Yue-Feng Tang

Structure and electrical properties of strontium barium niobate ceramics

Abstract SBN, x =0.25, 0.35, 0.50, 0.60 and 0.75 series of ceramics prepared by traditional sintering method have been studied systematically. The impact of composition and sintering temperature on structures, microstructures, and electrical properties of SBN ceramics was characterized of X-ray diffraction, scanning electron microscopy, and electrical measurements. It is found that the composition and temperature play an important role on the fabrication of single phase tetragonal TTB SBN ceramics. At x =0.5, TTB SBN ceramics can be obtained at 1200°C. For x 2 O 6 even at 1300°C; TTB structure SBN and orthorhombic phase SrNb 2 O 6 for x >0.5. The complete TTB phase is produced at 1350°C. With Sr content increasing, the electrical performances show a regular change, strongly conforming to the reducing of the Curie temperature. SBN with the Sr composition of x =0.60–0.75 is a promising candidate for electro-optics device applications.

Preparation of composite coating particles of α-Al2O3–SiO2 by heterogeneous nucleation-and-growth processing

In order to solve the difficult problem of heterogeneity of different components in the procedure of ceramic preparation, heterogeneous nucleation-and-growth processing is used to prepare the homogeneous distribution powders. Composite coating particles consisting of alpha alumina cores (average particle size 0.57 μm) with an outer amorphous silica layer are prepared by the heterogeneous nucleation-and-growth processing. The amorphous silica layer on cores is confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and zeta-potential measurement. Effects of silica content in composite coating particles versus concentration of tetraethylorthosilicate (TEOS), pH value, reaction time and reaction temperature are studied.

Preparation of core/shell structure of α-Al(OH)3-SiO2 by heterogeneous nucleation-and-growth processing

In order to solve the difficult problem of heterogeneity of different components in the procedure of ceramic preparation, a novel processing (heterogeneous nucleation-and-growth processing) was used to prepare homogeneous distribution powders. Composite coating particles consisting of alpha aluminum hydroxide (α-Al(OH)3) cores (average particle size 0.42 μm) with outer homogeneous amorphous silica layer are prepared by heterogeneous nucleation-and-growth processing. Effects of silica content in composite coating particles versus concentration of silicon tetraethoxide (TEOS), pH value, time and temperature are studied. The homogeneous amorphous silica layer on cores is confirmed by X-ray diffraction, transmission electron microscopy and zeta potential measurement.

Fabrication and characterization of tunable uniform octahedral nanoporous inorganic silica membranes by assembly under a direct electric field

A facile method is first reported to fabricate uniform octahedral nanoporous inorganic silica membranes with a highly ordered and rigid array structure. The size of these uniform membranes ranged from 23.2 to 154.7 nm. In order to improve the mechanical strength of membranes, calcination was necessary and could adjust the size of these membranes in a limited range. Pore size distributions were tested by the mercury intrusion method.

SYNTHESIS AND CHARACTERIZATION OF FERROELECTRIC NANOCRYSTAL POWDERS OF SrBi2Ta2O9 BY A POLYMERIZABLE COMPLEX METHOD

Ferroelectric nanocrystal powders of SrBi2Ta2O9 (SBT) have been first prepared by a polymerizable complex (PC) route. The bismuth powder, strontium carbonate, and water-soluble tantalum oxalate solution were used as starting materials. Thermal analyses (TGA and DSC), x-ray diffraction (XRD), transmission electron microscopy (TEM), and conventional BET method were explored to characterize the structure, morphology, and specific surface area of PC-derived SBT powders calcined at 500-850 °C. As control samples, SBT powders were also fabricated by metalorganic decomposition (MOD) method. The XRD and TEM results indicate that high pure and well crystalline powders can be obtained at 650 °C with a average size of 50 nm. The PC-derived powder has much larger surface area than MOD-derived powder. The BET value of PC and MOD powder at 750 °C for 2h is 6.7 and 1.5m2/g, respectively. The specific surface area of powder prepared by conventional solid-state reaction is quite low, typically less than 1.5m2/g. Therefore...

Fabrication of composite coating particles with mullite stoichiometric ratio by a novel processing

In order to solve the difficult problem of heterogeneity of different components in the procedure of ceramic preparation, a novel processing (heterogeneous nucleation-and-growth processing) was used to prepare homogeneous distribution powders. Composite homogeneous coating particles with mullite stoichiometric ratio (consisting of alpha alumina cores (average particle size 0.26 μm) with an outer homogeneous amorphous silica layer) were prepared by the heterogeneous nucleation-and- growth processing. Effects of silica content in composite coating particles versus concentration of tetraethylorthosilicate (TEOS), pH value, reaction time and reaction temperature were studied. The homogeneous amorphous silica layer on cores was confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and zeta potential measurement.

Improved electrochemical performance of LiNi0.8Co0.15Al0.05O2 with ultrathin and thickness-controlled TiO2 shell via atomic layer deposition technology

Atomic layer deposition (ALD) technology is used to deposit TiO2 coating on the nickel-rich material LiNi0.8Co0.15Al0.05O2. The ultrathin and thickness-controlled coating shell serves as a physical barrier which protects the structure of the core and thereby enhances the electrochemical performance of the coated material. Coating shells of TiO2 with different thicknesses corresponding to different ALD cycles are obtained and detected via transmission electron microscope (TEM) analysis. A TiO2-coated sample with 138 ALD cycles reveals optimal electrochemical performance in the voltage range of 2.8–4.5 V. After 100 cycles, discharge capacities of 171.36 and 154.69 mA h g−1 at room (25 °C) and elevated (55 °C) temperatures are observed, with higher cycle-ability of 90.21% and 73.21%, in comparison with those of 50.13% and 43.97% for pristine samples at the same temperatures. The improvements in electrochemical characterizations are ascribed to the stable structure and interface modified by the high-quality dense, ultrathin and amorphous ALD TiO2 coating layer, which can protect the cathode particles from hydrofluoric acid attack.

Fabrication of composite particles with core-shell structures by a novel processing

In order to solve the difficult problem of heterogeneity of different components in the procedure of ceramic preparation, novel processing (heterogeneous nucleation-and-growth processing) was used to prepare a homogeneous distribution of powders. Composite coated particles with core-shell structures were prepared by the heterogeneous nucleation-and-growth processing. The effects of silica content in composite coating particles versus concentration of tetraethylorthosilicate, pH value, reaction time and reaction temperature were studied. The amorphous silica shell on the cores was confirmed by X-ray diffraction, transmission electron microscopy and zeta potential measurement.

Preparation and characterization of ferroelectric inverse opal via a sol-gel process

Ferroelectric inverse opals are promising in making tunable photonic crystals. In this work, inverse opal photonic crystals of several ferroelectric materials such as (Pb1-xLax)(Zr1-yTiy)O3 (PLZT), SrxBa1-xNb2O6 (SBN) and PbTiO3 were prepared respectively by a sol-gel procedure. Synthetic opals of monodisperse submicrometer polystyrene (PS) spheres were used as the templates and precursor solutions were infiltrated into the interstices of the templates. The templates were removed by the following calcination process, which also realized the crystallization. Annealing process was optimized for each ferroelectric material. A scanning electron microscopy was used to observe the pattern of the inverse opals. XRD results proved that they were in desired ferroelectric phase respectively. The final samples were well ordered in all 3 dimensions within small domains. The average size of a single ordered domain in the SBN sample is about 20μm x 40μm. The size in PLZT and PbTiO3 samples is about 30μm x 50μm. Those domains distribute equably on an area of 2cm x 1cm on the substrates.