【作者】 唐旭东；

【导师】 丁泽军；

【作者基本信息】 中国科学技术大学 ， 凝聚态物理， 2009， 博士

【摘要】 高压已经成为现代科学的一门重要的技术,在物理学、化学、材料科学、地球科学等领域中获得广泛的应用和发展。压力作为除温度外的一维条件,对物质的各种性质都存在着不同程度的影响。对物质作用的基本效应是减小分子间或原子间的距离,从而引起物质组成结构(晶体结构、分子结构、原子排列方式)的变化,进而造成材料的能带结构、电子排布、电子轨道结构、电子态密度等性质的一系列变化。同时,高压或高温高压又是一种非常有效的合成各种功能材料的手段。因此,对高压下材料的物性的研究就显得非常重要。本文对几种有机芳香族共轭化合物包括苯乙酮连氮、反式联苯乙稀酮、苄连氮和无机化合物钕掺杂的钒酸钇晶体的高压下的物性进行了研究。本文共包含以下七章:第一章,简要介绍了高压技术及研究方法的发展,回顾了几种高压效应及相关领域的研究进展。着重介绍了金刚石对顶砧技术,相关的传压介质以及压力的定标。第二章,对有机分晶体和稀土离子发光作了介绍,综述了有机分晶体和稀土离子发光在高压下的物性研究。最后介绍了本文的设计思想。第三章,对苯乙酮连氮运用高压拉曼和高压荧光谱技术进行了研究,实验最高压力为17.7GPa。苯乙酮连氮分子晶体在高压下经历了两次晶体-晶体的结构相变,相变压力分别为3.6和5.8GPa。在压力超过8.7GPa后,反映晶格振动的拉曼模以及C-H振动模弱化消失,表明苯乙酮连氮分子晶体发生了晶体到非晶化的转变,完全非晶化的压力为12.1 GPa。这种非晶化状态并不稳定,高压诱导的聚合反应接着发生了。卸压以后,样品没有恢复到初始的结构形态,聚合生成物的状态特征在常温常压下依然保持稳定。苯乙酮连氮分子晶体在12GPa以上发生压力诱导的化学反应暗示着这种类型的化合物或许包含具有深远意义的未知变化。第四章,在常温下对反式联苯乙烯酮进行了高压原位拉曼、荧光光谱以及高压能量色散XRD研究。在压力大约为1.0-1.3GPa时,反式联苯乙烯酮发生了晶体-晶体的结构相变,同时有固相化学反应发生,反应完成的压力为6.5GPa。在EDXRD散射谱中有新的共价键类型的散射峰出现,推测为这次固相化学反应所致。可能的化学反应途径可能是分子中碳碳双键(C=C)的断开,相邻的分子之间再相互结合形成新的聚合分子。在压力为11GPa时,新产生的物质有结构相变发生。卸压以后,新的物质特征在常温常压下依然保持稳定。第五章,在常温下对钕掺杂的钒酸钇晶体进行了高压原位拉曼和荧光光谱研究,最高压力为10.88 GPa。研究发现,压力对钕掺杂的钒酸钇晶体的发光强度和跃迁能级有显著的调节效应。从常压到大约7.5GPa过程中,钕掺杂的钒酸钇晶体的发光强度逐渐减弱,荧光峰位向着长波方向移动。压力超过7.5 GPa后,发光强度急剧减小,峰位红移速率明显变慢。表明7.5GPa对钕掺杂的钒酸钇晶体是一个临界压力点,在这一压力下晶体发生了结构相变,晶体场也随之发生了突然的转变。新的光谱特征在卸压后依然存在,表明这次结构相变是不可逆的。第六章,在常温下对有机芳香族共轭化合物苄连氮分子晶体进行了原位高压拉曼和高压能量色散XDR研究。高压拉曼和高压能量色散XDR实验的最高压力分别为17.8GPa和15.1 GPa。研究发现苄连氮分子晶体在压力大约为2.2GPa和6.5 GPa时分别发生了晶体-晶体的结构转变。在12 GPa以上,根据反映晶格的外部振动模和C-H振动模的弱化消失判断苄连氮分子晶体发生了晶体-非晶体的结构转变。高压下的非晶态苄连氮并不稳定,在压力的作用下发生了固相化学聚合反应。卸压以后,这种新的聚合物可以存在于常压状态,初始的结构形态无法再恢复。可能的化学反应途径同前面的有机化合物一样,仍然是分子中碳碳双键(C=C)的断开,相邻的分子之间再相互结合形成新的聚合分子。第七章,对上述各章内容作了总结。更多还原

