electrical properties of polymers, ceramics, dielectrics, and amorphous...

Electrical Properties of Polymers, Ceramics, Dielectrics, and

Amorphous Materials

Dae Yong JEONG

Inha University

Review & Introduction

We learned about the electronic transfer in Metal and

Semiconductor.

In general, Polymer and ceramic materials are

insulating. But, some polymers and ceramics show

S.C and conducting properties.

Beside electron, Any other charges?

Ionic conduction

For insulating materials, what happens under E-field?

Capacitor (condenser)

* Same Materials for different naming • For used for insulation (Generally for DC) Insulator

• For used for AC current For materials, Dielectrics

• For circuit, Capacitor (condenser) : Dielectric materials for capacitor application

Materials vs Conductivity

Conductor Semiconductor

Insulator (utilize R ~ ∞)

Dielectric for AC

Capacitor (C) in circuit

Metal Most Si ?

Ceramic

Electron conductor

ITO

IrO2, RuO2,

SrRuO3 ZnO, SnO2, TiO2

etc (some) Most

Ionic conductor

ZrO2 (O2-),

Na3Zr2Si2PO12

(NASICON: Na+)

Polymer Conducting

polymer (rare)

Conducting

polymer (rare) Most

Charge Transport in Materials

Electronic Conductor Ionic Conductor

Materials

Metal

Semiconductor

Al, Cu

Si, GaAs

SnO2, ZnO, TiO2

LiMnO2

Semiconducting polymer

Electrolyte (solid, liquid)

ZrO2

Li-polymer electrolyte

Applications

Electric connection (metal)

Semiconductor device

Opto-electronic device

(LED, LASER, Solar Cell)

Battery electrode

Fuel cell

Battery

Electrochemical sensor

O2- transport

Light metal ion (Li+, Na+ …)

9.1. Conducting Polymers and Organic Metals

About “Polymer”

Basically Carbon (C: 1S2 2S2 2P2) based materials

Depending on bond, different hybridization

The simple repeating unit of a polymer is the monomer.

Copolymer is a polymer made up of two or more monomers

Styrene-butadiene rubber

(CH CH2 CH2 CH CH CH2)n

Homopolymer is a polymer made up of only one type of monomer

( CF2 CF2 )n

Teflon

( CH2 CH2)n

Polyethylene

(CH2 CH)n

Cl

PVC

• % Crystallinity: % of material that is crystalline. -- Tensile stress and Young’s modulus often increase with % crystallinity.

-- Annealing causes crystalline regions to grow. % crystallinity increases.

crystalline region

amorphous region

Microstructure & Crystallinity

Molecular Orbital Theory

Similar to Band Theory

Powerful to explain the electronic properties in polymer Different material different suitable theory

Energy level can be calculated as,

A bonding molecular orbital has lower energy and greater

stability than the atomic orbitals from which it was formed.

An antibonding (*) molecular orbital has higher energy and

lower stability than the atomic orbitals from which it was formed.

9.1. (S.C) Conducting Polymers and Organic Metals

Conduction polymer

Peculiar property in polymer

OLED, capacitor, sensor, photovoltic devices, antistatic…

crystalline region

amorphous region

Distinct band structure

(From Molecular orbital theory)

Periodic structure

(High conductivity)

9.1. (S.C) Conducting Polymers and Organic Metals

For example,

Polyacetylene Conjugated organic polymer: alternating single and double bond

High conductivity from a high degree of crystallinity.

Conductivity ~ comparable to Si

From Electronic properties of materials, Fourth Edition, Hummel (© Springer, 2010)

Trans Polyacetylene

Cis Polyacetylene

Different structure

Different conductivity


Calculation (a)/observation of Band Structure

Trans Polyacetylene

Same length

Continuous band

Metallic

In reality, no same length

Little difference/ large difference

Band gap

S.C/insulating


Where are electrons in conduction band from?

Double bond weak bond, easy breakage easily disassociated by thermal energy easily accelerated by E-field

Electron properties The effective mass: m* = 0.6 mo at k = 0, 0.1 mo at k = π/a

For τ 10-14s μ ~ 200 cm2/Vs

LUMO

Lowest Unoccupied Molecular Orbital

(similar to conduction band)

HOMO

Highest Occupied Molecular Orbital

(similar to valence band)

Band width: 10- 14 eV

Band gap: 1.5 eV

How to increase the conductivity?

Same length bw carbon (Fig. 9.5 (a))

Doping (20 ~ 40%, lot of amount!!)

Arsenic-pentafluoride ~ x 107

undoped trans- comparable to that

of metal

Oxidant p-type

Alkali metal n-type


How to explain the conduction in polymer?

In fact, the conduction in polymer is different from metal and S.C such as Si.

In metal and S.C, conduction was explained with electron movement. Where, electrons are from ionization.

But, polymer conduction is from breakage of pi-bonding.

Let’s introduce “SOLITONs” for the conduction in polymer.

Double-single-double-single- Double-single-single- double-single-

Locally negative (soliton)

Seem like “additional energy level in forbidden band.”

