This PPT gives introduction to Dielectrics, Piezoelectrics & Ferroelectrics Materials, Methods and Applications. A quick glance at the dielectric phenomena, symmetry, classification, modelling, figures of merit and applications. Comprehensive overview of the physics and applications of ferroelectric

1. Dielectrics, Piezoelectrics &
Ferroelectrics
Materials, Methods and
Applications

2. Outline
• Dielectrics and dielectric polarization
• Dielectrics -> Piezoelectrics -> Pyroelectrics -> Ferroelectrics
• Ferroelectric phenomena and properties
• Measurement of spontaneous polarization
• Classification of ferroelectrics
• Application of ferroelectrics

3. Dielectrics
Dielectric is an electrical insulator which can be
polarized on application of external electric filed.
They do not conduct electricity due to the very low density
of free charge carriers. Here, the electrons are bound to
microscopic regions within the material, that is the atoms,
molecules, or clusters.
D  0 E  P  0 E  0 E  0 (1 )E  0 E
Polarization is defined as dipole moment per unit volume. It
modifies dielectric function of a vacuum, for example to
increase the capacity (i.e. the ability to store charge) of
capacitors.
1. Electronic Polarizability
2. Ionic Polarizability
3. Dipolar Polarizability
4. Space Charge Polarizability

4. Applications

5. Polarization is the separation of a positive and a negative
charge barycenter of bound charges. If this separation is
induced by an applied electric field, it is called dielectric
polarization.
If the separation is induced by an applied strain field, it is
called piezoelectric polarization.
Several dielectric crystals exhibit a spontaneous
polarization below a critical temperature which is related
to a change in crystal symmetry.
A spontaneous polarization in the material leads to
pyroelectric effects under temperature changes.
Ferroelectricity is obtained when the orientation of
polarization can be reoriented between
crystallographically equivalent configurations by an
external field.
Piezoelectrics, Pyroelectrics & Ferroelectrics

6. Ferroelectric Materials: A ferroelectric material is a material
that exhibits, over some range of temperature, a
spontaneous electric polarization that can be reversed or
reoriented by application of an electric field
Ferroelectricity
Domain is a region in which all the individual dipoles
point in a particular direction
Barium titanate is a prototype perovskite
ferroelectric
Perovskite general formula: ABO3
In barium titanate Ba2+ occupies A site (corner
of cube)O2-occupies face centre and Ti4+
occupies body centre
Dipole moment of a unit cell arises from Ti4+ off-
centering

8. Measurement of Spontaneous Polarization
Sawyer-Tower circuit :

9. Temperature dependence of the spontaneous polarization and permittivity in a ferroelectric
material. (a)–(f) indicate the temperature ranges for each application.
Temperature dependence of electrical properties of a ferroelectric
Night vision

10. Ferroelectricity: Two main classes of ferroelectrics
Ex: NaNO2 ,KDP
Ex: ionic crystals with perovskite,
or ilmenite structure.
Based on the origin of
spontaneous Polarization

11. Ferroelectric Materials can be structurally categorized into 4 groups:
1. Corner Sharing Octahedra:
1. Perovskite-Type Compounds
(such as BaTiO3, PT, PZT, PMN, and PLZT)
2. Tungsten-Bronze-Type Compounds (such
as PbNb2O6)
3. Bismuth Oxide Layer Structured Compounds (such
as Bi4Ti3O12 andPbBi2Nb2O9)
4. Lithium Niobate and Tantalate (such as LiNbO3 andLiTaO3)
2. Compounds Containing Hydrogen Bonded Radicals (such as
KDP, TGS, and Rochelle Salt)
3. Organic Polymers (such as PVDF and co-polymers)
4. Ceramic Polymer Composites (such as PZT-PE)
Types of Ferroelectric Materials
Perovskite (BaTiO3) LiNbO3
Polyvinylidene fluoride (PVDF)

12. Ferroelectric properties
 Most ferroelectric materials undergo a structural phase transition from a high-temperature nonferroelectric
(or paraelectric) phase into a low-temperature ferroelectric phase.
 The symmetry of the ferroelectric phase is always lower than the symmetry of the paraelectric phase.
 The temperature of the phase transition is called the Curie point, TC.
 Above the Curie point the dielectric permittivity falls off with temperature
 according to the Curie–Weiss law
 where C is the Curie constant, T0 (T0 ≤TC) is the Curie–Weiss temperature
 Some ferroelectrics, such as BaTiO3, undergo several phase transitions
 into successive ferroelectric phases.

13. Ferroelectrics have very high dielectric constants at
relatively low applied field frequencies. Capacitors
made from these materials can be significantly
smaller than capacitors made out of other
dielectric materials.
The combined properties of memory,
piezoelectricity, and pyroelectricity make
ferroelectric capacitors some of the most useful
technological devices in modern society.
Ferroelectric capacitors are at the heart of medical
ultrasound machines, high quality infrared cameras,
fire sensors, sonar, vibration sensors, and even fuel
injectors on diesel engines.
Hysteresis means memory and ferroelectric
capacitors are used to make ferroelectric RAM for
computers and RFID cards.
The electro-optic modulators that form the
backbone of the Internet are made with
ferroelectric materials.
Applications of Ferroelectrics

14. Ferroelectricity: Landau-Ginzburg phenomenological theory
Free energy Order parameter (polarization) Electric field
F 
1
aP2

1
bP4

1
cP6
 ... EP
2 4 6
To find the equilibrium solution we need to find the
minima of FP by solving the equation:
Ignoring higher terms we can get the linear solution:
F
 0
P
F
 aP  E  0
P
 
P 
1
E a
All the coefficients of polarization have temperature
dependence. The dependence of a on temperature can
be approximated as: a =
𝑻−𝑻𝒄
𝑪
Х =
𝑪
𝑻−𝑻𝒄
Curie Weiss Law