Liu Hanxing

Synthesis and dielectric properties of Ba3NaBiNb10O30 ceramics

A new niobate Ba3NaBiNb10O30 was synthesized by the solid state reaction. The reaction mixture was characterized by thermogravimetric and differential thermal analysis (TG-DTA), X-ray diffraction and dielectric constant measurements. The results show that Ba3NaBiNb10O30 has an orthorhombic tungsten bronze structure with space group Cmm2 and the unit cell parameters are a=1.7660(1) nm, a=1.7626(1) nm, c=0. 78621(6) nm, Z=4. Ba3NaBiNb10O30 undergoes two phase transitions at 200°C and 400°C, respectively.

Structure and electrochemical properties of LiMn2O4−xF x

LiMn2O4−xFx prepared by the sol-gel method has a perfect crystal formation. The crystal particle size of the material was medium and distributed uniformly. The substitution of F for O increased the specific capacity of the material at the cost of the cycleability. The explanation of this results is that the F decreases the valence of Mn, that is, more Mn3+ and less Mn4+ exist in the material. The increase of Mn3+ will improve the initial specific capacity and Mn3+ is the original reason for Jahn-Teller effect that caused the poor cycleability of the cathode material by the micro-distortion of the crystal structure. In addition, the expanded measurement of the crystal lattice is also the reason for the poor cycleability. Therefore, the results of F-substitution and cation-substitution are opposite. If the two methods are combined, they can compensate the inability each other and the satisfactory results may be obtained.

Preparation, characterization and dielectric properties of Ba6Mg0.67Nb9.33O30 ceramic

A new niobate Ba6Mg0.67Nb9.33O30 was synthesized in the BaO−MgO−Nb2O5 system by solid state reaction at 1350°C for 48 h. The structure and dielectric properties of Ba6Mg0.67Nb9.33O30 were determined by X-ray powder diffraction, scanning electron microscopy and dielectric measurements. The results show that Ba6Mg0.67Nb9.33O30 belongs to ferroelectric phase of filled tetragonal tungsten bronze structure at room temperature with unit cell parameters: a=1.26052(4) nm, c=0.40045(2) nm, space group P4bm, calculated density 5.707 g·cm−3. Ba6Mg0.67Nb9.33O30 belongs to relaxor ferroelectrics undergoing diffusive phase transition, and the transition temperature (Tc) is 30°C observed at 10 kHz. At room temperature, Ba6Mg0.67Nb9.33O30 ceramic has a high dielectric constant 850 at 1 MHz and a low dielectric loss of 0.0052.

Molten salt synthesis of Ba(Mg1/3 Nb2/3)O3 powder

The single-phase Ba(Mg1/3 Nb2/3)O3 (BMN) powder was successfully prepared by the KCl molten salt synthesis (MSS) method. The temperature for single-phase BMN powders by MSS was about 400°C lower than that by the solid-phase method. The average particle size (APS) was about 0.91 μm at 900°C and increased with increasing synthesis temperature. Based on the APS, the activation energy for particle growth in the MSS, whose value was 64.1 kJmol-1, was attained. The sinterability of the powder prepared by MSS method was better than that prepared by solid-phase method.The single-phase Ba(Mg1/3 Nb2/3)O3 (BMN) powder was successfully prepared by the KCl molten salt synthesis (MSS) method. The temperature for single-phase BMN powders by MSS was about 400°C lower than that by the solid-phase method. The average particle size (APS) was about 0.91 μm at 900°C and increased with increasing synthesis temperature. Based on the APS, the activation energy for particle growth in the MSS, whose value was 64.1 kJmol-1, was attained. The sinterability of the powder prepared by MSS method was better than that prepared by solid-phase method.