Same length at the center of a soliton

Many soliton over lap metallic

Soliton movement (soliton wave) ~ moving electron


9.1. Conducting Polymers and Organic Metals

Conducting polymer Polyanilines

Polypyrroles

Polythiophenes

Polyphenylenes

Poly(p-phenylene vinylene)

……

PEDOT : poly(3,4-ethylenedioxythiophene) water soluble

With thin layer transparent

OLED, sensor, flexible device, wearable device..…

Toxic, poor stability, sensitive to environmental condition

9.2. Ionic conduction

In general, ionic X-tal large band gap insulating

Ion movement (hop from lattice site to lattice site under E-field)

ionionion eN

Question

Which conditions are required for ion to move?

Sufficient energy to overcome energy barrier

Empty site (vacancy) around movable ions (defects)


Defect in Ceramic (charge carrier)

Δ E

Δ T

Δ C

conduction

Electrical

chemical

Why defects inside crystal?

Thermodynamical explanation

Naturally with Defect increase randomness (mixture)

lower E

STHG

Defect in Ceramic (charge carrier)

What kind of defects (intrinsic)?

Mi

X

M VMM

Metal move to another interstitial place

Metal gone vacancy generation, effective charge (-2)

At the same time

Insertion of Metal ion effective change (+2)

MO VVnull

(Metal ion & Oxygen ion) gone

Oxygen ion gone vacancy generation, effective charge (+2)

At the same time

Metal ion gone vacancy generation effective change (-2)

Frenkel defect

Schottky defect


Nion : ~ # of defect

μion ~ ΔC (concentration of defects) Diffusion

ionionion eN

Diffusion: movement due to the gradient of concentration

Fick’s first law for Diffusion

Tk

De

B

ion

mxm

mols

Dsm

mol

dx

dDJ

distance:,ion concentrat :,mtcoefficiendiffusion : ,flux] [diffusion: J

3

2

3

Mobility is related with diffusion coefficient. [Einstein Relation]

Larger Diffusion coefficient fast movement

High Temp scattering increases

larger diffusion coefficient (D is function of T.)


Energy. activation is Q ,exp

Tk

QDD

B

o

Temp effect on Diffusion coefficient:

Arrhenius Eq.

Tk

Q

Tk

Q

Tk

DeN

Tk

Q

Tk

Q

Tk

DeN

B

oion

BB

oiono

B

o

BB

oionion

1lnln

exp

expexp

2

2

ionionion eN Conductivity of ionic materials



From experimental

data (beside) slope

activation energy

extrinsic region

Temp increase easy movement

High temp: intrinsic region

Generate additional defects



Extrinsic Disorder : generated by the addition of

impurities or solutes

Example: CaO doped ZrO2-δ Nonstoichiometric

compound

OZr VaCCaO

As Ca2+ substitutes Zr4+, to maintain charge neutrality Oxygen

vacancy is formed resulting in the non-stoichiometric compound.

As there is Oxygen vacancies, O2- can move easily. (O2-

electrolyte for fuel cell.)

9.3. Electron conduction in Metal Oxides

Examples

ZnO Zn : 4S2 Zn2+ : 4S0

O : 2P4 O 2- (2 electrons from Zn): 2P6

ZnO: stoichiometric compound insulating or wide band gap S.C

ZnO1-δ (Oxygen vacancy) + 2e- n-type S.C

Sensor, varistor etc…

SnO2 In2O3 doped SnO2 ITO: transparent electrode with high conductivity

NiO Ni : 4S2 Ni2+ : 4S0

O : 2P4 O 2- (2 electrons from Zn): 2P6

Stoichiometric compound insulating

Nonstoichiometric : Ni1-δO (Ni vacancy) + 2P+ p-type S.C

9.4. Amorphous Materials (Metallic Glasses)

Most metal crystalline

Amorphous phase (metallic glasses or glassy metals) Rapid solidification ~ 105K/s

Short range ordering

Nondirectional bonding

Bloch theorem (periodic potential) for band calculation can not be utilized.

Nano-size grain: Unusual electrical, mechanical, optical, magnetic, corrosion properties.


9.4. Amorphous Materials (examples)

Amorphous metallic

Example: Cu-Zn

Partially filled band

But, small Z(E) at near EF

Poor conductivity (5 x 103 1/Ω cm)

Amorphous S.C Strong binding force localized energy

level, discrete energy level band gap

Small Z(E)

Small conductivity (10-7 1/Ω cm at RT)

H-doped a-Si for photovoltic device


9.4.1. Xerography (electrophotography) An important application of a-S.C (ex: a-Se, a-Si)

Laser printer or copy machine

a-S.C deposited

High voltage eletrostatic

charge on insulating a-S.C

Scanning light electron/hole pair generation

discharge the affected parts patterning

Charged toner with

magnetic particle

Transfer the charged

toner particles with

E-field

Adhere the polymer

toner particle onto

paper


Materials Scientists

PLS, be curious about the devices. How to operate?

What is the basic principle?

And, make your own ideas!! Environmentally friendly materials

Energy (materials) saving

Save the world and make money!!

Electronic Materials

Electron conductivity

Conduction (charge flow) V=iR (Ohm’s law) 전기장을 가하면, 전하가 이동 직선적으로 이동 Energy conversion: heat (i2R)

Conduction (charge flow) 전하의 농도를 조절 (Extrinsic S.C) “전하의 농도차에 의한 diffusion을 조절” Ex: P-N junction : Non-linear I-V behavior

Energy band…. Energy conversion (ex: light, E=hv)

Capacitive (charge storage) Energy conversion {ex:

Piezoelectric (size change)} …

electrical properties of polymers, ceramics, dielectrics, and amorphous...

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