超高压条件下几种特殊硅酸盐的合成及其压力对其晶体结构调制作用的研究

There are at least three important applictions of high pressure techniques in basic and materials science: 1) to synthesize the novel materials not accessible by other techniques, 2) to transform a given material from one phase to another, and 3) to uncover a underlying systematic and critically test theoretical concepts. .Silicate, including ceram, refractory material, glass material, cement, concrete and hydrothermal synthesized silicate building material, is one of the three basic man-made material and act as an important role in our life. Our research mainly concentrated on the characterization and high-pressure and high temperature (HP-HT) synthesis of rare earth element (REE) disilicate, forsterite and REE silicate apatite. The disilicates, especially the REE disilicates REE2Si2O7, have been widely studied for their unique magnetic, electrical and optical properties and their applications to optimize the properties of ceramic. .Forsterite is a low-pressure phase of magnesium orthosilicate with chemical formula of Mg2SiO4. The large family of forsterite based minerals is the major component of the earth's upper mantle. The low-pressure phase olivine [(Mg1-xFex)2SiO4, x≈0.1] is the dominant phase in this family of minerals, which includes many other compounds and displays a surprising variety of chemical and physical properties. The variability of their properties should be mainly attributed to the Mg2SiO4 component, which is at the origin of several important phenomena of geophysical interest. On the other hand, forsterite has become the focus of much recent researches, because of the difficult of its crystal growth.Rare earth (RE)-based apatites have recently attracted considerable attention for their high oxide ion conductivities which make them potentially useful as electrolytes for intermediate-temperature solid oxide fuel cells. High quality single crystal of the forsterite (Mg2SiO4) has been synthesized for the first time, using a piston-cylinder high-pressure and high-temperature (HP-HT) apparatus and LECO HR-1B Geological & Mineralogical HP-HT research systems..Crystals of lutetium disilicate (Lu2Si2O7) have been synthesized at 4GPa and 1200?C, using a piston-cylinder type high-pressure apparatus.The crystal structures of the two enantiomers are based on helical chains of Lu cations linked by [Si2O7]6- groups, which are parallel to each other and possess the same chirality, being right-handed for structure 1 and left-handed for structure 2. More interesting is that we have directly observed the helical chain under high-resolution transmission electron microscopy (HRTEM)..In this application, silicates with apatite structure, helical structure, and meso-porous structure will be made-up.

在现代无机合成中，人们越来越广泛地运用超高压这一极端条件下的合成方法来实现常规条件下无法进行的合成，并且得到多种多样在一般条件下无法得到的新化合物、新物相与新物态以及新合成路线与方法。本课题拟在本项目申请者过去几年在高压硅酸盐研究领域所取得的原创性发现的基础上，在高温高压条件下继续开展具有重要科学意义和应用背景的镁橄榄石、具有磷灰石结构稀土硅酸盐、具有手性结构稀土焦硅酸盐和具有微孔结构微孔稀土硅酸盐等一系列具有特殊结构和特殊功能的硅酸盐材料的研究工作。通过这些研究必将对这些硅酸盐在高压条件下的合成规律、成键特点、高压对硅酸盐的结构调制作用、影响这些硅酸盐结构和性质的各种因素和这些硅酸盐在实际的应用等方面取得重要成果。本项目研究不仅具有重要学术意义，而且在实际中有着重要应用背景。本项目的研究领域涉及物理学、化学、晶体学、地球科学和材料科学等学科，是一个跨学科的研究课题。

稀土因其优良的光学、电学、磁学等物理性质，已被广泛的应用于生活中的各个方面。作为一种传统材料，硅酸盐的合成和应用研究一直是科研工作者研究的热点。而作为硅酸盐材料的新秀，具有规则孔道结构的硅酸盐化合物在近几十年的研究中也表现出许多优异的性质，并在催化、吸附等方面表现出巨大的应用潜力。将稀土元素独特的发光性质与微孔硅酸盐均一的孔道性质有机的结合在一起一直是人们感兴趣并不断探索的研究课题。微孔稀土硅酸盐的合成大多都是采用中温水热法在200°C以下的温度条件下合成的，反应容器为不锈钢反应釜。本项目通过Quickpress3.0活塞-圆筒式高压反应装置和HR-1B-2型LECO高温高压反应装置，尝试在更高的压力和温度条件下，对具有新颖结构的微孔稀土硅酸盐/锗酸盐化合物的合成进行研究。在0.5~1GPa压力范围，300~700°C温度范围内成功合成出了一系列结构新颖的稀土硅酸盐及锗酸盐化合物，并对它们的晶体结构和荧光性质进行了研究。