【Abstract】 High pressure technique plays an important role in modern science and technology, with impressive development and broad applications in many fields like physics, chemistry, materials and earth science. As another effect other than temperature, pressure exhibits its strength on changing properties of materials to a large extent. The distinct effect it brings is to reduce the distance between molecules or atoms of the materials, which results in the variation of its structure and composition （crystal structure, molecular structure, the alignment of atoms）, and further a series of changes happen, such as the energy band structure, the combination, orbital configuration and density of states of electrons. Meanwhile, high pressure （or together with high temperature） can be a highly effective method of synthesizing materials towards various purpose. For those reasons above, investigations of physical properties under high pressure is of great importance and thus highlighted. In this thesis, we present our work as follows. The pressure effects on physical properties of several kinds of organic aromatic conjugated compounds included Acetophenone azine, Trans,trans-Dibenzylideneacetone, Benzalazine and the inorganic material Nd:YVO₄ crystals are studied. The thesis consists of seven chapters.In Chapter One, we present a brief introduction to the development of high pressure techniques and methods and emphasis on technique of diamond anvil cell and the relative pressure transmitting medium and pressure calibrations.The second Chapter is an introduction to organic molecules and rare earth complex. We mainly summarize studies of physical properties under high pressure for organic molecules and rare earth complex. Finally we explained the outline of this thesis.In Chapter Three,we reported the high pressure study of acetophenone azine （APA）. High pressure Raman spectra of acetophenone azine have been measured up to 17.7 GPa with a diamond anvil cell. Two crystalline-to-crystalline phase transformations are found at pressures about 3.6 and 5.8 GPa. A disappearance of external modes and the C-H vibration at pressures higher than 8.7 GPa suggests that the sample undergoes a phase transition to amorphous or orientationally disordered （plastic） state, and the amorphization was completed at about 12.1 GPa. The disordered state is unstable and, then, a polymerization transformation reaction occurs with a further pressure increase. After the pressure has been released, the polymerization state can remain at the ambient condition, indicating that the virgin crystalline state is not recovered. The results show that the phenomenon underlying the pressure induced phase transition of APA may involve profound changes in the coordination environments of the symmetric aromatic azine.In Chapter Four, the trans,trans-Dibenzylideneacetone molecular crystal has been studied with high pressure Raman, fluorescence spectroscopy and EDXRD at room temperature. A crystalline to crystalline phase transition is found at pressure about 1.0-1.3 GPa; meanwhile, a pressure induced chemical reaction occurs and the reaction is completed at pressure about 6.5 GPa.The EDXRD spectra show that a new covalent bond may be produced in this chemical reaction process. The possible chemical reaction paths are suggested as the openning of C=C bond of the molecule and then combination between adjacent molecules. Another crystalline to crystalline phase transition may occur at pressure about 11 GPa. After the pressure has been released, the newly formed material can remain stable at ambient condition.In Chapter Five, Pressure-induced changes of the fluorescence spectra of Nd:YVO₄ crystals have been studied up to 10.88 GPa using a diamond anvil cell at ambient temperature. The changes of spectra indicate that pressure has remarkably influenced both the fluorescence intensity and the energy levels of Nd:YVO₄ crystals. With pressure increasing up to 7.5 GPa, the intensity of the spectra decreases and the peak positions shift red gradually. For pressure above 7.5 GPa, the fluorescence intensity decreases quickly and the shift rates of the peaks is slowed down. This suggests that 7.5 GPa is a critical point of the pressure at which the crystal may have a pressure-induced phase transition and the crystal-field changes. The new characters of the fluorescence spectra remain stable as the pressure is released to ambient pressure.In Chapter Six, we reported the high pressure study of benzalazine. High pressure Raman spectra of benzalazine have been measured up to 17.8 GPa and EDXRD up to 15.1 GPa with a diamond anvil cell at room temperature. Two crystalline-to-crystalline phase transformations are found at pressures about 2.2 and 6.5 GPa. A disappearance of external modes and the C-H vibration at pressures higher than 12 GPa suggests that the sample undergoes a phase transition to amorphous or orientationally disordered （plastic） state. The disordered state is unstable and, then, a polymerization transformation reaction occurs with pressure increasing above 12 GPa. After the pressure has been released, the polymerization state can remain at the ambient condition, indicating that the virgin crystalline state is not recovered. The possible chemical reaction paths are suggested as the openning of C=C bond of the molecule and then combination between adjacent molecules.In Chapter Seven, we summarize the contents of six chapters above.更多还原