High-Performance Ceramics VIII

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Authors: Hui Zhang, Xiao Hui Wang, Zheng Bo Shen, Ya Nan Hao
Abstract: Nanocrystalline BaTiO3 powder was directly synthesized by a convenient one-step solvothermal route. 8~10 nm BaTiO3 with different Ba/Ti ratios are obtained by adjusting the raw material ratios. The optimum raw material ratio of Ba/Ti is obtained. And the as-prepared BaTiO3 nanoparticles are all small and uniform. Influence of the nominal Ba/Ti ratios on diameter of nanocrystalline BaTiO3 powder was investigated by XRD, TEM and XRF analyses. It was found that the Ba/Ti ratios of the raw materials have a great influence on the process of powder fabrication. When the raw material Ba/Ti ratio is low (<0.9), the reaction cannot be finished and strong BaCO3 peaks were founded as the alkalinity of the system at the later reaction stage is too low. Besides, the Ba/Ti ratio of the product rises as the raw material Ba/Ti ratio increases.
Authors: Xiang Ning Feng, Wei Zhao, Hong Xing Wang, Wang Yang Jiang, Qin Li
Abstract: Spherical bismuth titanate (Bi4Ti3O12) particles were synthesized by hydrothermal method using Bi(OH)3, Ti(SO4)2 and KOH as raw materials, using polyvinylpyrrolidone (PVP) as the surfactant. The effects of concentration of the alkali solution, the reaction temperature and soaking time on the bismuth titanate crystal structure and morphology have been analyzed. XRD, SEM were used to characterize the crystal structure and microstructure of the as-prepared Bi4Ti3O12.The results show that the temperature plays an important role on the morphology of the Bi4Ti3O12.As the increase of the hydrothermal temperature, the Bi4Ti3O12 has been transformed from the spherical morphology to fibrous morphology. The spherical Bi4Ti3O12 powders with uniform distribution can be obtained when the concentration of KOH is from 1mol/L to 2 mol/L,the reaction temperature and hydrothermal time are 160°C and 24h respectively. SEM observation showed that the diameter of spherical Bi4Ti3O12 is about 500 nm.
Authors: Xiu Li Feng, Xiao Jiang Liu, Yong Qiang Yuan
Abstract: A new method to synthesize AgCoO2 delafossite powder with AgNO3 and LiCoO2 by the cation exchange solid state reaction at an atmospheric press has been presented. The effect factors such as moral ratio Ag/Li, reaction time, reaction temperature on the production were discussed systematically and the optimized preparation conditions were obtained. The crystal structure of AgCoO2 from XRD is monoclinic. SEM images showed that AgCoO2 is sheet in shape,single particle size is about 100nm and many single particles swam to form irregular polygon agglomerates.
Authors: Wei Xia Dong, Gao Ling Zhao, Xing Yong Gu, Bin Song, Gao Rong Han
Abstract: A novel CaTi2O4(OH)2 nanosheet was synthesized using anhydrous calcium chloride, lithium chloride and butyl titanate as the basic raw material by a template-free and surfactant-free hydrothermal method. The crystal structure, morphology and element synthesis were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) equipped with an EDS system. Effects of pH on the structure, morphology and electrochemical properties were investigated. The results showed that when pH was 6.7, CaTi2O5 phase was obtained. When pH was 8.3, pure CaTi2O4(OH)2 nanosheets were obtained. Further increasing pH to 8.6, CaTi2O4(OH)2 was obtained, however, and CaTiO3 phase also appeared. When pH was 8.3, the rate capacity of CaTi2O4(OH)2 nanosheets was further higher than those of the samples prepared for pH=6.7 and pH=8.6. It indicated that CaTi2O4(OH)2 nanosheets were helpful for lithium insertion and de-intercalation. The sample synthesized at pH=8.3 showed the best electrochemical performances, with first discharge specific capacity of 177.9 mAh/g at 0.1C rate. The CaTi2O4(OH)2 nanosheets might represent an opportunity for the applications in lithium ion battery.
