【作者】 肖立华；

【导师】 苏玉长；

【作者基本信息】 中南大学 ， 材料物理与化学， 2013， 博士

【摘要】 摘要：节能减排已成为时代的主旋律。开发高性能窗用透明隔热材料备受人们的青睐。窗用透明隔热材料必须具有可见光高透明和近红外强吸收／反射屏蔽的光学特性。从理论和实验方面设计并研发新型窗用透明隔热节能材料已成为当今世界的重要研究课题。目前,研究者大都注重高透明隔热材料的制备和性能应用与开发的实验研究,而理论研究较少,非常有必要将理论和实验结合起来加快研究进程。本论文在理论方面采用基于密度泛函理论的第一原理方法计算了几种窗用透明隔热材料的电子结构,并预测了它们不同类型薄膜的光学性能。实验方面成功制备了稳定性较好的纳米LaB6/乙醇分散液,并探讨了其光学性能。研究内容和成果主要包括以下几点：1)采用第一原理方法研究了稀土六硼化物RB6(R＝Sc、Y和La)的几何、电子结构和光学性质。电子结构分析表明,这三种化合物均属于金属性导体材料,价带顶和导带底分别主要由B-2p态和金属原子R-nd(n=3,4,5)态构成,并随着金属R的原子半径和电子层数的增大,导带朝远离Fermi能级的方向移动。通过对三种稀土六硼化物RB6(R=Sc, Y和La)的介电函数、吸收光谱、反射率和能量损失光谱等光学常数的计算和分析,研究了三者的光学性质并对不同类型光学薄膜的光学性能进行了比较。结果表明：不同于ScB6,YB6和LaB6可用作高性能窗用透明隔热材料。发现LaB6的可见光高透明可归因于载流子电子集体振荡,也就是体等离子激元,而其近红外强吸收特性则可归因于等离子振荡的偶极子模式。该研究结果对这三种稀土六硼化物目前的应用开发和扩大其应用领域可提供很好的理论指导。2)通过对稀土六硼化物RB6(R=Ce, Pr, Nd, Sm, Eu, Gd, Er, Tm, Yb和Lu)电子结构及磁学和光学性质的计算,发现RB6(R=Ce, Pr, Nd, Sm, Eu, Gd, Er和Tm)属于铁磁材料,而YbB6和LuB6不具有磁性。电子结构分析表明,这十种稀土RB6的电子性能主要由稀土金属R决定。光学性质计算表明,它们均在低能红外区具有较强的反射性,并显示微弱的体等离子激元；除GdB6和LuB6外,稀土六硼化物RB6(R=Ce, Pr, Nd, Sm, Eu, Er, Tm和Yb)均不适合用作窗用透明隔热材料。3)对TiN的电子结构和光学性质的计算,发现TiN属于导体材料,其价带和导带分别主要由N-2p态构成和Ti-3d态构成。对其不同类型薄膜光学性能的计算结果表明：TiN薄膜具有可见光高透明和近红外强吸收/反射隔热节能的光学特性。4)采用第一原理方法对单斜相和金红石相VO2电子结构和介电函数、反射率、吸收光谱、能量损失光谱等光学常数进行了研究,结果表明：单斜相VO2不具有屏蔽近红外辐射的性能,而金红石相VO2适合用作窗用高透明隔热材料。5)以无水乙醇为分散介质,经过对纳米LaB6改性和分散,成功地制备了稳定性较好的纳米LaB6/乙醇分散液,进而研究了改性剂种类及用量、分散条件等对分散液稳定性的影响,并通过透射电子显微镜(TEM)、傅立叶红外光谱(FTIR)和激光散射粒度分析等表征方法调查了在无水乙醇中阴离子表面处理剂改性LaB6纳米粒子的机理,同时研究了纳米LaB6/乙醇分散液的光学性能。证实LaB6纳米粒子具有可见光高透明和近红外强吸收隔热的光学特性。更多还原

