Papers by Keyword: Crystal Growth

Abstract: Tungsten (W) micro-/nanoparticles were synthesized by thermally treating tungstate-based inorganic-organic hybrid nanobelts with a lamellar structure or the mixture of WO3 nanoplates and C6H12O6 in an Ar flow at 1000-1200 oC for 2-6 h. Phase compositions and morphologies of the W particles obtained were characterized by powder X-ray diffraction and scanning electron microscope.

Abstract: We studied the optimization of 300mm CZ silicon crystal growth in 28 inch hot zone with axial magnetic field. The convex of melt-crystal interfaces toward to the crystal are observed in our simulations under different growth velocities (0.3mm/min, 0.5mm/min and 0.65mm/min). The convections in melt were illustrated under different growth rates and intensities of magnetic field. The growth rate of 0.5mm/min and axial magnetic fields intensity of 0.3T were recommended as an appropriate control condition.

Abstract: By adding ZrO₂ and Y₂O₃ powder blend into the thermit, large bulk Al₂O₃/ZrO₂ (Y₂O₃) eutectics were prepared by combustion synthesis under high gravity, and the influences of high gravity on microstructures, crystal growth and properties of the materials were also discussed. The XRD patterns showed that the introduction of high gravity field did not change phase constitution of the ceramics, and the ceramic matrix was mainly composed of α-Al₂O₃, t-ZrO₂ and m-ZrO₂. SEM images and EDS analyses showed that with increasing high gravity level, the morphologies of the ceramic microstructures transformed from the cellular eutectics to the rod-shaped colonies, and volume fraction and aspect ratio of the rod-shaped colonies increased while the rod-shaped colonies were refined; as the high-gravity field was larger than 200g, the microstructures of composite ceramics developed as the randomly-orientated rod-shaped colonies with a symmetrical triangular dispersion of tetragonal ZrO₂ fibers of 300nm in the average diameter. Relative density, hardness, flexural strength and fracture toughness simultaneously reached the highest values of 98.6%, 18.6GPa, 1248MPa and 15.6MPa·m^1/2 as the maximum high-gravity level of 250g was achieved. The increases of relative density and hardness of the ceramics with the high-gravity level are attributed to the acceleration of gas-escape from ceramic melts and the elimination of shrinkage cavity in the ceramics. The increase in fracture toughness results from the enhancement of the coupled toughening mechanisms while the increase in flexural strength comes from the refinement of the microstructures, the decrease of critical defect size and the achievement of high fracture toughness.

Abstract: Bi₄Si₃O₁₂ powders are prepared by template -hydrothermal used Bi₄Si₃O₁₂ as a template made by molten-salt method. The phase composition and morphological characteristics of BSO nanoparticles were analyzed and observed by X-ray diffraction and transmission scanning electron microscopy. The results show that with the salt content of 50wt%, calcination temperature 770°C, it can form a high purity Bi₄Si₃O₁₂ template. A single Bi₄Si₃O₁₂ phase can be obtained by template –hydrothermal, with template addition 30wt%, the reaction temperature 240°C, holding time for 24h, and prolonging the reaction time is conducive to Bi₄Si₃O₁₂ grain growth. The powders have a good dispersion, and size of particles is about 10μm or so, and show a columnar shape.

Abstract: In this paper, maleopimaric acid anhydride (MPA) has been synthesized by the Diels-Alder addition reaction between abietic acid and maleic anhydride. Single crystal X-ray diffraction analysis reveals that MPA crystallizes in the polar space group P2₁ and contains one MPA and one DMF (Dimethylformamide) molecule in the asymmetric unit. MPA is firstly found to be a new type of low-molecular-mass organic ferroelectric with the saturation spontaneous polarization (P_s) about 60.0-61.6 μC·cm^-2 for single crystal samples, which is close to that of typical inorganic ferroelectric materials. MPA·DMF also shows second-order NLO property, with the second harmonic generation (SHG) responses approximately 0.5 times that of urea.

Abstract: A high yield of ultralong SnO₂ nanowires is successfully achieved by a simple thermal evaporation of SnO powders under air ambient. The as-synthesized SnO₂ nanobelts are single crystals with rutile structure. A backgated triode device for high-current applications has been developed with beltlike SnO₂ field emitters. The devices have confirmed triode operation with low turn-on gate voltage (about 170 V) and stable electron emission with brightness of 30 cd/m².

Abstract: In this work, needlelike precipitated calcium carbonate (PCC) nanometer particles were synthesized by industrial carbonation route using EDTA as crystal control agent. The morphological characterization shows that the as-synthesized needlelike PCC particles have an average diameter of 52 nm and an aspect ratio of around 14:1. The results indicate that EDTA plays a crucial role in the formation of needlelike PCC nanometer particles. A possible mechanism for the formation of needlelike PCC particles assisted by the crystal control agent EDTA is also proposed.

Abstract: On the basis of the proposed analytical phase transformation model, a new modified numerical model is presented to evaluate grain density evolution with only basic kinetics parameters. The proposed model is applicable for phase transformation including random nucleation, growth and impingement under isothermal condition. A two-step fit of the current model to numerical calculation describes the grain density evolution and the transformation kinetics well. Compared with the KJMA model, the modified method is advantageous for application without considering complex and detail transformation process.

Abstract: Using Zn powder as the raw material, Tetrapod-like ZnO nanoneedles with controllable morphology and size were successfully prepared by chemical vapor deposition. A screen printed normal-gated triode with Tetrapod-like ZnO nanoneedles field emitters is demonstrated. Field emission measurements show that the Tetrapod-like ZnO nanoneedles FED triode devices posses a good field emission property. The turn-on voltage is 270V. An anode current of 2.75 mA and a gate current of 0.43 mA are extracted at a gate voltage of 600 V with a brightness of 2300 cd/m².

Abstract: Single crystals of Na0.44MnO2 (=Na4Mn9O18) have been synthesized by a flux method at 1173 K for the first time. The crystal structure of Na0.44MnO2 has been refined by single-crystal X-ray diffraction method. The framework structure consists of double and triple rutile-type chains of edge-sharing MnO6 octahedra and a single chain of edge-sharing MnO5. The Mn-O bond distance and bond valence analyses revealed the manganese valence Mn3+/Mn4+ ordering in the Na0.44MnO2 structure.