Authors: Xin Hua Zhu, Jian Min Zhu, Shun Hua Zhou, Zhi Guo Liu, Nai Ben Ming, Dietrich Hesse
Abstract: BaTiO3 (BT) nanoparticles were prepared by the hydrothermal technique using different starting materials and the microstructure examined by XRD, SEM, TEM and HRTEM. X-ray diffraction and electron diffraction patterns showed that the nanoparticles were the cubic BaTiO3 phase. The BT nanoparticles prepared from the starting materials of as-prepared titanium hydroxide and barium hydroxide have spherical grain morphology, an average size of 65 nm and a fairly narrow size distribution. A uniform diffraction contrast across each single grain is observed in the TEM images, and the clear lattice fringes (with d110 = 0.28 nm) observed in HRTEM images reveal that well-crystallized BT nanoparticles are synthesized by the hydrothermal method. The edges of the particles are very smooth, with no surface steps. BT nanoparticles with average grain size of 90 nm, synthesized using barium hydroxide and titanium dioxide as the starting materials, show surface facets. In this case a bimodal size distribution of large faceted and smaller particles is observed. Diffraction contrast variation across the particles caused by high strains within the particles is clearly observed. The high strains obviously stem from structural defects formed during hydrothermal synthesis, presumable in the form of lattice OH− ions and their compensation by cation vacancies. HRTEM images demonstrate that surface facets parallel to the (100) and (110) planes and small islands with 3 ~ 4 atomic layer thickness are frequently observed around the edge of the particles.
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Authors: Takashi Kubo, Masayuki Hogiri, Hiroshi Kagata, Atsushi Nakahira
Abstract: Nano-sized BaTiO3 powders with narrow size distribution and the high tetragonality were attempted to synthesize by the rotary-hydrothermal process in water system, using two kinds of commercial anatase-type TiO2 (ST21/ST01) with different particle size and Ba(OH)2. The rotary-hydrothermal syntheses were done with the rotary-speed of 20 revolutions per minute at 523 K for 24 h. Highly- and mono-dispersed BaTiO3 powders were successfully synthesized by applying the rotary-hydrothermal process. For rotary-hydrothermal synthesis, it was found that the average size, tetragonality, and quality of the BaTiO3 particle strongly depended on the particle size of the starting material. In the case of using ST01 as a starting material, BaTiO3 nano-powders mainly composed of coarse-faceted particles (average particle size = ca.100 nm) with the tetragonal phase and very little lattice defects were successfully synthesized.
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Abstract: YVO4:Eu3+ phosphors were prepared by microwave hydrothermal method in this work. YVO4:Eu3+ phosphors were probed by photoluminescence (PL), X-ray powder diffraction (XRD) and scanning electron microscope (SEM). The effects of different preparation conditions on the photoluminescence, the structure and the morphology of YVO4:Eu3+ phosphors were studied. The experiment results show that the pH value and the Eu3+ doping amount have some important effect on the photoluminescence and the morphology of YVO4:Eu3+phosphors.
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Authors: Ying Wang, Gao Yang Zhao, Li Yuan
Abstract: The crystalline phase and morphology of the products formed during the synthesis of yttrium oxide via the hydrothermal treatment yttrium nitrate were characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. Products with high OH/NO3 ratios are formed with the increasing of hydrothermal treatment. The crystalline phases are evolved from Y2(OH)5.14(NO3)0.86•H2O toY4O(OH)9(NO3) and finally Y(OH)3. The hydrothermal reaction conditions play an important role in the synthesis of the microstructures. Results show the particle size and final morphology of samples could be controlled by reaction temperature, reaction time, and OH- concentration. Sheets, hexagonal and needle-like Y2O3 powders are obtained with the hydrothermal treatment of yittrium nitrate at 180 oC to 200oC for 2-8 hours at pH 9-13.
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Authors: Bi Li, Li Yun Cao, Jian Feng Huang, Jian Peng Wu
Abstract: Nanostructured cobalt sulfide(CoS) can be widely used as high energy density batteries, supercapacitors, solar photovoltaic materials and catalysts due to its excellent electronical, optical, magnetic and catalytic performance. In order to synthesize CoS crystallites in a efficient route, a facile microwave hydrothermal process was developed by using cobalt nitrate hexahydrate and thioacetamide(TAA) as source materials. The phase compositions and morphologies of the crystallites were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The influences of microwave hydrothermal temperature and time on the phase, grain size and morphology of the CoS nanocrystallites were particularly investigated. Results show that CoS crystallites can be obtained at the hydrothermal temperature of 180 °C. The as-synthesized CoS nanocrystallites are hexagonal phase that with the grain size of 10~30 nm. With the increase of hydrothermal time, the increase in particle size and the (102)-oriented growth are obviously.
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