples doped with ZBS glass is tungsten bronze structure type BaSm2Ti4O12 phase, a litter Sm2Ti2O7 phase is also observed. The sintering tenperature of BST ceramics is remarkably reduced from 1350°C to 1050°C and the good dielectric properties of εr=60.2，tanδ=0.004，τf=-7.9ppm/°C were obtained for BST ceramics doped with 6wt% ZBS glass by sol-gel method sintered at 1050°C for 3h.

Abstract: The sintering behavior and microwave dielectric properties of the 16CaO-9Li2O-12Sm2O3-63TiO2 (abbreviated CLST) ceramics doped by small amount of LBS (Li2O-B2O3-SiO2) glass were investigated in this paper. The adding of LBS glass improved the densification of the CLST ceramics and the sintering temperature of the CLST ceramics had been efficiently lowered to 1000°C. Especially, the 10wt.% LBS doped CLST sintered at 1000°C for 3h has optimum microwave dielectric properties of Kr=69, Q×f=2846GHz, and TCF=9.7ppm/°C, indicating that it could be a suitable candidate for LTCC applications.

Abstract: ZnS:Fe and ZnS:Fe/ZnS core-shell nanocrystals were synthesized by chemical precipitation method. It was found that the ZnS: Fe based nanocrystals possess zinc blende structure. Compared to ZnS: Fe nanocrystals, the intensity of the X-ray diffraction peaks of ZnS: Fe/ZnS nanocrystals reduced and these peaks moved to lower angles. TEM images show that ZnS: Fe based nanocrystals are spheroidal and the average particles size is about 3~4 nm. PL spectra of ZnS: Fe nanocrystals revealed several mission bands, ~406nm, ~444nm, ~416nm, However, PL spectra of ZnS: Fe/ZnS nanocrystals showed several mission bands, ~420nm, ~432nm, ~449nm.

Abstract: Abstract. BaBi₄Ti₄O₁₅ powder was synthesized by molten salt synthesis (MSS) method in NaCl-KCl and Na₂SO₄-K₂SO₄ fluxes. The phases of reaction products and the microstructures at different calcined temperatures were detected by X-ray diffraction (XRD) and scanning electron microscope (SEM). As a result, the flaky BaBi4Ti4O15 powder with anisotropy was synthesized by molten salt synthesis method in NaCl-KCl and Na₂SO₄-K₂SO₄ fluxes in the range of 850～1050°C. Compared with BaBi₄Ti₄O₁₅ powder synthesized in the sulfate flux, the anisotropy level of BaBi₄Ti₄O₁₅ powder which was synthesized in chloride flux increased, the average particle size(APS) of BaBi₄Ti₄O₁₅ powder synthesized in the chloride flux is slight larger than in the sulfate flux. The thickness of BaBi₄Ti₄O₁₅ powder was synthesized by molten salt synthesis method in the chloride flux decreased than in the sulfate.

Abstract: Anisotropic BaBi₄Ti₄O15 powder was synthesized by a molten salt synthesis (MSS) method in K₂SO₄-Na₂SO₄ flux and the effects of different process parameters such as calcining temperature, and ratio of salt to reactant (R) on the phase formation and morphology of anisotropic BaBi₄Ti₄O₁₅ particles were also investigated. The as-synthesized powder calcined at 850-950°C exhibits a single tetragonal BaBi₄Ti₄O₁₅ phase. The morphology of BaBi₄Ti₄O₁₅ powder could be adjusted by changing the synthesis conditions. The average particle size (APS) of BaBi₄Ti₄O₁₅ powder increased with R changing from 0.8 to 1.0, while it decreased with further increasing of R to 1.2. In addition, the APS increased with increasing calcining temperature and it showed an Arrhenius dependence on the temperature. The corresponding apparent activation energy for particle growth is 31.9kJ/mol for calcining temperature of 850-1000°C.