Study Of Structure And Energy Levels Of Doped Inorganic Crystal Materials

Doping is one of the most important methods to modify the properties of inorganic crystals. Doped inorganic crystals have been widely used as electrode materials for Li-ion batteries, photocatalysts, diluted magnetic semiconductors, photorefractive materials and so on. Doping behavior of exotic ions entering the lattice determines the structure of doped crystals, and impurity energy levels determine functional properties of doped crystals. Therefore, in order to design materials more rationally, it is of great significance to understand and predict doping behaviors of ions in inorganic crystals and impurity energy levels of doped inorganic crystals. Electronegativity (EN) and chemical bonds are two effective tools reflecting the microscopic structure and determining the macroscopic properties of materials. From the viewpoint of EN and chemical bonds, this thesis studied the occupancy selectivity of ions and impurity energy levels of inorganic crystals.In this thesis, site selectivities of cations in inorganic crystals were studied. It was found that electrostatic effect and steric effect are two important factors determining the occupancy sites, which can be well reflected by EN and radius. The occupancy site can be predicted by comparing the combined deviation degree of EN and radius between the dopant and the substituted ion, and dopants prefer to occupy the site where the deviation degree is the least. Based on this method, occupancy sites of38frequently used cations in some inorganic crystals which have two or more cations were predicted, which agree well with the available experimental results. This method will serve as guidance for the understanding and predicting doping behaviors of cations in inorganic crystals.Impurity energy levels of doped inorganic crystals were also studied in this thesis. A quantitative relationship was established between impurity levels of transition metal ions in inorganic crystals and basic atomic or bond parameters such as EN and bond length. Based on this relationship, impurity levels of frequently used transition metal ions in rutile-TiO2, III-V and II-VI semiconductors and some perovskite ternary oxides are calculated, which are in accordance with available experimental values. This certified the rationality of the relationship, which revealed the physical origin determining impurity energy levels of inorganic crystals, and can serve as an effective tool to predict photocatalytic, ferromagnetic and photorefractive properties of materials.