Post on 10-Oct-2015
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METALURGI FISIK
Cacat Kristal
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Cacat Kristal
1. Ketidaksempurnaan kristal
2. Sejumlah cacat kecil dapat menyebabkan kristallogam 1000 x lebih ulet dari yang tanpa cacat
3. Terbentuk pola yang tidak berulang pada struktur
kristal4. Jenis cacat berdasarkan ukuran cacat :
* cacat titik/ point defects (0-Dimension)
* cacat garis / Line defects (1-D)
* cacat bidang / Interfacial defects (2-D)
* cacat ruang / Bulk defects (3-D)
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0D
(Point defects)
Vacancy
Impurity
Frenkel defect
Schottky defect
Non-ionic
crystals
Ionic
crystals
Imperfect point-like regions in the crystal about the size of 1-2 atomic
diameters
Interstitial
Substitutional
Other ~
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Cacat Titik :
Cacat yang disebabkan oleh adanyakekosongan/lolosnya atom dari susunannya
Penyebabnya :
1. Tumpukan atom tidak sempurna selama proses
kristalisasi
2. Akibat vibrasi atom pada saat penurunan suhu
Cacat titik dapat berupa:
Vacancy, Divacansy, dan Trivacancy
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Vacancy
Missing atom from an atomic site
Atoms around the vacancy displaced
Tensile stress field produced in the vicinity
Tensile Stress
Fields ?
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Vacancies:-vacant atomic sites in a structure.
Self-Interstitials:-"extra" atoms positioned between atomic sites.
Point Defects
Vacancy
distortion
of planes
self-interstitial
distortionof planes
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Impurity
Interstitial
Substitutional
SUBSTITUTIONAL IMPURITY Foreign atom replacing the parent atom in the crystal
E.g. Cu sitting in the lattice site of FCC-Ni
INTERSTITIAL IMPURITY
Foreign atom sitting in the void of a crystal
E.g.C
sitting in the octahedral void in HT FCC-Fe
Compressive stress
fields
Tensile StressFields
Compressive
Stress
Fields
Relative
size
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Larutan padat interstisiLarutan padat subsitusi
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Extrinsic defects (due to impurities)
Impurities or dopants in a solid are any atom(s) of a type that do not belong in theperfect crystal structure (see extrinsic semiconductors)
The host crystal with impurities is called a solid solution
Substitutional solid solutions
Impurit y atoms occupy the same sites of
the host atoms
Impurities "substitute" for the host atoms
Interstitial solid solutions
Impurit y atoms occupy interstices in the
host crystal structure
Impurities usually have a small size
compared to the host atoms
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Ionic Crystals
Overall electrical neutrality has to be maintained
Frenkel defect
Cation (being smaller get displaced to interstitial voids
E.g. AgI, CaF2
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Schottky defect
Pair of anion and cation vacancies E.g. Alkali halides
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Frenkeldefect
Schottkydefect
Defects in ionic solidsDefects in ionic solids
Cation vacancy+
cation interstitial
Cation vacancy+
anion vacancy