材料科学基础英文版课件1

Chapter 1 Fundamental Concepts of Crystal11) Definition of Crystal1-1. Basic Concepts of Crystal What is Crystal？ Crystal and Amorphous2 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.Quartz3 Later, all solids with geometrical polyhedron shape were defined crystal, such as salt, calcite, magnetite.Salt CalcitemagnetiteRuby / CorundumDiamondZircon4SaltQuartzBerylRed Beryl5The building blocks of these two are identical, but different crystal faces are developedCrystal StructureCleaving a crystal of rocksalt6 The external appearance of crystals are all characterized by flat bounding planes which intersect at characteristic angles. Why many rounded stones and man-made cast solid objects with no external evidence are observed?Question:78 Definition of crystalCrystals are built up of regular arrangements of atoms, molecules or ions in three dimensions.晶体是内部质点在三维空间呈周期性重复排列的固体；或者说，晶体是具有格子构造的固体。82) Space Lattice and Equivalent PointsEquivalent Point: Identical Surroundingsthe grouping of lattice points about any given point is identical to the grouping about any other point in the lattice. 9Equivalent Points, Space Latticeperiodic array of points in three dimension Space LatticeLattice PointsEquivalent Point: Identical position and identical surroundingi.e. Cl- center、 Na+ center、 between Cl- thus, individual pentagons have fivefold symmetry but the array of pentagons does not.deadspaceThe impossibility of forming a complete layer of pentagonsA complete layer of hexagons28Symmetry Elements of CubeSymmetry Elements: (A) center of symmetry; (B) mirror plane; (C) twofold rotation axis; (D) fourfold rotation axis29Inversion Axis Inversion Axis (Lin / n) inversionA combined symmetry operation involving rotation (according to n) and inversion through the center. Possible inversion