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Piezoelectric and Ferroelectric materials
Some Basic Terms
• Dielectric Material- The Cumulative effect of microscopic displacements
(charges,ions,electrons) results in Net Polarization due to setting up of
induced dipole moments or due to rotation of permanent electric dipoles
which 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.
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).
A Hierarchical Overlook
Cetro-Symmetric Piezoelectrics Inversion centre
The History of Piezo
• The name Piezo originates
from the Greek word
piezein, which means to
squeeze or press.
• The piezoelectric effect was
first proven in 1880 by the
brothers Pierre and Jacques
What is Piezoelectric Material?
Piezoelectric Material is one that possesses the property of
converting mechanical energy into electrical energy and vice
Piezoelectric materials can be divided in 2 main groups:
crystals and cermaics.
Direct Piezoelectric Effect
• Piezoelectric Material will generate electric
potential when subjected to some kind of
• The direct Effect : Strain Sensor, microphones,
gas lighters, ultrasonic detectors
Effect: Decrease in volume and it has a Effect: Increase in volume and it has a voltage
voltage with the same polarity as the material with 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 If the applied voltage has the opposite
then the material expands. 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 1/20th 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
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
Gallium orthophosphate (GaPO4), Langasite
Barium titanate (BaTiO3), Lead titanate (PbTiO3), Lead
zirconate titanate (Pb[ZrxTi1-x]O3 0<x<1) - More commonly
known as PZT, Potassium niobate (KNbO3), Lithium niobate
(LiNbO3), Lithium tantalate (LiTaO3), Sodium tungstate
(NaxWO3), Ba2NaNb5O5, Pb2KNb5O15
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 frequency
standards in watches, electronic clocks, computer
• In 1961 polyvinylidene fluoride, a piezoelectric plastic
was invented. It is one of the most widely used
piezopolymer from which substantial electricity can be
generated. It is cheap and physically quite strong.
• In 2001 researchers found that PVDF becomes
supersensitive to pressure when impregnated with very
small quantity of nanotubes, thus PVDF with its
inherent superior mechanical properties when
upgraded with nano-technology produces a new
generation of piezopolymer, which are durable and can
generate 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 or
• 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: 154-1840 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-
• Materials testing to detect
flaws inside cast metals
and stone objects.
• Measure elasticity or
viscosity in gases and
• Used in Compact sensitive
microphones and guitar
• Transient pressure measurement to
study explosives, internal combustion
engines (knock sensors), and any other
vibrations, accelerations, or impacts.
• Piezoelectric microbalances are used as
very sensitive chemical and biological
• Transducers are used in electronic drum
pads to detect the impact of the
• Energy Harvesting from impact on the
• Atomic force and scanning tunneling
• Electric igniters and cigarette lighters
Consumer Electronics Applications
• Quartz crystals resonators as
frequency stabilizers for
oscillators in all computers.
• Phonograph pick-ups
• Accelerometers: In a
piezoelectric accelerometer a
mass is attached to a spring that
is attached to a piezoelectric
crystal. When subjected to
vibration the mass compresses
and stretches the piezo electric
• Piezoelectric elements can be used
in laser mirror alignment, where
their ability to move a large mass
(the mirror mount) over microscopic
distances is exploited. By
electronically vibrating the mirror it
gives the light reflected off it a
Doppler shift to fine tune the laser's
• The piezo motor is viewed as a high-
precision replacement for the
• Traveling-wave motors used for
auto-focus in cameras.
All Ferroelectric materials exhibit Piezoelectric effect because –
lack of symmetry.
Special Class of Piezoelectric Material- exhibit certain other
Exhibit spontaneous polarization i.e., polarization in the
absence of an electric field.
Ferroelectrics are the electric analog of the ferromagnets, which
may display permanent magnetic behaviour.
Valasek discovered the first ferroelectric material, namely
In ferroelectrics, the polarization can be changed and even
reversed by an external electric field.
Spontaneous polarization in the absence applied
Extremely high dielectric constant (~500-15,000).
Strong non-linear dielectric response to an applied
High strain response to applied electrical field
Strong variation in polarization with temperature
Polarisation vs. E-field
• If we apply a small electric field, such that it is not
able to switch domain alignments, then the
material will behave as a normal dielectric:
• As E is increased, we start to flip domains and
rapidly increase P.
• When all domains are switched, we reach
What happens if the E-field is now removed?
• The value at zero field is termed the remnant
• The value of P extrapolated back from the
saturation limit is the spontaneous polarisation.
• Reversal of the field will eventually remove all
– The field required is the coercive field.
• Further increasing the reverse field will completely
reverse the polarisation, and so a hysteresis loop is
Perovskite Crystal Structure
General Formula: ABX3
A special class of material which is subset of
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 reaches
electric breakdown before it can get polarized. But
When temperature is changed the polarization of
crystal changes. e.g LiNbO3
Spontaneous Polarization (C/m2)
0 100 200 300 400 500
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.
p S E
T E T T
Non-Volatile RAMs (memory)
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 very
expensive 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.
Non-Volatile RAMs (memory)
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
Dielectric constant 33/0
Innovative mobile communication
applications is driven by the
(E=0) combination of different functionalities
-100 -75 -50 -25 0 25 50 75 100
Electric Field, E3 [kV/cm] as cell phones, GPS, Bluetooth, and
WLAN at varying carrier frequencies
and band widths in a single device.
The use of integrated microwave
components with characteristics
tunable by an applied voltage is a
suitable strategy to meet the required
• PIR sensors allow you to sense motion, almost
always used to detect whether a human has
moved in or out of the sensors range.
• The PIR sensor itself has two slots in it, each slot is made of a
special 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 positive
differential change between the two halves. When the warm body
leaves the sensing area, the reverse happens, whereby the sensor
generates a negative differential change. These change pulses are
what is detected.
All Ferroelectric materials are Piezoelectric,
But all Piezoelectric materials are not
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.