The thermoelectric effect is the direct conversion temperature difference into electricity

1. Anandhu Thampi
M.Sc Physics
Cochin university of science and technology
Cochin-22

2.  The thermoelectric effect is the direct conversion of
temperature difference into electric voltage and vise versa
 In a thermoelectric material there are free carriers which
carry both charge and heat.

3.  In the 1820’s Thomas Seebeck (Germany) discovered that if
two metals at different temperatures were touching could
create an electric current.
 In 1834, Jean Peltier (France) discovered that an electrical
current would produce heating or cooling at the junction
of two dissimilar metals.
 In 1851, Lord Kelvin discovered that when the current
flows through the unequally heated conductor, heat is
evolved or absorbed through the conductor

4. Thomas Johann
Seebeck
Jean Charles
Athanase Peltier
William Thomson(
Lord Kelvin)
Abram F. Ioffe H. Julian Goldsmid
1821 1834
1854 1928
1954
1851
Gustav Magnus

5. 1930 1959 1959 1970
1998 1999
Radio Home refrigerator
Radioactive
Thermoelectric
Generator (RTG)
Cardiac
pacemaker
Seiko introduces the
Thermic watch
Seat coolers in the
Lincoln Navigator and
Toyota's Lexus
Voyager 1
1977

6.  Thermoelectricity - known in physics as the
"Seebeck Effect“
 Thomas Johann Seebeck found that a circuit
made from two dissimilar metals, with
junctions at different temperatures would
deflect a compass magnet.
 Discovered a small current flow and so
demonstrated that heat could be converted to
electricity.

7. When the junctions of two
different metals are maintained
at different temperature, the emf
is produced in the circuit This is
known as Seebeck effect.
 The conductor 1 is maintained
at T+∆T temperature
The conductor 2 is maintained at
temperature T
Since the junctions are
maintained at different
temperature, the emf ‘U’ flows
across the circuit

9.  The heating or cooling at
an electrified junction of
two different conductors
 The Peltier heat
generated at the junction
per unit time
 The peltire coefficient
represents how much heat
is carried per unit charge

10.  The current flows through
the unequally heated
conductor, heat is evolved or
absorbed through the
conductor
 Heat production rate unit per
unit volume q´=-KJ•∇T
 K- Thomson coefficient
 ∇T- Temperature gradient
 J- Current density

11.  Positive Thomson effect
 Current flows from lower T to high T, heat is absorbed throughout
the conductor
 Eg:- Sn, Au, Ag, Zn, Cd, Sb
 Negative Thomson effect
 Current flows from lower T to high T heat is liberated throughout
the conductor
 Eg:- Bi, Ni, Pt, Co, Hg
 Nill Thomson effect
 Current flow from high T to Low T or Low T to high T heat is
neither liberated nor absorbed
 Eg:- Pb

12.  The good thermoelectric
materials should possess
1. Large Seebeck
coefficients
2. High electrical
conductivity
3. Low thermal
conductivity
 Ѕ – Seebeck coefficient
 σ – Electrical conductivity
 Κ – Thermal conductivity
 Т - Temperature

13.  maximum efficiency of a
thermoelectric material
depends on two terms
 Carnot efficiency, for all
heat engines can not
exceed Carnot efficiency
 Depends on the
thermoelectric properties,
Seebeck coefficient,
electrical resistivity and
thermal conductivity

15.  Direct band gap
semiconductor
 Indirect band gap
semiconductor

16. The first Brillouin zone of
bismuth telluride

17.  The fermi level should be
a little below (n type) or
above (p type) the band
edge.
 Maximize the no. of
channels in the fermi
window (large effective
mass).
 Maximize the velocity
(small effective mass).
 Minimize scattering (small
DOS – small effective
mass)

18.  The conduction band
minimum and the valance
band maximum are both
at the Γ point making it a
direct band gap, with a
size of 0.33 eV

19.  The conduction band
minimum is now between
the Γ and the Z points and
the valance band
maximum is now between
the Z and F points,
because they are not at
the same k point the band
structure now has an
indirect band gap, with a
size of 0.11 eV

20.  Darbble et.al introduced six valley model
 Highest valence band and lowest conduction band have six
valleys
 Bands are described in terms of effective mass tensor
 All valleys with the extrema inside first brillouin zone
 Multi valley band structure shows good thermoelectric
properties

21.  A thermoelectric module
is an array of
thermocouples connected
electrically in series but
thermally in parallel
 Many couples are used (in
both power generation
and cooling) becuause the
voltage drop across one
couple is only on the order
of millivolts

22.  The Seebeck voltage of the
couple, S is derived from the
Seebeck coefficient of the n-
type and p-type elements
and the number of couples, n
 The electrical resistance of
the device depends on
electrical resistance of the
thermoelectric, electrical
resistnace of the metal
interconnects & contact
resistance between the
interconnects and the
thermoelectric materials

23.  The total thermal
conductance
 Kl is the parallel thermal
loss per couples
associated with gas
conduction, radiation, or
other losses

24.  Environmental friendly
 Recycles wasted heat energy
 Reliable source of energy
 scalability
 Lower production cost
 Silent in operation
 Simple, compact & safe

25.  Low energy conversion efficiency
 Requires relatively constant heat source
 Slow technology progression

26.  Thermoelectric generator
 Cooling Computers
 Drink Coolers
 Recharging Devices
 Space Probes
 Solar Power
 Low power remote controller system
 Nuclear power stations
 Automotive TEGs

28. 1. H. Julian Goldsmid:, Introduction to Thermoelectricity,
Springer international publisher,2010
2. J.appl.phys.111,113707(2012)
3. M G Kanatzidis etal:, Chemistry,physics,and material
science of thermoelectric materialsn beyond bismuth
telluride, First edition, Springer international publisher,
2003
4. http://thermoelectrics.matsci.northwestern.edu/therm
oelectrics.html
5. Liouise Henderson:, Calculating crystal properties of
bismuth telluride using wien22, senior thesis,2014

29. THANK YOU