7/24/2019 Imperfections in Solids.pptx
1/36
Imperfections in
Solids
7/24/2019 Imperfections in Solids.pptx
2/36
Why Study Imperfections inSolids? The properties of some materials are profoundly inuenced b
the presence of imperfections. Consequently, it is important t
have a knoled!e about the types of imperfections that e"ist anthe roles they play in a#ectin! the behavior of materials. $o
e"ample, the mechanical properties of pure metals e"periencsi!ni%cant alterations hen alloyed &i.e., hen impurity atom
are added'(for e"ample, brass &)*+ copper-*+ inc' is mucharder and stron!er than pure copper &Section )./'. 0ls
inte!rated circuit microelectronic devices found in ou
computers, calculators, and home appliances function because hi!hly controlled concentrations of speci%c impurities that ar
incorporated into small, localied re!ions of semiconductinmaterials
7/24/2019 Imperfections in Solids.pptx
3/36
three basic types ofimperfections1 point defects,
line defects (or dislocations), and
surface defects.
7/24/2019 Imperfections in Solids.pptx
4/36
23I4T 56$6CTS
2oint defects are localied disruptions in otherisperfect atomic or ionic arran!ements in a crystastructure
These imperfections may be introduced by movemenof the atoms or ions hen they !ain ener!y by heatin!
durin! processin! of the material, or by the intentionaor unintentional introduction of impurities.
7/24/2019 Imperfections in Solids.pptx
5/36
IMPURITIESare elements or compounds that are present from ramaterials or processin!. $or e"ample, silicon crystals !ron inquart crucibles contain o"y!en as an impurity.
DOPANTS, on the other hand, are elements or compounds that aredeliberately added, in knon concentrations, at speci%c locations i
the microstructure, ith an intended bene%cial e#ect on propertiesor processin!
7/24/2019 Imperfections in Solids.pptx
6/36
T726S 3$ 23I4T 56$6CTS
8. 90C04CI6S
:. I4T6;STITI0< 0T3=
-. S=0STIT>TI340< 0T3=
@. STIT>TI340< 0T3=
B. $;646< 56$6CT
D. SCE3TT7 56$6CT
7/24/2019 Imperfections in Solids.pptx
7/36
90C04CI6S
0 vacancy is produced hen an atom or an ion is missin! from itsnormal site in the crystal structure
7/24/2019 Imperfections in Solids.pptx
8/36
The equilibrium number of vacancies for a !iven quantity ofmaterial depends on and increases ith temperature accordin! to
7/24/2019 Imperfections in Solids.pptx
9/36
6F0=2
7/24/2019 Imperfections in Solids.pptx
10/36
6F0=2
7/24/2019 Imperfections in Solids.pptx
11/36
I4T6;STITI0< 56$6CT
0n interstitial defect is formed hen an e"tra atom orion is inserted into the crystal structure at a normallyunoccupied position
7/24/2019 Imperfections in Solids.pptx
12/36
Interstitial atoms or ions, althou!h much smaller than the atoms oions located at the lattice points, are still lar!er than the interstitialsites that they occupyM consequently, the surroundin! crystal re!iois compressed and distorted.
Interstitial atoms such as hydro!en are often present as impuritieshereas carbon atoms are intentionally added to iron to produce
steel. $or small concentrations, carbon atoms occupy interstitialsites in the iron crystal structure, introducin! a stress in thelocalied re!ion of the crystal in their vicinity
7/24/2019 Imperfections in Solids.pptx
13/36
6F0=2
7/24/2019 Imperfections in Solids.pptx
14/36
7/24/2019 Imperfections in Solids.pptx
15/36
S>STIT>TI340< 56$6CT
0 substitutional defectis introduced hen one atom oion is replaced by a di#erent type of atom or ion. Thsubstitutional atoms or ions occupy the normal latticsite. Substitutional atoms or ions may either be lar!ethan the normal atoms or ions in the crystal structure, ihich case the surroundin! interatomic spacin!s arreduced, or smaller causin! the surroundin! atoms thave lar!er interatomic spacin!s.
7/24/2019 Imperfections in Solids.pptx
16/36
7/24/2019 Imperfections in Solids.pptx
17/36
3TE6; 23I4T 56$6CTS
0n interstitialcis created hen an atom identical to those at thenormal lattice points is located in an interstitial position. Thesedefects are most likely to be found in crystal structures havin! a lopackin! factor.
0 !ren"el defectis a vacancyJinterstitial pair formed hen anion Numps from a normal lattice point to an interstitial site, leavin!behind a vacancy. 0lthou!h, this is usually associated ith ionicmaterials, a $renkel defect can occur in metals and covalentlybonded materials
7/24/2019 Imperfections in Solids.pptx
18/36
7/24/2019 Imperfections in Solids.pptx
19/36
0 Sc#ott" defectis unique to ionic materials and is commonlyfound in many ceramic materials. When vacancies occur in anionically bonded material, a stoichiometric number of anions andcations must be missin! from re!ular atomic positions if electricalneutrality is to be preserved. $or e"ample, one =!O: vacancy andone 3J: vacancy in =!3 constitute a Schottky pair. In Pr3:, for onePrO@ vacancy, there ill be to 3J: vacancies.
7/24/2019 Imperfections in Solids.pptx
20/36
7/24/2019 Imperfections in Solids.pptx
21/36
5IS
7/24/2019 Imperfections in Solids.pptx
22/36
SC;6W 5IS
7/24/2019 Imperfections in Solids.pptx
23/36
7/24/2019 Imperfections in Solids.pptx
24/36
7/24/2019 Imperfections in Solids.pptx
25/36
7/24/2019 Imperfections in Solids.pptx
26/36
65A6 5IS
7/24/2019 Imperfections in Solids.pptx
27/36
7/24/2019 Imperfections in Solids.pptx
28/36
7/24/2019 Imperfections in Solids.pptx
29/36
7/24/2019 Imperfections in Solids.pptx
30/36
=IF65 5IS
7/24/2019 Imperfections in Solids.pptx
31/36
>;A6;S 96CT3;
JJJJ The displacement vector that Qcloses the loopR hen traversin!an equal number of lattice steps around the defect
JJJJ denoted by QbR
JJJJJ it is parallel in the line of dislocation in scre dislocation and isperpendicular in the line of dislocation in ed!e dislocation
7/24/2019 Imperfections in Solids.pptx
32/36
ur!ers vector in scredislocation
7/24/2019 Imperfections in Solids.pptx
33/36
ur!ers vector in ed!e dislocation
7/24/2019 Imperfections in Solids.pptx
34/36
6"ample1
Calculate the len!th of bur!er vector in copper &$CC crystalstructure'
7/24/2019 Imperfections in Solids.pptx
35/36
7/24/2019 Imperfections in Solids.pptx
36/36
S>;$0C6 56$6CTS