Imperfection of Solid & Atom Movements

8/11/2019 Imperfection of Solid & Atom Movements

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Imperfection of Solid & Atom movements

Subject: Elektrokimia Fasa Padatan

Dr. Fitria Rahmawati


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IMPERFECTION IN SOLID

Ideal solid does not exist, all contain defects

or imperfection.

Many defects available:1. Point defect

2. Linear defect3. Interfacial defect (boundaries)


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1. Point Defect:There are two types of point defect based on its

process of defect formation:1. intrinsic defect

the increase of entropy of crystal

2. extrinsic defect

defect which may occur in isolation in order

to balance the presence of impurity


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Intrinsic Point Defect Schottky Defect

Schottky defect consist of charge balancingcation and anion vacancies.


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Frenkel Defect

a defect due to atoms at interstitial position or a

place outside normal position.

Cation is displaced from normal to interstitial lattice


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Frenkel cation defect is more common due to

smaller size of cation hence easier to beoccomodated in interstitial site


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Color Centres Electrons are trapped in vacant sites give rise to

color materials

Trapped electrons can be made by:

1. irradiation of the sample

Irradiation can lead defect where an electron has beenadded or losed

2. treatment with an electron donor like sodium or

potassium donor Treatment with alkali metal vapour could produce electron

excess in material


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F, H and V Color Centres


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Application of color centre of BaFBr:Eu2+ phosphors in medical X-ray

analysis


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Extrinsic point defect Extrinsic defect will be produced when a cationic impurities or

dopants are introduced into solid however the dopant does not

have the same valence as cation which has been replaced. Examples:

Fe1-x O : cation vacancies

Ca2+ in ZrO2 : anion vacanciesY3+ in ZrO2 : anion vacancies

Ca2+ or Cd2+ in NaCl : cation vacancies


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Crystal structure of Fe1-xO


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Real crystals may contain both intrinsic and

extrinsic defect. The dominant defect depends

upon temperature and doping level


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2. Linear defect (Line defect)Line defect or dislocation mainly caused by the absence of ions in

a line structure or named as mis-alignment, or because of the

existence of vacancies along the line, these defect is called asedge dislocation. When the mis-alignment lead to the

movement of a block of ions gradually upward or downward, it

as screw dislocation (Rahmawati, 2012)

This defect can occur due to:

-mechanical stress and deformation

- unperfected crystal growing


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Most dislocation have mixes edge and screwcharacter


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3. Interfacial DefectInterfacial Defect is boundaries that have two dimensions and

normally separate regions of the materials that have different

crystal structures and / or different crystallographic orientation


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ATOM MOVEMENTS

(Rahmawati, 2012)


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(Rahmawati, 2012)


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References: Callister, W. (2000) Material Science and Engineering: An

Introduction, 5th edition, John Wiley & Sons, Inc., New Jersey.

De Guire, M.R. (2003) Introduction to Materials Science &Engineering, EMSE 201.

Effendy (2008) IKATAN IONIK dan cacat-cacat pada kristal ionik,

edisi 2, bayumedia Publishing, Malang. Rahmawati, F. (2012) Zirconia-LSGM Based Materials as

Electrolyte for SOFC, the mixtured materials for solid electrolyte,

LAP LAMBERT academic Publishing, Saarbrken, Germany. West, A. (1999) Basic Solid State Chemistry, second edition,

John Wiley & Sons, Ltd., Chichester, Ohio.

Imperfection of Solid & Atom Movements

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