Authors: Lin Qiang Gao, Hai Yan Chen, Zhen Wang, Xin Zou
Abstract: Nanoscale LiTaO3 powders with perovskite structure were synthesized using the solvothermal technique with glycol as solvent at 240°C for 12h. The powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). XRD was used to elucidate room temperature structures using Rietveld refinement. The powders were pure single pervoskite phase with high crystallinity. FESEM and TEM were used to determine particle size and morphology. The average LiTaO3 grain size was estimated to be < 200nm, and TEM images indicated that LiTaO3 particles had a brick-like morphology. In addition, the effect of the temperature on the LiTaO3 power characterisitics was also detailed studied.
Authors: Xing Ao Li, Wei Wei Mao, Xing Fu Wang, Xi Wang Wang, Yong Tao Li, Tao Yang, Jian Ping Yang
Abstract: Multiferroic BiFeO3 nanoparticles have been prepared by solgel method. The effects of single-substituted and co-substituted on the structures and magnetism of all the samples are investigated systematically. X-ray diffraction and Raman spectra results confirm that the samples simulate from a distorted rhombohedral structure to a cubic structure. Surface morphology of the samples were examined by scanning electron microscope (SEM). The ferroelectric and magnetic hysteresis loops shows coexistence of magnetism and ferroelectricity in the room temperature. The structure transition may be the main cause for the origin of improved magnetic and ferroelectric properties.
Authors: Wei Liang Liu, Xiao Jun Zeng, Shuo Qi Liu, Yan Feng Zhu, An Hua Wu
Abstract: The LaFeO3 polycrystalline feed rod was prepared by sintering La2O3 and Fe2O3 powder at 1400 °C for 24 h. The LaFeO3 crystal was grown by the floating zone method. The crystal preferred to crystallize along <100> direction. The X-ray rocking curve of the (100) crystal plane has a FWHM of 26 arcsec, confirming the high crystal quality of the sample. Some voids were observed on the polished surface. The thermal properties of LaFeO3 crystal during 298~773 K were tested. The specific heat of LaFeO3 crystal variation range was 0.58~0.76 J/(g·K), The thermal diffusivity of LaFeO3 crystal variation range was 3.47~0.85 mm2/s, The thermal conductivity of LaFeO3 crystal variation range was 13.10~4.21 W/(m·K).
Authors: Nan Wu, Xiao Dong Li, Shao Hong Liu, Yu Dong, Ji Guang Li, Xu Dong Sun
Abstract: Trivalent thulium ions (Tm3+) doped GdAlO3 (Gd1-xTmxAlO3) phosphors which show a blue luminescence of high color purity have been synthesized by using solid-state reaction method starting from nanosized powders. X-ray diffraction (XRD) measurements were used to analyze the phase transformations that take place during the preparation of the phosphors. The morphologies of the powders calcined at different temperatures were studied by using scanning electron microscopy (SEM). The luminescence properties of the compounds were investigated. Pure phase of orthorhombic type GdAlO3 (GAP) was yielded by calcining the phosphors at 1200°C for 8 h. The PL spectra showed representative Tm3+ emission. The strong band centered at ~488 nm and the weak one centered at 697 nm were attributed to the 1D2-3F4 and 1G4-3F4 transitions of Tm3+, respectively. The quenching concentration of Tm3+ was estimated to be ~0.75at.% (x=0.0075), for which can be ascribed to the exchange interactions. The decay curve was fitted to be a single exponent and the estimated fluorescent lifetime of the GdAlO3:Tm3+ phosphor was 1.73±0.08 ms.
Authors: Hong Ying Yu, Zhi Jiang Dong, Zhi Qin Chen, Shan Shan Luo
Abstract: In this paper, nanocrystalline ZnO particles were prepared feasibly by microwave assisted hydrothermal method with Zinc nitrate and NaOH as start materials. XRD results show the ZnO was crystallized well. The as-received powders are hexagonal platelets of about 20-100 nm in diameter. Toxicity experiments using wastewater microalgae (Chlorella sp.) revealed that the toxicity of ZnO is strongly related with the Zinc ions concentration in water.

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