Synthesis and performance of LiMnO2 as cathodes for Li-ion batteries

Two structure types of LiMnO2 were synthesized by sol-gel method and ion-exchange method respectively. The results indicate that orthorhombic phase LiMnO2 is more stable than layered LiMnO2, o-LiMnO2 can be synthesized directly by sol-gel methods followed by heat-treated in argon, but layered LiMnO2 was obtained only by indirect methods such as ion-exchange method. In this paper, we first synthesized layered NaMnO2 by the sol-gel method, and then obtained layered LiMnO2 by the ion-exchange method. The phase, constitution, chemical composition, and images of the products were tested by XRD, AAS (atomic absorption spectroscopy) and SEM. The electrochemical performances of the two structural types of LiMnO2 are obviously different during the initial few cycles, but later they both have a good capacity-retaining ability. The capacity of layered structure LiMnO2 is higher than that of o-LiMnO2.

Synthesis and dielectric properties of New Niobate Ba5BiTi3Nb7O30

A new niobate Ba5BiTi3Nb7O30 was synthesized by the solid-state reaction. It was characterized by X-ray diffraction and dielectric constant measurements. The results show that Ba5BiTi3Nb7O30 is paraelectric at room temperature and belongs to tetragonal 4/mmm symmetry with unit cell parameters a=1.25020 nm, c=0.39704 nm. Ba5BiTi3Nb7O30 has only one phase transition, paraelectric to ferroelectric, below 0°C.

Synthesis and X-ray powder diffraction characterization of a new niobate crystal NaBa2Li0.6Nb4.8Zn0.2O15

A new niobate compound was synthesized for the first time in Na2O-BaO-Li2O-ZnO-Nb2O5system by solid state reaction. The new compound was studied by X-ray diffraction, electron probe, X-ray microanalysis, chemical analysis and SEM. The result of X-ray powder diffraction shows that NaBa2Li0.6Nb4.8Zn0.2O15belongs to orthorhombic tungsten bronze structure, with space group Pba2(32)and lattice parameters a = 12.6115(2)Å, b=12.4981(2)Å, C = 3.9479(3)Å.The X-ray powder diffraction lines of the compound were well indexed.

The Setting Chemistry of Glass Ionomer Cement

The setting chemistry of glass ionomer cement was investigated by using mechanical determination of compressive strength at predetermined intervals, and measurement of structure changes of corresponding fracture sample by means of IR spectra and differential scanning calorimetry (DSC). Zinc polycarboxylate cement was used as a comparison sample. The compressive strength of glass ionomer cement (GIC) increases with aging. IR spectra and DSC of corresponding fracture sample show the structure changes of the matrix and interface layer comprising of silica gel during the predetermined intervals studied, however, no significant changes occur in the zinc polycarxyolate cement. Hence the structure changes of the matrix and or interface layer are responsible for compressive strength increasing with aging. The structure changes include the crosslink density, the ratio of complex form to ionic form, the content ratio of Al-PAA to Ca-PAA, the forming and maturing process of the interface layer comprising of silica gel.

Synthesis and Microstructure of Partly-oriented Bismuth Layer Structure Ferroelectrics Ceramics SrBi4Ti4O15

SrBi4Ti4O15 powder was synthesized by conventional solid state synthesis (CS) and molten salt synthesis (MSS). MSS method can synthesize plate-like SrBi4Ti4O15 at lower temperature (900°C) than CS method. Plate-like form becomes more distinct when the synthesis temperature increases. This would help cause the grain orientation of the ceramics after sintering. The sintered samples of MSS had grain orientation at (0,0,10) plane. The degree of (0,0,10) grain orientation F was 62.1%. Hot pressing made (0,0,10) grain orientation more distinct (F=85.7%). The microstructures of the sintered samples were detected by SEM. Due to the grain orientation, the density of samples fabricated by MSS was lower than that of prepared by CS.

Relationship between Liquid Phase Content and the Orientation of PMNT Ceramics by TGG Method

The effects of glass frit on the sintering and electric properties of PMN-PT textured ceramics were investigated. The glass frits, including PbO, Bi2O3 and ZnO, were selected since liquid phase sintering lowered the PMN-PT sintering temperature. The piezoelectric properties of PMN-PT ceramics with glass frit addition are strongly dependent on the densification. The addition of glass frits into PMN-PT matrix reduced the sintering temperature to 1 100 °C instead of 1 150 °C for samples without glass. The piezoelectric coefficients (d33) of PMN-PT textured ceramics achieved 568 pc/N with 1 wt% excess PbO.