Papers by Author: Li Hua Li

Abstract: ZnS: Cu/Fe nanocrystals were synthesized by hydrothermal method with thioglycolic acid as a stabilizer. The phases, grain size and luminescent properties of the nanocrystals were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and fluorescence photometer respectively. The results showed that ZnS: Cu/Fe nanoparticles have a particle size about 7nm and possess a cubic zinc blende crystal structure. The luminous intensity of ZnS: Cu/Fe nanocrystals was strongly when they were reacted at 140°C for 12 hours.

Abstract: Er3+:ZnS quantum dots(QDs) were synthesized by hydrothermal process. The structure, morphology and luminescence properties were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. It was found that the Er3+:ZnS QDs are zinc blende structure with an average particle size of about 8 nm. In PL spectra, The broad peak of ZnS NCs located at 400nm was commonly assigned to sulfur vacancies. The intensity of exciting peak and emission peak at of Er3+:ZnS QDs decreased with doping concentration increasing.

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: (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: 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: Mn_(1-X)S:A_X/ZnS (A: Er, Dy) nanocrystals were synthesized by chemical precipitation method. X-ray diffraction analysis show that Mn_(1-X)S:A_X/ZnS nanocrystals were zincblende structure. The high-resolution transmission electron microscope images indicated that Mn_(1-X)S:A_X/ZnS nanocrystals show a spherical shape, and their average grain size is about 4 nm. Photoluminescence spectra of Mn_(1-X)S:A_X/ZnS nanocrystals revealed that there existed several major emission bands, ～417 nm, ~509 nm, ~580 nm, ~617nm and ~680 nm. Mn_(1-X)S:A_X/ZnS nanocrystals exhibited enhanced luminescence properties compared with the pure Mn_(1-X)S:A_X nanocrystals. The enhanced photoluminescence properties of Mn_(1-X)S:A_X/ZnS nanocrystals should be attributed to the effective suppression of nonradiative recombination by the surface-passivation layer.