ferroelectric and piezoelectric materials

7/21/2019 ferroelectric and piezoelectric materials

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Piezoelectric and Ferroelectric materials

Zaahir Salam



Some Basic Terms

• Dielectric Material- The Cumulative effect of microscopic displacements(charges,ions,electrons) results in Net Polarization due to setting up ofinduced dipole moments or due to rotation of permanent electric dipoleswhich are already present in the material.

• Dielectrics are the materials having electric dipole moment permantly.

• Polarization- Neutral Atom

In DC field +ve Nucleus is pushed in direction of Electric field.-ve Charged Electrons Pushed opposite to electric field.

Hence -ve and +ve Centres don’t coincide and undergo net displacement r .Dipole moment p= ( Ze)r.

p=αE

α - is known as polarizability of the atom(or molecule)

The induced charge on the surface of dielectric is polarization.

P= net dipole moment/ volume



• Polarization is due to shifting of

– Electron charge cloud (electronic polarization).

– Shifting of +ve and –ve ions (ionic polarization).

– Due to orientation of dipoles(orientation polarization).

• When there is shifting of ions or charge in there orientation of

dipoles there will be a slight change in the dimension of the

material- electrostriction effect (occurs in all dielectrics).



Cetro-Symmetric Piezoelectrics

(Non-Centro Symmetric)

Non-pyroelectrics Pyroelectrics

Non-Ferroelectrics Ferroelectrics

Dielectrics

Don’t Posses

Inversion centre

A Hierarchical Overlook



The History of Piezo

• The name Piezo originates

from the Greek word piezein, which means tosqueeze or press.

• The piezoelectric effect was

first proven in 1880 by thebrothers Pierre and Jacques

Curie.



What is Piezoelectric Material?

Piezoelectric Material is one that possesses the property of

converting mechanical energy into electrical energy and vice

versa.

Piezoelectric materials can be divided in 2 main groups:

crystals and cermaics.



Direct Piezoelectric Effect

• Piezoelectric Material will generate electricpotential when subjected to some kind of

mechanical stress.

•

The direct Effect : Strain Sensor, microphones,gas lighters, ultrasonic detectors

Compression

Effect: Decrease in volume and it has avoltage with the same polarity as the material

Tension

Effect: Increase in volume and it has a voltagewith opposite polarity as the material



Inverse Piezoelectric Effect

• If the piezoelectric material is exposed to an electric field

(voltage) it consequently lengthens or shortens proportional

to the voltage. E.g Crystal Oscillators, crystal Speakers,

record player Pic ups, actuators etc.

If the applied voltage has the same polarity

then the material expands.

If the applied voltage has the opposite

polarity then the material contracts.



The necessary condition for the piezoelectric effect is the absence of

a center of symmetry in the crystal structure. Of the 32 crystals

classes 21 lack a center of symmetry, and with the exceptions of one

class, all of these are piezoelectric.

If lead zirconate titanate (PZT), a piezoceramic, is placed between

two electrodes and a pressure causing a reduction of only 1/20 th of

one millimeter is applied, a 100,000-volt potential is produced.

The basic equations of piezoelectricity are:

P = D x stress and E = strain/D

Where,

P = Polarization,

E = electric field generated and

D = piezoelectric coefficient in metres per volt.



Naturally occurring crystals:Berlinite (AlPO4), cane sugar, Quartz, Rochelle salt,

Topaz, Tourmaline Group Minerals, and dry bone (apatite

crystals)

Man-made crystals:Gallium orthophosphate (GaPO4), Langasite

(La3Ga5SiO14)

Man-made ceramics:Barium titanate (BaTiO3), Lead titanate (PbTiO3), Lead

zirconate titanate (Pb[Zr x Ti1- x ]O3 0< x <1) - More commonlyknown as PZT , Potassium niobate (KNbO3), Lithium niobate(LiNbO3), Lithium tantalate (LiTaO3), Sodium tungstate

(NaxWO3), Ba2NaNb5O5, Pb2KNb5O15

Polymers:Polyvinylidene fluoride (PVDF)



Quartz(crystalline form of SiO2)

• Most abundant and widely used.

• Non- ferroelectric.

• Alternating field applied to the crystal-it vibrates

with a characteristic frequency which depends on

the crystal geometry.• Used as a dielectric-excellent frequency standard.

• Hexagonal structure.

• E.g crystal oscillators are used as frequencystandards in watches, electronic clocks, computer

clocks.



