mse 131 ceramics lecture 1 2016 student

7/26/2019 MSE 131 Ceramics Lecture 1 2016 Student

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MSE 131 CeramicsLecture 1

Dr. Benjamin O. Chan

Physics Department

Ateneo de Manila University2016


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Types of Ceramics

Traditional ceramicsAbrasive products, clay products, construction,

glass, refractories, whitewares Industrial/Engineering/Advanced ceramics

Automotive, aerospace, electronics, hightemperature, manufacturing, medical

Fine ceramics Very small grain sizes

Nanoceramics


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Ceramic Bonds

Covalent

Electrons shared betweenatoms

Ionic One atom gives willingly, the other readily takes

Extreme form of covalent bond


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Partially Covalent/Ionic Bonds


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Associated Crystal Structures

Diatomic Structures

Diamond/Zincblende

CsCl

NaCl


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Stability of Anion-Cation

Configurations


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Stable Configurations I


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Determining Critical Size


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Stable Configurations II


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Some Ionic Radii


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Stable Crystal Structures

Things to consider

Difference in electronegativity

Atomic bonding Stoichiometry

r/R ratio

Coordination number


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Example: MgO

EN = 3.44-1.31 = 2.13 (68% ionic)

Ionic Bond between Mg and O

r(Mg2+

) = r = 0.078 nm r(O2-) = R = 0.132 nm

r/R = 0.078/0.132 = 0.591

CN = 6

NaCl structure Diatomic FCC with

octahedral sites filled bycations


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Example: CsI

EN = 2.66 0.79 = 1.87

58% ionic

r/R = 0.167/0.220 = 0.76,CN = 8

CsCl structure

Diatomic simple cubicstructure with the bodycenter occupied by acation


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Example: GaAs

EN = 2.18 1.81 = 0.37, 3% ionic

metallic or covalent

Valence = (3+5)/2 = 4 > 3Covalent bond

CN = 8 Valence = 4

Zincblende structure

Diatomic FCC with thecation occupying


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What happens if the cationand anion are of the same

size?


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Atomic Packing Factor: NaCl

Fractional volume occupied by atoms

r(Na+) = r = 0.098 nm

r(Cl

-

) = R = 0.181 nm

APF = 66.3%

3

33

3

33

)(3

2

8

)3

43

4(4

Rr

Rr

Rr

Rr

APF


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Density Calculation: CsCl

r(Cs+) = 0.167 nm

r(Cl-) = 0.181 nm

AtWt(Cs+) = 132.9 g/mol

At Wt(Cl-) = 35.45 g/mol M = (132.9g/6.023x1023) + (35.45/ 6.023x1023)

= 2.8 x 10-22g

V = ao3 = (2(0.167nm+0.181nm)/31/2)3

= 6.49x 10-23

cm3

= M/V = 2.8x10-22g/ 6.49x 10-23cm3

= 4.31 g/cm3

*experimental density is 3.99 g/cm3


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Three or more atoms in the basis

Fluorite (CaF2)

Perovskite (BaTiO3)

Crystobalite (SiO2)


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Silicates

Main components are Si and O

Consider arrangement of SiO44-

tetrahedron


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Silica

Every corner O in each tetrahedron is shared

by adjacent tetrahedra

Polymorphic forms: quartz, crystobalite,tridymite


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Silicates

Corner atom shared by 1, 2 or 3 tetrahedra

Cations (Ca2+, Mg2+,Al3+) compensate

negative tetrahedral charge and bond themtogether

a) Forsterite (Mg2SiO4)

b) Akermanite

(Ca2MgSi2O7)


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Layered Silicates

Sheet forms on sharing 3 O ions (Si2O5)2-

Second sheet neutralizes sheet

Kaolinite clayAl2(Si2O5) (OH)4

Talc

Mg3(Si2O5) 2(OH)2

Mica

KAl3Si3O10(OH)2


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Carbon

Diamond

Graphite

Fullerenes

CNT


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Homework

Compare the densities of diamond,

graphite, fullerene and carbon

nanotubes. Make observations orcomments on the values.


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Piezo-ceramics

Induced polarization upon

application of stress

Inverse effect: application of

electric field generates stress

Curie temperature

Transformation from cubic to

orthorhombic Orthorhombic structure is

susceptible to polarization


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Piezo-ceramics

Poling generates hysteresis

and remanent polarization


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Piezo-ceramics

Hard

Can be exposed to repetitive high electrical

and mechanical stresses Ideal for high-power and ignition applications

Soft

Relatively easy polarization

Suitable for sensing applications, receivers,

actuators and low power transducers


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More Complex Structures

More than one

compound

YBCOsuperconductor


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Non-crystalline Structures

GlassAmorphous structure

Fused/vitreous silica Network formers

B2O3 and GeO2

Network modifiers Na2O, CaO

Intermediates

TiO2, Al2O3


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Determining Crystal Structure

Indirect method

Diffraction (probe beam must have

wavelength < lattice spacing)Direct method

STM

AFMCan only see surface and immediate layers

below it


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Determining Composition

Spectroscopy

UV-VIS

IR X-ray

Mass spectroscopy

Nuclear Magnetic Resonance

Rutherford Backscattering

Neutron Activation Analysis


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Crystal Defects

Point: 0-D

Line: 1-D

Area: 2-D

Volume: 3-D


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Point Defects

Vacancies

Missing host atom

Self-interstitialsDisplaced (misplaced)

host atom

Impurities

Foreign atoms Interstitial

Substitutional


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Ionic Crystal Point Defects

Charge neutrality maintained

Frenkel Defect: vacancy-interstitial pair

Schottky Defect: vacancy pair


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Impurities

Intrinsic Starting material (from growth)

Extrinsic From material processing

From device fabrication

Intentional

To attain desired property Included during growth or processing

Doping

Charge neutrality is maintained


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Location of Impurities Interstitial

Occupying interstitial sites (in between host atoms)

Substitutional Occupying vacancy sites (replacing host atoms in the lattice)


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Interstitial or Substitutional?

Hume-Rothery rules Size difference not greater than 15%

EN comparable

Similar valence ( 1, 2)* same crystal structure

for complete solubility

can be ignored for dilute solutions

Satisfy first three conditions, impurity atomwill occupy a substitutional site

Otherwise, interstitial site Size must be comparable to interstitial site

mse 131 ceramics lecture 1 2016 student

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