材料科学专业英语课件1.ppt

1、Correction“Principle quantum number”should be corrected as“Principal quantum number”.-1-Atomic Structure Atomic structures electronNucleus-Atom consists of nucleus(positive charged)and Electrons(negative charged)H(1):1s1C(6):1s22s22p2O(8):1s22s22p4Si(14):1s22s22p63s23p2 Only those electrons which oc

2、cupy the outermost shell will involve in chemical reaction;called valence electrons The outer shell need to be fully filled for being stable Pauli exclusion principle:only two electrons can occupy the same orbital-2-Atomic bonds-Metallic bondingThe valence electrons are freely shared by all the atom

3、s in the structure.-Ionic bondingAtom give up one or more electrons positive charge(Cation)Atom accept one or more electrons negative charge(Anion)Coulombic attraction force source of ionic bonding-Covalent bondingTwo or more atoms share electrons such that each achieves stability.covalent bonding i

4、s directional-3-Chapter 2:Crystal Structures Crystalline structure:regular,long range order Amorphous(glass)structure:no long range order-4-Close-Packed Structures Crystalline structure-5-Close-PackedNon-Close-Packed-Close-Packed Structures Position aPosition b Crystalline structureLayer ALayer B-6-

5、Close-packed cubic structure-FCC ABCABCFirst Layer ASecond Layer BThird Layer C-7-Close-packed hexagonal structure-HCPFirst Layer ASecond Layer BThird Layer AABAB-8-In cubic structure,if atom C is shifted to the position circled by the dash line,fcc stacking may be converted to the hcp stacking.-9-L

6、attice Parameters of the unit cell:axial lengths(a,b,and c)angles between axes(,and )-10-Lattice:means a three-dimensional array of points coinciding with atom positions(or sphere centers).-Unit cell:the smallest group of atoms that shows the geometry of the structure.-7 possible unit cell geometrie

7、sdistinguish from each other by length of unit cell edges and the angles between the edges-11-12-PositionThe position of an atom is described with reference to the axes of the unit cell and the unit dimensions of the cell E.g.FCC structureabcdea:0,0,0b:0,0,1c:0,1,1d:1,1,1e:21,0,21ff:21,1,21-13-Cryst

8、allographic Directions and Planes(Miller indices)xyz110111112Define direction and planes in unit cellDirection,hkl Draw a vector from original point along the direction to be defined Project it on three axes multiple three number to get minimum integers Equivalent direction-14-xyzPlanes:(hkl)(111)(1

9、10)(010)Find intercepts with x,y,z Get reciprocals Multiple the reciprocals to get minimum integers Equivalent plane -15-HCP structure Miller indices-Direction uvtwt=-(u+v)-16-Conversion from 3-index system to 4-index system010 in 3-index system becomes 1120 in 4-index system.-17-HCP structure Mille

10、r indices-Planes(hkil)Basal plane:(0001)Prism plane:(1010)(0110);(1100)i=-(h+k)-18-Determination of Miller Indices for a Plane Within a Hexagonal Unit CellTherefore the(hkil)indices are(1101).-19-Linear density(LD)and close packed directionExample 1:FCC structure110 direction:aaa22222/112/1If the ra

11、dius of atom is r:ra22100 direction:aa12/12/1110 is close packed direction(001)plane-20-Example 2:BCC structure111 direction:aa3232/112/1If the radius of atom is r:ra34100 direction:aa12/12/1111 is close packed direction(110)plane110 direction:aa2122/12/1-21-Example 3:simple cubic structurera2100 is

12、 close packed direction(100)plane110 direction:aa2122/12/1100 direction:aa12/12/1-22-Example 4:HCP structurera2(0001)Basal planea1,a2,a3 are close packed directionsa1,a2,a3 directions:aa12/12/1a1a2a3c(2110)c=1.633 a0001 directionac633.112/12/1-23-Planar density and close packed planeExample 1:FCC st

13、ructure22a(111)is close packed plane(001)plane(111)plane(011)plane22222212414aa223423213613aa-24-Example 2:BCC structure(110)plane222a(100)plane21a(110)Has higher planar density than(100)Example 3:HCP structure(0001)Basal plane(0001)is close packed planea1a2a3c223423213613aa(1010)Prism plane 2633.11

14、1aac-Packing densityVolume occupied by atoms/unit cell volume-FCC/HCP structure(they are the same)74.0)22(3443443333rrar-BCC structure68.0)34(3423423333rrar-Simple cubic structure52.0)2(34343333rrar-Plane spacing:-Different crystal has different equation-Cubic:222221alkhd222222341clakhkhd-Hexagonal:d=a:2/ad 3/ad The distance between two parallel planesExercise determine the miller indices of the plane shown in the hexagonal unit cellAssuming a=c,calculate the distance between two parallel plansBraggs equation