Description of materials

1. Dielectric ,Piezoelectric and Ferroelectric materials
AVANEESH MISHRA (Y16273033 )
M.Sc IIIrd sem Department of Physics
Dr Harisingh gour University Sagar M.P
Presented by:-

2. Contents
Dielectric Material
Polarization
Piezoelectric Material
Polyvinylidene fluoride
Applications of piezoelectric material
Ferroelectrics

3. 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.
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

4. • 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).

5. Cetro-Symmetric Piezoelectrics
(Non-CentroSymmetric)
Non-pyroelectrics Pyroelectrics
Non-Ferroelectrics Ferroelectrics
Dielectrics
Don’t Posses
Inversion centre
A Hierarchical Overlook

6. 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.

7. Direct Piezoelectric Effect
• Piezoelectric Material will generate electric potential 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 a
voltage with the same polarity as thematerial
Tension
Effect: Increase in volume and it has a voltage
with opposite polarity as the material

8. 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.

9. 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.
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.

10. Naturally occurring crystals:
Berlinite (AlPO4), cane sugar, Quartz, Rochelle salt,
bone (apatiteTopaz, Tourmaline Group Minerals, and dry
crystals)
orthophosphate (GaPO4), LangasiteGallium
(La3Ga5SiO14)
Man-made ceramics:
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
Polymers:
Polyvinylidene fluoride (PVDF)
Piezoelectric material
Man-made crystals:

11. Polyvinylidene fluoride
• 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 PVDF with itsof nanotubes, thus
mechanicalinherent superior
upgraded with nano-technology
properties when
produces a new
generation of piezopolymer, which are durable and can
generate large quantity of electricity economically.

12. 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 nanotubesimpregnation)
 Volume resistivity: 2x1014 ohm-cm;
 Dielectric constant at 60 Hzs: 8.40 pm/V
 Piezoelectric stress constant: 0.23V/ (m. pa)

13. Sonic and Ultrasonic Applications
• Sonar with Ultrasonic time-
domain reflectometers.
• Materials testing to detect
flaws inside cast metals
and stone objects.
elasticity or
in gases and
• Measure
viscosity
liquids
• Used in Compact sensitive
and guitarmicrophones
pickups.
• Loudspeakers.

14. Pressure Applications
• 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
sensors.
• Transducers are used in electronic drum
pads to detect the impact of the
drummer's sticks.
• Energy Harvesting from impact on the
ground
• Atomic force and scanning tunneling
microscopes.
• Electric igniters and cigarette lighters

15. Motor Applications
• 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
frequency.
• The piezo motor is viewed as a high-
precision replacement for the
stepper motor.
used for• Traveling-wave motors
auto-focus in cameras.

16. Ferroelectrics
 All Ferroelectric materials exhibit Piezoelectric effect because –
lack of symmetry.
 Special Class of Piezoelectric Material- exhibit certain other
characteristics also.
 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
Rochelle salt.
 In ferroelectrics, the polarization can be changed and even
reversed by an external electric field.

17. 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 applied
electrical field.
High strain response to applied electrical field
piezoelectricity
Strong variation in polarization with temperature
pyroelectricity

18. 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:
PE
• As E is increased, we start to flip domains and
rapidly increase P.
• When all domains are switched, we reach
saturation.
What happens if the E-field is now removed?

19. Spontaneous Polarization

20. zero field is termed the remnant• The value at
polarisation.
• The value of P extrapolated back from the
saturation limit is the spontaneous polarisation.
• Reversal of the field will eventually remove all
polarisation
– The field required is the coercive field.
• Further increasing the reverse field will completely
reverse the polarisation, and so a hysteresis loop is
formed…

21. Phase Transition
Charges CoincideCharges doesn’tCoincide
> 120°C< 120°C

22. Pyroelectric Materials
A special class of material which is subset of
piezoelectric 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 reaches
electric breakdown before it can get polarized. But
When temperature is changed the polarization of
crystal changes. e.g LiNbO3

23. Pyroelectricity
0.5
0.6
o
TC=490 C
SpontaneousPolarization(C/m2)
0.4
PbTiO3
0.3
0 100 200 300 400 500
Temperature [o
C]
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
p   D  PS
 E

T T

24. Applications of Ferroelectrics
•Non-Volatile RAMs (memory)
•Dynamic Capacitors.
•Tunable Microwave Devices
•Pyroelectric Detectors/Sensors
•Optical Waveguides

25. 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.