【Abstract】 Abstract:Energy-saving and emission reduction have become the theme of the Times. Transparent heat-insulating materials for windows with high performance are welcomed greatly. They must be characterized by high visible light transpancy and strong near-infrared rays absorption/reflection. Research on novel high transparent and heat-insulating materials for windows on theoretical and experimental basis has become an important research topic in today’s world. So far, most of researchers focus on the preparation and application of them, but there is very few theoretical study. It is necessary for researchers to accelerate the research process by combining theoretical studies and experimental designs. In this thesis, on the theoretical side, the electronic structure of several transparent and heat-insulating materials for windows were investigated using the first-principles method, and optical performance of different kinds of films made of these materials had been predicted in theory. Experimentally, nano-LaB6ethnol dispersion with excellent stability and dispersion was prepared, and its optical performance had been examined. The main research contents and achievements are listed as following:Firstly, the geometry, electronic structures and optical properties of rare earth hexaborides RB6(R=Sc, Y and La) were studied using the first-principle density function theory. The electronic structures of three compounds demonstrate that these compounds are all metallic conductor materials. The upmost valence bands and the bottommost conduction bands of RB6(R=Sc, Y and La) are mainly composed of B-2p states and metal R-nd(n=3,4,5) states, respectively. And as atomic radius and e-layer of metal R increase, conduction bands move away from the Fermi energy level. The optical properties of RB6(R=Sc, Y and La) were also investigated by calculating and analyzing their dielectric functions, absorption spectra, reflectivity and energy-loss spectra in details, and optical performance of their different films was analyzed theoretically. The results show that YB6and LaB6can be used as high transparent and heat-insulating materials with high performance for windows, but ScB6is not. That LaB6can be transparent to the visible light may be ascribed to a collective oscillation (volume plasmon) of carrier electrons and strong optical absorption for the near infrared (NIR) wavelength may be attributed to dipole mode of plasma oscillation. These findings provide theoretical data for the application of three rare earth hexaborides, and it is greatly important to extend their potential field of application.Secondly, the electronic structures, magnetic and optical properties of RB6(R=Ce, Pr, Nd, Sm, Eu, Gd, Er, Tm, Yb and Lu) had been investigated. The results show that RB6(R=Ce, Pr, Nd, Sm, Eu, Gd, Er and Tm) are all ferromagnetic materials, but YbB6and LuB6are non-ferromagnetic materials. The electronic properties of ten compounds RB6are determined mainly by metal R. Optical properties of them show that they all have high reflectivity in the low-energy infrared region and have weak volume plasmon. GdB6and LuB6are suitable for transparent and heat-insulating materials for windows, but RB6(R=Ce, Pr, Nd, Sm, Eu, Er, Tm and Yb) are not.Thirdly, the electronic structures and optical properties of TiN had been investigated. The calculations show that TiN is conductor. The valence bands and the conduction bands of TiN are mainly composed of N-2p states and Ti-3d states, respectively. The results of optical performance of TiN films indicate it has the character of high visible light transparency and strong absorbance/reflectivity in the near-infrared region.Fourthly, the electronic structures and optical properties such as dielectric function, absorption spectra, reflectivity and energy-loss spectra of monoclinic phase and rutile phase VO2had been studied. The calculated results indicate that monoclinic phase VO2has not the character of near-infrared radiation shielding. But rutile VO2is suitable for transparent and heat-insulating materials for windows.Finally, nano-LaB6/ethanol dispersion was prepared by surface modification and dispersion in ethanol medium. The influence of modifier type and amount, dispersing condition on the stability of nano- dispersion was studied. Nano-LaB6dispersion was characterized by TEM, FTIR and laser particle diameter analyzer, and the modification mechanism of nano-LaB6particles with anionic surfactants was discussed. Optical performance of nano-LaB6dispersion also had been studied. It confirms Nano-LaB6particles have the unique optical behavior of high visible light transparency and strong optical absorption for the NIR wavelength.更多还原