Introduction Part 3-Solid State Physics-Lecture Slides, Slides of Solid State Physics

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Crystal Structure 101

Example; Atomic Packing Factor

Crystal Structure 102

2 - HEXAGONAL SYSTEM

 A crystal system in which three equal coplanar axes

intersect at an angle of 60 , and a perpendicular to the

others, is of a different length.

Crystal Structure 105

3 - TRICLINIC

4 - MONOCLINIC CRYSTAL SYSTEM

 Triclinic minerals are the least symmetrical. Their three axes

are all different lengths and none of them are perpendicular

to each other. These minerals are the most difficult to

recognize.

Triclinic (Simple)  ß  90 oa  b  c

Monoclinic (Simple)  =  = 90o, ß  90 o a  b  c

Monoclinic (Base Centered)  =  = 90o, ß  90 o a  b  c,

Crystal Structure 107

6 – TETRAGONAL SYSTEM

Tetragonal (P)

 = ß =  = 90o

a = b c

Tetragonal (BC)

 = ß =  = 90o

a = b c

Crystal Structure 108

7 - Rhombohedral (R) or Trigonal

Rhombohedral (R) or Trigonal (S)

a = b = c,  = ß =  90 o

Crystal Structure 110

1 – Sodium Chloride Structure

 Sodium chloride also crystallizes in a cubic lattice, but with a different unit cell.

 Sodium chloride structure consists of equal numbers of sodium and chlorine ions placed at alternate points of a simple cubic lattice.

 Each ion has six of the other kind of ions as its nearest neighbours.

Sodium Chloride Structure

 This structure can be

considered as a face-

centered-cubic Bravais lattice

with a basis consisting of a

sodium ion at 0 and a chlorine

ion at the center of the

conventional cell,

 LiF,NaBr,KCl,LiI,etc

 The lattice constants are in

the order of 4-7 angstroms.

/ 2 ( )

   a x  y  z

Crystal Structure 114

2-Cesium Chloride Structure

Cs+Cl-

 Cesium chloride crystallizes in a

cubic lattice. The unit cell may be

depicted as shown. (Cs+ is teal,

Cl- is gold).

 Cesium chloride consists of equal

numbers of cesium and chlorine

ions, placed at the points of a

body-centered cubic lattice so that

each ion has eight of the other kind

as its nearest neighbors.

8 cell

Cesium Chloride Cs+Cl-

Crystal Structure 117

3 – Hexagonal Close-Packed Str.

 This is another structure that is common, particularly in metals. In addition to the two layers of atoms which form the base and the upper face of the hexagon, there is also an intervening layer of atoms arranged such that each of these atoms rest over a depression between three atoms in the base.

Crystal Structure 119

A A

A A

A A

A

A A A

A A

A A^ A

A A^ A

B B

B

B

B B

B

B

B

B B

C C C

C^ C

C

C

C C C

Sequence ABABAB.. -hexagonal close pack

Sequence ABCABCAB..

• face centered cubic close pack

Close pack

B

A A

A A

A

A

A

A A

B

B (^) B

Sequence AAAA…

• simple cubic

Sequence ABAB…

• body centered cubic

Packing

• Crystal Structure
• Crystal Structure