Synthsis And Characterization Of Gallium Nitride, Magnesium Silicon Nitride

On the basis of comprehensive and thorough investigation of literatures concerning the developments of gallium nitride and magnesium silicon nitride nanomaterials synthesis and applications, this dissertation is dedicated to explore the low-temperature synthesis of nanomaterials such as gallium nitride and magnesium silicon nitride in autoclaves. Combining the experimental analysis results and the study of the related reports, some proper theories are refered to discuss the growth mechanism of as-prepared nanomaterials.The main research contents are as follows:1. Being a wide-band-gap semiconductor, GaN has recently attracted enormous attention because of its wide use in optical devices operating at blue and ultraviolet wavelengths and in high-temperature electronic devices. A facile reaction of Ga, Na and N2H42HC1 has been carried out for the preparation of GaN nanomaterials at 200℃. This temperature is much lower than that of traditional methods, and the yield of GaN reached 50% according to the amount of Ga, X-ray powder diffraction patterns indicated that the products are hexagonal-phase GaN with lattice constants a=3.181A and c=5.179 A, which are near the reported values (a=3.189A,c=5.186A,JCPDS,card No.50-0792).The TEM image shows that the size of the product is 30 nm on average.However, when NaN3 were added to the system of Ga, Na and N2H42HCl, the hexagonal-phase GaN could be prepared at 100℃, The x-ray powder diffraction pattern indicated that sample was mainly hexagonal-phase GaN with a small fraction of rocksalt-phase GaN at 400℃, which has a lattice constant a=4.14 A.2. Recently, magnesium silicon nitride(MgSiN2)has been widely studied owing toits attractive properties such as high hardness, reasonable strength, fracturetoughness, and high electrical resistance at room temperature. In this study, magnesium silicon nitride (MgSiN2) powder was synthesized by a solid state reaction between silicon, Mg powder and NaN3 in an autoclave in 350-500 ℃. The yield of the product is calculated to be about 90% according to the amount of Si. X-ray powder diffraction patterns indicated that the products are orthorhombic MgSiN2(cell parameters:a=5.260 A, b=6.463 A, and c=4.951 A). The results of scanning electron microscopy and transmission electron microscopy(TEM) observations indicate that the product mainly composed of nanocubes which have the average diameters in the range of 200-500nm. The high-resolution TEM image shows clearly resolved fringes separated by 0.40nm, which corresponds to the(110) d-spacing of the orthorhombic MgSiN2-The effects of different synthesis conditions on the final formation of MgSiN2 powder,such as the different ratios of the precursors, reaction temperature, and reaction time were also investigated.