【作者】 李卿；

【导师】 张国平；

【作者基本信息】 华中师范大学 ， 无线电物理， 2011， 博士

【摘要】 透明陶瓷材料因其优良的光学性能和机械性能,成为新一代光电子材料的研究热点,对于国家安全和国民经济可持续发展具有重大战略意义。目前对于透明陶瓷光学性能研究主要集中在制备工艺及实验探索上,从物理机制上探讨透明陶瓷的光学性能的研究尚不深入,因此阻碍了透明陶瓷材料的发展和应用。透明陶瓷的透光性能不仅与材料本身的化学组成有关,还受到材料的显微结构的影响。本文对透明陶瓷的透光机理及影响因素进行了探讨,建立了光波在多晶陶瓷中与气孔、晶粒、晶界等显微结构单元之间相互作用关系的散射模型,通过研究显微结构对光学性能的影响规律来分析提高陶瓷透明度的方法。首先,本文阐述了光散射的基本理论,研究了针对球形的Mie散射理论和针对非球形的离散偶极子近似法。基于两种方法计算了长方体、椭球体和圆柱体三种不同形状粒子以及等体积球形粒子在不同尺度参数下的散射效率因子。通过分析结果得到了将非球形粒子作为球形处理的适用范围,为光散射理论在分析透明陶瓷的光学性能中的应用提供了基础。其次,针对立方晶系透明陶瓷的结构特点,分别对其中的气孔和晶界这两个主要的散射元建立了光散射模型。采用Mie理论计算研究了气孔率、气孔尺寸及气孔尺寸分布等因素对直线透过率的影响。基于球形核壳散射理论计算研究了晶界折射率、晶界厚度及晶粒尺寸对直线透过率的影响。结果表明,残余气孔是影响透明陶瓷透光性能的最大因素。气孔造成的散射随着气孔率的增大而增大,且在气孔尺寸与波长相接近时达到最大。同时,只有当晶界上存在第(?)相时晶界相才会造成散射,直线透过率随着晶界相与晶粒折射率差异的增大及晶界相含量的增加而减小。在制备过程中通过消除气孔降低气孔率,保持晶界与晶粒成分一致,降低晶界相的比例,使晶粒尺寸更小更均匀可有效提高立方晶系陶瓷的透光性能。再次,针对非立方晶系透明陶瓷的结构特点,以氧化铝陶瓷为研究对象,建立了单轴晶陶瓷双折射散射模型。基于Mie理论计算研究了晶粒尺寸及晶粒尺寸分布等因素对直线透过率的影响。同时,在瑞利-德拜近似散射理论的基础上,深入研究了各向异性晶粒取向的变化对直线透过率的影响。结果表明,制备晶粒尺寸更小更均匀的陶瓷,使晶粒定向排列可减小双折射散射的损失,提高非立方晶系陶瓷的透光性能。最后,针对复相透明陶瓷的结构特点,以两相陶瓷为研究对象,基于密集分布粒子的散射理论建立散射模型,采用干涉近似法研究了晶相含量和晶粒尺寸变化对陶瓷透光性能的影响。分析结果表明,在制备复相陶瓷时选取两相材料的配比各占50%时的透过率最高,并且只有控制晶粒尺寸在纳米范围,才能在整个波长范围内得到较好的透光性能。更多还原

【Abstract】 Transparent ceramics have recently attracted appreciable attention of research in optoelectronic material, because of their excellent optical performance and mechanical properties. Nowadays, researches for the optical properties of transparent ceramics are mainly on the experiment and processing technology, the absence of the physical mechanism study limited the development and applications of transparent ceramics.The transmission properties of polycrystalline transparent ceramics are influenced by the chemical composition and the microstructure of the material. The fundamental photophysical mechanism of transparent ceramics and the influencing factors on transmission properties were discussed in this paper. Models have been established to describe the effects of microstructure such as pores, grains and grain boundaries on the in-line transmission of transparent ceramics. The aim of this paper is to study correlations between microstructure contents and optical properties of transparent ceramics in order to find the ways leading to high transparency.Firstly, the basic scattering theory is illustrated; research has been done on the Mie theory and Discrete Dipole Approximation (DDA) method. The scattering efficiency factors of cuboid, ellipsoid and cylinder particles were calculated by using the DDA method under different size parameters, and compared with the results of the equivalent-volume spheres based on Mie theory. The qualifications of treating the non-spherical particles as sphere obtained as the foundation of analyzing the scattering in transparent ceramics.Secondly, the characteristics of transparent ceramics with cubic crystal structure were analyzed. Models have been established on the scattering of pores and grain boundaries. Effects of pores on transmission were studied using the Mie theory. The in-line transmissions were calculated as a function of pore size, width of distribution and porosity. Porosity has great impact as the transmission decreases with the increasing of porosity. The minimum of the transmissions were observed when the pore size close to the optical wavelength. The effects of grain boundary were evaluated by core-shell model. The results show that the grain boundary which has grain boundary phase causes scattering. The higher the difference between the refractive indexes of the grain and grain boundary is, the lower the transmission. The transmission is affected strongly by the amount of the grain boundary in the visible range. We can conclude that the elimination of residual pores and the preparation of grains with uniform size are essential to improve transparency of ceramics. Meanwhile, keep the compositions of both the grain and grain boundary same and reduce the amount of grain boundary phase are desired to eliminate the scattering of grain boundary in cubic ceramics. Thirdly, the characteristics of transparent ceramics with non-cubic crystal structure were analyzed. A light scattering model has been established for the birefringence of uniaxial crystal ceramic. Effects of grain size and size distribution on transmission were studied using the Mie theory. Then, the effect of orientation was discussed by the developed Rayleigh-Gans-Debye approximation. The results show that the transparency of non-cubic ceramics depends not only the maximum grain size but also on the preferential orientation of their texture.Finally, the characteristics of transparent composite ceramics were analyzed. A model has been established for the ceramics with two phase based on the scattering theory with high particle concentrations. Effects of phase fraction and grain size on transmission were studied using Interference Approximation. The results show that the transmission reaches the maximum with a phase volume ratio of 50:50. Furthermore, the composite ceramics exhibit excellent transmission in both the visible part and infrared part of spectrum only when controlling the grain size in nanometer range.更多还原