材料科学基础[清华大学]—3.ppt

材料科学基础Fundamental of Materials;§2.1 Space Lattice;;2. Classification of materials based on structure Regularity in atom arrangement —— periodic or not (amorphous);Crystalline: The materials atoms are arranged in a periodic fashion. Amorphous: The material’s atoms do not have a long-range order (0.1～1nm).;;;Ⅱ.Space lattice 1. Definition: Space lattice consists of an array of regularly arranged geometrical points, called lattice points. The (periodic) arrangement of these points describes the regularity of the arrangement of atoms in crystals.;; A lattice may be one , two, or three dimensional two dimensions;Three dimensions;Ⅲ.Unit cell and lattice constants Unit cell is the smallest unit of the lattice. The whole lattice can be obtained by infinitive repetition of the unit cell along it’s three edges. The space lattice is characterized by the size and shape of the unit cell.;;How to distinguish the size and shape of the deferent unit cell ? The six variables , which are described by lattice constants —— a , b , c ; α, β, γ;Lattice Constants;§2.2 Crystal System Lattice Types;Ⅰ.Seven crystal systems;Seven Crystal Systems;Ⅱ.14 types of Bravais lattices 1. Derivation of Bravais lattices Bravais lattices can be derived by adding points to the center of the body and/or external faces and deleting those lattices which are identical. ;7×4＝28 Delete the 14 types which are identical 28－14＝14;2. 14 types of Bravais lattice Tricl: simple (P) Monocl: simple (P). base-centered (C) Orthor: simple (P). body-centered (I). base-centered (C). face-centered (F) Tetr: simple (P). body-centered (I) Cubic: simple (P). body-centered (I). face-centered (F) Rhomb: simple (P). Hexagonal: simple (P).;;Crystal systems (7);Ⅲ.Primitive Cell For primitive cell, the volume is minimum ;Ⅳ. Complex Lattice The example of complex lattice;Examples and Discussions;P → C