Papers by Author: Xin Tai Su

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Authors: Qing Zhi Yan, Li-Ying Zhao, Xin Tai Su, Wen Feng Zhang, Chang Chun Ge
Abstract: Barium titanate powder has been prepared using sol-gel auto-ignition synthesis process and was compared with two commercial high purity BaTiO3 powders prepared by precipitation from oxalate precursor and by hydrothermal synthesis. Characterization by x-ray fluorescence, XRD, field emission scanning electron microscopy, SEM and BET revealed significant difference, particularly in particle size and agglomerate structure, resulting in different microstructure and dielectric property. The sol-gel auto-ignition synthesis process yielded weakly agglomerated powder with average particle size of 50 nm. This property is favorable for sintering and dielectric property.
Authors: Y.L. Jiao, L. Xiao, M.H. Zheng, X.H. Ma, Xin Tai Su, Qing Zhi Yan
Abstract: GdBaCuO bulk superconductors from precursors of Gd123 and ultrafine Gd211 powder have been fabricated by melt-textured-growth method in air. The ultrafine Gd211 powder was synthesized by an improved Pechini method. It was found that the lower temperature of synthesizing ultrafine Gd211 powder, the higher peritectic reaction temperature of GdBaCuO bulk superconductors. Jc reaches 4.7×104 A/cm2 at 77 K and self-field for ultrafine Gd211 starting particles with 0.2μm in diameter, and higher compared to larger Gd211 starting particles fabricated by solid state reaction. However, a large secondary peak effect did not appeared at Jc-B curves. ,
Authors: X.H. Ma, Xin Tai Su, Qing Zhi Yan, Y.L. Jiao, L. Xiao, Chang Chun Ge
Abstract: This paper describes the details on synthesizing nanocrystalline Gd2BaCuO5 (Gd211) using low-temperature combustion synthesis(LCS). The morphology and structure of the powders are characterized by field emission scanning electron microscopy (FESEM) and XRD. The size of obtained powders by this method calcined at 800 C is about 100nm, which is much smaller than the powders synthesizing by conventional solid state route. Besides, the Gd211 powders synthesizing by LCS have a low calcination temperature with a high-purity. The microstructure of melt-textured samples is also observed by FESEM, the result shows that the size of Gd211 particles trapped in GdBa2Cu3O7 (Gd123) matrix could be refined by using ultrafine Gd211 powder as a precursor. The refined Gd211 particles with a good distribution resulted in the improvement of Jc values in this system.
Authors: Wen Feng Zhang, Qing Zhi Yan, Xin Tai Su, Chang Chun Ge
Abstract: The Nb and Co doped barium titanate was synthesized by sol-gel auto-ignition synthesis process (abbreviated SAS) and compared with the doped powder of the same composition prepared by conventional ball milling process. The phase structure, morphology of the two as-obtained powders and correlative dielectric properties of sintered BaTiO3-based ceramics were measured. The XRD analysis demonstrated that the SAS powder was the Ba(M0.047Ti0.953)O3(M=Nb, Co) solid solution based on BaTiO3; it further suggested that Nb and Co cations could replace the Ti ions and reach reciprocal balance of acceptors and donors during the decomposition step of the organic fuel by igniting the dried gel. TEM observation showed that the Ba(M0.047Ti0.953)O3(M=Nb, Co) particles were spherical with the size ranged from 30 to 110nm. Furthermore, it was found that the value of the Curie temperature of both the doped powders was being lowered in comparison with pure BaTiO3 (Tc≈128°C ); and the dielectric constant at room temperature of the SAS powder was 5840, which was much higher than that of the conventional ball milling doped powder(3013). It was attributed to the maximum homogeneous distribution of dopants in Ba-Ti initial solution at atomic level via the SAS process.
Authors: Xin Tai Su, Qing Zhi Yan, Chang Chun Ge
Abstract: Ba3(Ca1.18Nb1.82)O9-d (BCN18) powder was synthesized using a wet chemical method from mixtures of all water-soluble compounds including Ba, Ca and Nb-citrate. It has been found that NH4NO3 in the initial solutions plays an important role in controlling the enthalpy of low temperature combustion process as well as the gel decomposition temperature. Further steps include evaporating, drying and calcinating. The obtained gels were characterized by TG-DSC, and the powder was characterized with XRD, TEM and BET. The experimental results have indicated that the heating temperature was only 800°C for synthesizing the powder and the average particle size was only about 40-50 nm. Furthermore it was found that a pure BCN18 phase with complexperovskite structure was formed at 800°C, which was about 800°C lower than that of the traditional solid-reaction method. So it is more practical and more superior to the traditional solid-reaction method and the present wet-chemical method in alcohol salt system reported in literature.
Authors: Qing Zhi Yan, Xin Tai Su, Wen Feng Zhang, Chang Chun Ge
Abstract: Non-agglomerated nano-sized BaTiO3 powders were prepared by a 3 step decomposition of barium titanyl citric acid chelate derived from Ba(NO3)2-TiO(NO3)2-citric acid-NH4NO3 based complex compound system. The 1st step was the thermal treatment of chelate wet gel at 150°C for 40min to remove water and non-bridging hydroxyl groups and to form expanded gel intermediate. The 2nd step was the decomposition of the organic fuel by igniting expanded gel intermediate at 300°C. The 3rd step was the formation of the high purity BaTiO3 by calcining the decomposed powders at 700°C for 2 hours. The most expanded gel intermediate was found to be a decisive factor for the elimination of hard agglomerate. In addition, the initial oxidant/fuel molar ratio was shown to strongly influence the characteristics of the powders thus obtained. The optimum oxidant/fuel value was 3 for obtaining non-agglomerated pure BaTiO3 powders with a particle size of 50 nm. The agglomerate degree of BaTiO3 powders was determined by particle morphology and uniformity of the green compact microstructure observed by field emission scanning electron microscopy and scanning electron microscope.
Authors: Xin Tai Su, Qing Zhi Yan, Chang Chun Ge
Abstract: Ba3(Ca1.18Nb1.82)O9-δ (BCN18) is a novel complex perovskite structure proton conductor. Nanocrystalline BCN18 was synthesized by means of sol-gel method. The solid oxide electrolyte was prepared by using this powder, and its sintering behavior was studied. SEM and XRD were performed to demonstrate its sintering properties. Its electrical conductivity was systematically investigated at intermediate temperature (400~600°C).
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