Polyvinylidene fluoride

•

In 1961 polyvinylidene fluoride, a piezoelectric plasticwas invented. It is one of the most widely usedpiezopolymer from which substantial electricity can begenerated. It is cheap and physically quite strong.

• In 2001 researchers found that PVDF becomessupersensitive to pressure when impregnated with verysmall quantity of nanotubes, thus PVDF with itsinherent superior mechanical properties when

upgraded with nano-technology produces a newgeneration of piezopolymer, which are durable and cangenerate large quantity of electricity economically.



• Although a number of polymers possess piezoelectric properties, none

match the magnitude of the effects in polyvinylidene fluoride (PVDF),

which is the most widely studied and commercially used piezoelectric

polymer. PVDF has been commercially available since 1965.

• Substantial piezoelectricity can be permanently induced by heating

stretched films of PVDF to about 1000C followed by cooling to ambient

temperature with a strong DC electric field (about 300kVcm-1) applied.

This treatment is called “Polling”.• Such polarization, attributed to redistribution of electronic or ionic

charges within the solids or injected from electrodes, characteristically

vanishes on exceeding some polarization temperature, Tp. The effect in

PVDF is totally different in that the induced polarization is thermally

reversible and polarizations current are, produced on either heating orcooling.

• When a sheet of PVDF is compressed or stretched, an electric charge is

generated and collected on the surfaces. The PVDF sheet is metallized on

both sides which acts as electrodes



PHYSICAL PROPERTIES OF PVDF Specific gravity: 1.75 -1.80;

melting point: 154-184

0

C; water absorption: 0.04-0.06%;

tensile strength at break: 36-56 Mpa;

elongation at break: 25-500%,

hardness shores D: 70-82;

low temperature embrittlement; -62 to 640 C.

Electrical Properties of PVDF(with out nanotubes impregnation)

Volume resistivity: 2x1014 ohm-cm;

Dielectric constant at 60 Hzs: 8.40 pm/V

Piezoelectric stress constant: 0.23V/ (m. pa)



Sonic and Ultrasonic Applications

• Sonar with Ultrasonic time-domain reflectometers.

• Materials testing to detectflaws inside cast metals

and stone objects.• Measure elasticity or

viscosity in gases andliquids

• Used in Compact sensitive

microphones and guitarpickups.

• Loudspeakers.



Pressure Applications

• Transient pressure measurement to

study explosives, internal combustionengines (knock sensors), and any othervibrations, accelerations, or impacts.

• Piezoelectric microbalances are used asvery sensitive chemical and biologicalsensors.

• Transducers are used in electronic drumpads to detect the impact of thedrummer's sticks.

• Energy Harvesting from impact on theground

• Atomic force and scanning tunnelingmicroscopes.

• Electric igniters and cigarette lighters



Consumer Electronics Applications

•

Quartz crystals resonators asfrequency stabilizers foroscillators in all computers.

• Phonograph pick-ups

• Accelerometers: In a

piezoelectric accelerometer amass is attached to a spring thatis attached to a piezoelectriccrystal. When subjected tovibration the mass compresses

and stretches the piezo electriccrystal. (iPhone)



Motor Applications

• Piezoelectric elements can be usedin laser mirror alignment, wheretheir ability to move a large mass(the mirror mount) over microscopicdistances is exploited. Byelectronically vibrating the mirror itgives the light reflected off it aDoppler shift to fine tune the laser'sfrequency.

• The piezo motor is viewed as a high-

precision replacement for thestepper motor.

• Traveling-wave motors used forauto-focus in cameras.



Ferroelectrics

All Ferroelectric materials exhibit Piezoelectric effect because –lack of symmetry.

Special Class of Piezoelectric Material- exhibit certain othercharacteristics also.

Exhibit spontaneous polarization i.e., polarization in theabsence of an electric field.

Ferroelectrics are the electric analog of the ferromagnets, whichmay display permanent magnetic behaviour.

Valasek discovered the first ferroelectric material, namelyRochelle salt.

In ferroelectrics, the polarization can be changed and evenreversed by an external electric field.



Ferroelectrics Continued

Properties

Spontaneous polarization in the absence applied

electrical field.

Extremely high dielectric constant (~500-15,000).

Strong non-linear dielectric response to an appliedelectrical field.

High strain response to applied electrical field

piezoelectricity

Strong variation in polarization with temperaturepyroelectricity



Polarisation vs. E-field

•

If we apply a small electric field, such that it is notable to switch domain alignments, then thematerial will behave as a normal dielectric:

P E

• As E is increased, we start to flip domains andrapidly increase P.

