dielectric property of chromium oxide nanoparticles

1. Dielectric Properties of Cr2O3 Nanoparticles
BY:
Gaurav Kumar Yogesh
Reg. No. CUPB/M.Sc./SBAS/PMS/2013-14/01
Supervisor: Dr. Kamlesh Yadav
(Assistant Professor)
Centre For Physical And Mathematical Sciences
Central university of Punjab, Bathinda
M.sc. physics (weekly seminar)

2. Content
 Introduction
 Terminology
 Types of polarisation of dielectric
 Complex permittivity
 Dielectric loss
 Dielectric property of Cr2O3 nanoparticles
 Applications
2
4/9/2015

3. Introduction
 Dielectric material is a substance that is a poor conductor of electricity but efficient
supporter of electrostatics field.
 Dielectric material has high polarizibility.
 Dielectric material is the electrically insulator and polarise in the applied field.
 The molecule slightly displaced from the equilibrium and creates an internal field
which decrease the overall field inside the material.
 Dielectric properties concern with storage and dissipation of electric and magnetic
energy in material.
 Dielectric properties studied in the electronic, optics and solid state physics.
 Dielectrics may be sub-divided into two groups :
 Non-Polar : which does not possess the permanent dipole moment.
 Polar: In which the molecules or atoms possess a permanent dipole moment
which is ordinarily randomly oriented, but which become more or less oriented by
the application of an external electric field.
3
4/9/2015

4. Contd.
 Polarisation is directly relating to the induced electric field.
 P = χeЄo E
 Electrical susceptibility of material related to the electrical permittivity
 χe = Єr ˗ 1
 χe = 0, in case of vacuum
 The electric displacement is related to the
polarisation vector as:.
D = Єo E + P = (1 + χe ) Єo E ,
D = Єo Єr E
Where E is average electric field inside the
material.
4
4/9/2015
Fig. Polarisation of dielectric
in the external field

5. Terminology
 χe is the electric susceptibility of the
material, which measure how easily a
material can polarise.
 Єo is the electrical permittivity of
free space.
 Є is the electrical permittivity of the
medium
 Єr is the relative permittivity of the
medium
 P is the polarisation of the material.
 E is the average electrical field of the
material.
5
4/9/2015
Fig. Polarisation of dielectric
inside the external field

6. Types of polarisation of dielectric
 The type of polarization on a microscopic scale is determined by the material.
Most materials exhibit polarization only in the presence of an external field. A
few however show permanent polarization:
 Ferroelectric: crystals exhibit spontaneous permanent polarization.
 Electrets : become permanently polarized if allowed to solidify in the
presence of a strong electric field.
 The type of polarization may be additionally subdivided into the following
categories :
 Electronic: a displacement of the electronic cloud w.r.t the nucleus
 Ionic: separation of +ve and -ve ions in the crystal.
 Orientational: alignment of permanent dipoles (molecules).
 Space-charge: free electrons are present, but are prevented from moving by
barriers such as grain boundaries - the electrons "pile up".
6
4/9/2015

7. 4/9/2015
7
Electronic polarisation
ionic
polarisation
Orientational polarisation
Space charge polarisation
Contd....

8. Complex Permittivity
 Normal material response to the external field depends on the frequency of
applied field.
 The frequency dependence material reflects that polarisation is not
instantaneous.
 For that reason permittivity is the function of the angular frequency or complex
quantity.
 Do e-iωt = є(ω) Eo e-iωt
 Response of material at low frequency limit is called the static frequency limit.
 At high frequency limit, the complex permittivity commonly referred as the є͚ ,
at the plasma frequency and above the dielectric behave as the ideal metals, with
electron gas behaviour.
 As the frequency increases, measurable phase difference is introduced between
the D & E.
 є(ω) = Do / Eo = є e-iδ
 δ is the loss angle
8
4/9/2015

9. Dielectric Loss
 Loss of energy that goes into heating a dielectric material in a varying electric
field.
 Capacitor incorporated in an alternating-current circuit is alternately charged and
discharged each half cycle.
 During the alternation of polarity of the plates, the charges must be displaced
through the dielectric first in one direction and then in the other, and overcoming
the opposition that they encounter leads to a production of heat through dielectric
loss.
Fig. Dielectric loss in dielectric
9
4/9/2015

10. Loss Tangent
4/9/2015
10
 It is defined as the ratio of ratio of the imaginary part of the dielectric constant
to the real part.
 D denotes dissipation factor.
 Q is quality factor.
 “quality factor or Q-factor” is used
with respect to an electronic microwave
material.
 which is the reciprocal of the loss
tangent. For very low loss materials.
Fig. Loss tangent of dielectric

11. Dielectric Properties of Cr2O3 Nanoparticls
 Capacitance of capacitor can be altered by varying the dielectric properties.
 Cr2O3 can also be used as an efficient gate-dielectric-material because it shows
wide band gap, high melting temperature and high oxidation resistance, which is
the essential requirement for a material to be used as gate-oxide materials.
 Frequency dependent dielectric constant Єr of Cr2O3 nanoparticles is wide
range of frequency region (100 Hz – 30 MHz)
 Value of Єr decreases with increase in frequency.
 Higher value of Єr at lower frequency because of
the all kinds polarisation contributes such as dipolar,
Ionic, electronic and space charge.
Fig. Frequency dependent dielectric
constant of Cr2O3 nanoparticles
11
4/9/2015

12. 4/9/2015
12
Applications of Dielectric Loss
 Industrial coatings such as parylen provide a dielectric barrier between the
substrate and its environment.
 Mineral oil is used extensively inside electrical transformers as a fluid dielectric
and to assist in cooling.
 For drying lumber and other fibrous materials, for preheating plastics before
molding, and for fast jelling and drying of foam rubber.
 Piezoelectric materials are another class of very useful dielectrics.
 Dielectric fluids with higher dielectric constants, such as electrical grade castor
oil, are often used in high voltage capacitors to help prevent corona discharge
and increase capacitance.

13. THANK YOU
4/9/2015
13