Laser Rapid Synthesis Of La <sub> 2 </ Sub> (moo <sub> 4 </ Sub>) <sub> 3 </ Sub> And Ce <sub> 2 </ Sub> (wo <sub> 4 </ Sub>) <sub> 3 </ Sub> Materials And Their Thermal Expansion Stu

Negative thermal expansion (NTE) materials have received considerable attention during the past few years. The new types of negative thermal expansion oxide materials are saline of W, Mo, V and P, mainly including three series AM₂O₈, AM₂O₇ and A₂ (MO₄)₃ . Tungstate and molybdate family of A₂ (MO₄)3 have strong negative thermal expansion in a broad temperature range and the thermal expansion coefficient can be changed easily by adjusting the components. Some investigations indicate that the bigger the radius of A³⁺ cation is, the stronger the negative thermal expansion effect.At the present, molybdate and tungstate are generally synthesized by standard solid state reaction technique or co-precipitate method. But all above-mentioned methods have some unavoidable disadvantages, such as complication in synthesis procedures, time and energy over-costing, so that these methods are not suitsble for mass production. A novel rapid synthesis technology by laser sintering is proposed and demonstrated in this thesis with the aim to overcome the above-mentioned shortcoming of the existing methods.We drew upon big rare earth ions in this work. The samples of La₂(MoO₄)₃ and Ce₂(WO₄)₃ have been synthesized by the new fabricating method for the first time . The samples were analyzed by Raman spectroscopy, X-ray diffraction and SEM. It is shown that sample of La₂(MoO₄)₃ possesses compact structure and good figure. The raw material reacted completely and the sample is the same structure. The investigation of the specimen surface by a scanning electron microscope ( SEM ) and energy-dispersive spectrometer ( EDS ) shows that the surface is composed of small crystal conglomeration and the size of the crystal is about 30nm～50nm , in which the stoichiometric proportion of elements is same . La₂(MoO₄)₃ is indexed in tetragonal system with the cell parameters a=0.5468nm, c=1.1902nm at room temperature . The Ce₂(WO₄)₃ samples' figures are not good. It is indexed in monoclinic CaWO₄ (scheelite)-type structure with the cell parameters a=0.7830nm, b=1.1736nm, c=1.2037nm,β= 110.83°. The specimen surface is composed of small crystalconglomeration and there are lots of ramiform crystals inside. The orientation of crystal growth is close to the direction of laser irradiation. All of specimens are stable at room temperature.The laser sintering technique is effective in the experiment. It may open new opportunities for manufacturing other tungstate and molybdate. It is obviously that the new method improves efficiency and saves cost. The laser sintering technique can adapt to produce small quantity or large volumes of samples for scientific research or industrial applications.