【作者】 宋庆功；

【导师】 姜恩永；

【作者基本信息】 天津大学 ， 材料物理与化学， 2007， 博士

【摘要】 六方和菱方固溶体材料具有许多潜在的应用价值,对其进行研究的目的在于探究其性质与结构的内在关系、预报新材料,为实际应用和技术研究提供理论性支撑。本文采用基于密度泛函理论的第一性原理方法、结合密度波理论,研究了六方和菱方固溶体材料的结构和性质,取得的代表性成果如下:用密度波理论研究确定了简单菱方晶格的7种有序结构类型,并预报了刚玉型阳离子有序固溶体的结构,得到已有实验结果的佐证。根据密度波理论建立晶胞模型,使用材料建模与模拟软件包Materials Studio 4.0,对有序LixTiS2,stage-2 LixTiS2,AgxTiS2和AgxTiTe2系列的结构和性质进行了研究。选用DFT-LDA方案,在0≤x≤1范围内,对这4个系列进行了几何结构优化和总能量计算。得到的每个系列的晶格参量协调性好、与实验结果吻合较好,特别是Li1/4TiS2系统的c0好于国际同类工作。研究了阶梯化对有序LixTiS2系统的影响。发现了其夹层间距的额外膨胀和压缩的互补关系,并给予物理解释。用形成能判断有序结构的稳定性,预报了stage-2有序Li1/4TiS2和有序Ag3/4TiTe2等晶体的结构类型。将离子导电性与形成能建立了定性的关系,预报了AgxTiS2的有序—无序相变温度和离子扩散活化能较高;LixTiS2的离子导电性较好,得到已有实验结果的佐证。选用DFT-GGA方案,研究了AgxTiTe2系列的光学性质。得到的反射光谱与实验结果吻合较好;吸收光谱表明,AgxTiTe2吸收太阳光能力较强、范围较宽,有可能成为新型光电子材料。更多还原

【Abstract】 Hexagonal and rhombohedral solid solution materials are candidates for many potential valuable applications. The studies on these materials aim at probing into the internal relation of properties and structures and predicting new materials, as well as providing theoretical supports for their actual applications and technical researches.We have completed the studies on the structures and properties of hexagonal and rhombohedral solid solution materials using the first principles method based on the density functional theory (DFT) combined with the concentration wave theory (CWT). The typical results of the dissertation are as follows:Using the CWT, we have determined 7 ordered structure types of simple rhombohedral lattice, and applied them to predict the structures of corundum type cation ordered solid solutions, which are supported by experimental results reported. For LixTiS2, stage-2 LixTiS2, AgxTiS2, and AgxTiTe2 series, we have constructed crystal cell models according to the CWT, and made studies on their structures and properties using materials modeling and simulating software package Materials Studio 4.0.In a range of 0≤x≤1, we have completed the geometry optimizations and total energy calculations for the 4 whole series with DFT-LDA scheme. For every series, the obtained lattice parameters assort well with each other and accord with experiment results, and especially, c0 of Li1/4TiS2 system is better than the results of analogous work in the literature. We have investigated the effects of intercalates staging in LixTiS2 systems, and found the complementary relation of the additional expansion and the compression of spacing between sandwiches, and presented reasonable explanations.Using formation energy to estimate the stability of ordered structures, we have predicted the structure types of stage-2 ordered Li1/4TiS2, ordered Ag3/4TiTe2, and other crystal systems. We have also proposed a qualitative relation of ionic conductivity and formation energy, and estimated that the order-disorder transition temperature and the ionic activation energy of AgxTiS2 are higher than those of LixTiS2, and the ionic conductivity of LixTiS2 is better than that of AgxTiS2, which are supported by experimental results reported.By virtue of DFT-GGA scheme, we have studied the optical properties of AgxTiTe2 series. The obtained reflectance spectra are in good accordance with the experimental results reported, and the absorption spectra show that AgxTiTe2 systems may be a new kind of photoelectronic materials for their good absorptive capacity for absorbing sunlight in a large range.更多还原