【作者】 张志刚；

【导师】 薛冬峰； 李克艳；

【作者基本信息】 大连理工大学 ， 化学工艺， 2010， 硕士

【摘要】 本论文从晶体化学键理论出发,利用简单径向力模型考查了杂质离子进入铌酸锂(LiNbO3)晶体后引起的局部晶格弛豫,在此基础上提出晶格能方法判断离子在LiNbO3晶体中的占位情况,进而研究不同杂质离子对LiNbO3晶体的光学吸收边及光折变性能的影响。由于杂质离子MV+与LiNbO3晶体中的Li+(或Nb5+)的离子半径有所差异,掺杂到晶体中后会导致局部晶格结构的畸变,从而影响晶体的宏观物理性质。我们从微观结构角度出发,将化学键假设成无质量的弹簧,通过成键原子的性质计算键的力常数,进而研究杂质离子周围局部范围内的弹性形变,根据弹性力学最小势能原理分析杂质离子的介入引起的与其相连的氧离子的位置变化。研究表明杂质离子在LiNbO3晶体中形成的M-O键键长是在其本征氧化物中的键长基础上略有偏移,而与基质晶体中的Li-O(或Nb-O)键键长相差很大。在确定掺杂LiNbO3晶体结构后,我们研究了杂质离子对改变晶体紫外光学吸收边的作用机理。晶格能反映了晶体中离子间结合力的大小,可以用来表征杂质离子掺杂到LiNbO3晶体后的晶格结构稳定性。我们通过金属氧化物MmOn热力学哈勃循环建立了晶格能与M-O键键价的关系式,从而比较杂质离子分别占据锂位和铌位时的晶格能变化,分析掺杂LiNbO3晶体的结构稳定性,判断杂质离子在晶体中的占位状况。研究表明抗光折变离子和稀土离子都优先占据锂格位,光折变离子在LiNbO3晶体占位方式不统一,我们的理论分析与已有实验结果有很好的一致性。根据杂质离子在LiNbO3晶体的占位方式和离子自身的性质,分析不同离子对晶体光折变性能的影响。更多还原

【Abstract】 In the formwork of chemical bonds, a simple radial force constant model is used to study the lattice relaxation produced upon doping metal ions to lithium niobate (LiNbO3) crystals. And then a lattice energy model is proposed to study the occupancy of dopants in the LiNbO3 crystal on the basis of establishing the impurity bond length relaxation. Finally, we investigate the effect of various dopants on the optical absorption and photorefractive properties of LiNbO3 crystal.The local distortions of LiNbO3 lattice is occur when the doping ions enter the LiNbO3 matrix due to the difference of the ionic radius between doping ion and Li+(or Nb5+), which will have an impact notably on the macroscopic properties of material. Considering the chemical bond as a spring without mass, we calculate its force constant according to the properties of bonding atoms, to analyze the elastic deformation around the dopant. And thus the displacement of O2- joined by doping ion in the LiNbO3 crystal can be evaluated by the principle of minimum potential energy in the theory of elasticity. It shows that the bond length of impurity in LiNbO3 matrix only slightly deviates from its nature one, but has large difference from that of Li-O or Nb-O. Based on above research, the rule of doping ions in the change of optical absorption of LiNbO3 crystal is discussed.The lattice energy which is related to the cohesion of the crystal can typify the structural stability of doped LiNbO3 crystal. It can be described as the function of bond valence considering the Born-Haber cycle for the formation of an ionic oxide MmOn. The dopant occupancy in the LiNbO3 matrix can be determined by comparing the deviation of its lattice energy in different locations at both Li+ and Nb5+ sites. It shows that the optical damage resistant dopants and rare earth ions preferentially occupy the Li sites, and there is no regular rule for the occupancy of photorefractive ions, which well agree with the experiment results. Considering the occupancy and properties of dopants, we analyze the influence of doping ions on the photorefractive properties of LiNbO3 crystal.更多还原