[必威体育精装版]材料科学基础英文版课件.pptVIP

Chapter 1 Fundamental Concepts of Crystal;;People realized that there are two kinds of mineral in nature: Crystal and Amorphous. Are there some commonness for crystals? Regular external shapes, flat-geometric face The crystal firstly found was quartz with regular shape. Quartz with geometrical polyhedron shape was called as crystal.;Later, all solids with geometrical polyhedron shape were defined crystal, such as salt, calcite, magnetite.;Salt;The building blocks of these two are identical, but different crystal faces are developed;The external appearance of crystals are all characterized by flat bounding planes which intersect at characteristic angles. ;* ;2) Space Lattice and Equivalent Points;Equivalent Points, Space Lattice;Lattice;Lattice: Periodic repeating array;Lattice, Basis, Crystal Structure;Differences of Lattice and Crystal Structure;3) Lattice Elements 空间点阵的要素;（3）Nets 面网;（4）Space Lattice 空间格子;4) Properties of Crystals;1-2.Symmetry of Crystals;2) Point Symmetry;Symmetry;3) Symmetry Operations Symmetry Elements;（2）Symmetry elements;4) Symmetry Elements of Crystals;* ;Rotation Axis (Ln / n) —— Rotate;Representation of Rotation Axis ;That is not to say that molecules which have pentagonal symmetry, n=5, cannot exist in the crystalline state. They can, but their fivefold symmetry cannot be exhibited by the crystal as a whole. As shown in the figure, where a fruitless attempt has been made to pack pentagons to form a complete layer; thus, individual pentagons have fivefold symmetry but the array of pentagons does not.;;Inversion Axis;The onefold inversion axis is not a separate symmetry element, but is simply equivalent to the center of symmetry; also, the twofold inversion axis is the same as a mirror plane perpendicular to that axis.;把一个结晶多面体所具有的全部宏观对称要素以一定的顺序组合起来，就构成了该结晶多面体的对称型。 排列顺序为：对称轴Ln（由高到低）、对称面P、对称心C.;;1-3. Symmetry and Choice of Unit Cell; ;2) Abstraction of Parallelepiped / Prism;Principle of Abstracting Parallelepiped ;Example: C