材料化学全英文课件第7课课件.ppt

材料科学基础Fundamental of Materials Science Prof: Tian Min Bo Tel: E-mail: tmb@mail.tsinghua.edu.cn Department of Material Science and Engineering Tsinghua University. Beijing 100084 Lesson seven 2.9 Some Additional Terminology in Crystallography 2.9.1 Crystal structure of some elements According to the crystal structure, the elements of the periodic table can be sorted to three types: Type Ⅰ：with typical metallic structure——FCC，BCC，HCP Type Ⅲ：covalent bonding , obey 8－N rule ① N ＝ 4 Crystal structure of diamond ② N ＝ 5 1 2 3 4 Crystal structure of Sb Crystal structure of Se and Te ③ N ＝ 6 2.9.2 Allotropy and polymorphic transformations Same crystal has different crystallographic structure at different condition. Examples: BCC BCC FCC ② C , graphite , diamond , CNT ① Fe Graphite C60 molecule Carbon Nanotubes 2.9.3 Single crystal versus polycrystal 1. For single crystals there is only one type of structure with same orientation. Single crystals is characterized by anisotropy. 2. Polycrystal consists of a lot of grain, small single crystals, with same structure but different orientations. These small single crystals are called grains. The boundaries between them are called grain boundaries. Grain boundary