• When all domains are switched, we reachsaturation.

What happens if the E-field is now removed?



Spontaneous Polarization



• The value at zero field is termed the remnant polarisation.

• The value of P extrapolated back from thesaturation limit is the spontaneous polarisation.

• Reversal of the field will eventually remove allpolarisation – The field required is the coercive field .

• Further increasing the reverse field will completelyreverse the polarisation, and so a hysteresis loop isformed…



Perovskite Crystal Structure

General Formula: ABX3



Phase Transition

Charges CoincideCharges doesn’t Coincide

> 120°C< 120°C



Pyroelectric Materials

A special class of material which is subset ofpiezoelectric material.

Are polarized spontaneously but they do not respond

to an electric field like ferroelectronics –require very

high electric field for orienting the dipoles.

The field required is so high that the material reacheselectric breakdown before it can get polarized. But

When temperature is changed the polarization of

crystal changes. e.g LiNbO3

P l t i it



Pyroelectricity

0 100 200 300 400 5000.3

0.4

0.5

0.6

PbTiO3

T C =490oC

S p o n t a n e o u s P o l a r i z a t i o n

( C / m 2 )

Temperature [oC]

The spontaneous polarization is strongly dependent on the temperature. It dissapears

completely at the phase transformation temperature TC. The variation in the polarization

with respect to the temperature is called the pyroelectric effect.

T E

T

P

T

D p S

E



Applications of Ferroelectrics

Non-Volatile RAMs (memory)

Dynamic Capacitors.

Tunable Microwave Devices

Pyroelectric Detectors/Sensors

Optical Waveguides




The two possible orientations in these

materials make the materials attractive to

researchers developing computer memory

because one orientation could correspond to a

1 and the other to a 0. (Computer memory

stores information in 1’s and 0’s.)



Non volatile RAM continued…

•

These materials could help address the veryexpensive upkeep of cloud computing. Facebook,

Google, Web-based email and other services are

stored in the cloud and rely on volatile memory.

• With this type of memory, if the power is turned

off, the information is retained. If the cloud and

electronic devices operated on non-volatile

memory, $6 billion in electricity costs would be

saved in the U.S. annually.




Smart cards use ferroelectric memories. They can hold relatively large

amounts of information and do not wear out from use, as magnetic strips do,because they use contactless radio frequency input/output. These cards are

the size and shape of credit cards but contain ferroelectric memory that can

carry substantial information, such as its bearer's medical history for use by

doctors, pharmacists and even paramedics in an emergency. Current smart

cards carry about 250 kilobytes of memory.



Tunable Microwave Devices / Optical Waveguides

-100 -75 -50 -25 0 25 50 75 100

0

500

1000

1500

2000

2500

D i e l e c t r i c c o n s t a

n t

3 3

/ 0

Electric Field, E 3 [kV/cm]

(E =0)

Innovative mobile communication

applications is driven by the

combination of different functionalities

as cell phones, GPS, Bluetooth, and

WLAN at varying carrier frequencies

and band widths in a single device.

The use of integrated microwavecomponents with characteristics

tunable by an applied voltage is a

suitable strategy to meet the required

challenges.

P l i D /S



• PIR sensors allow you to sense motion, almostalways used to detect whether a human hasmoved in or out of the sensors range.

Pyroelectric Detectors/Sensors

• The PIR sensor itself has two slots in it each slot is made of a



• The PIR sensor itself has two slots in it, each slot is made of aspecial material that is sensitive to IR.

• When the sensor is idle, both slots detect the same amount of IR,the ambient amount radiated from the room or walls or outdoors.When a warm body like a human or animal passes by, it first

intercepts one half of the PIR sensor, which causes a positivedifferential change between the two halves. When the warm bodyleaves the sensing area, the reverse happens, whereby the sensorgenerates a negative differential change. These change pulses arewhat is detected.

All Ferroelectric materials are Piezoelectric



All Ferroelectric materials are Piezoelectric,

But all Piezoelectric materials are not

Ferroelectric!

Ferroelectrics are spontaneously polarised, but are

also piezoelectric, in that their polarisation changes

under the influence of a stress. This is because

while all ferroelectrics are piezoelectric, not all

piezoelectrics are ferroelectric.



Any Questions?



Thank You

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ferroelectric and piezoelectric materials

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