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Space probe to the Jupiter From JPL, NASA Radioisotope
Thermoelectric Generator (PbTe)
Introduction to Thermoelectric Materials and Devices
10th Semester of 2012 2012.05.31, Thursday Department of Energy Science Sungkyunkwan University
1 Thermoelectric Phenomena and Conversion Efficiency
2 Thermoelectric Transport Theory I : Electrical Properties
3 Thermoelectric Transport Theory II : Thermal Properties
4 Measurement of Thermoelectric Properties
5 Materials Preparation : Bulk
6 Materials Preparation : Thin Film
7 Thermoelectric System : Current and Future of Module
8 Applications : Power Generation and Heat Cooling
9 Thermoelectric Materials : State-of-the-art
10 Thermoelectric Materials : Intermetallics
11 Thermoelectric Materials : Oxides
12 Thermoelectric Materials : Phonon Glass and Electron Crystal (PGEC) Materials
13 Theory and Modeling in Nanostructured Thermoelectrics
14 High efficiency in Low Dimensional Materials
15 Hybrid Energy Conversion Systems of Thermoelectrics
16 Final Exam
Plan
Snyder, Toberer, Nat. Mater. 2008
Thermoelectric Research : Current and Future of Module
Target : High Conversion Efficiency of Thermoelectric Devices
Module : Accumulation of Elements, Contact Resistance (Welding), Shape Diversity for Micro-Scale (Thin Film)
System : Circumstance Suitability (Generation), Diversity of Mass Conversion System, Hybridization with other renewable energy system
Materials : High Efficiency (High ZT), New Materials and Various Categories (Limitation to Heavy Metal Compounds), Properties for Hybridization (Magnetic Semiconductor for Magnetocaloric) (Low Workfunction for Thermionic)
Thin Film
Cascade Conventional
Solar absorber + TE Custom Cooling Device D. Kraemer et al., Nat. Mater. 20011
Intermetallic Compounds : Definition
Definition Intermetallic compounds as solid phases containing two or more metallic elements, with optionally one or more non-metallic elements, whose crystal structure differs from that of the other constituents Intermetallic compounds are often simply called “Alloys” Both are metallic phases containing more than one element, but… In alloys, the various elements substitute randomly for one another in the crystal structure, forming a solid solution with a range of possible compositions, while… In intermetallic compounds, different elements are ordered into different sites in the structure, with distinct local environments and often a well-defined, fixed stoichiometry
Properties Intermetallic compounds are generally brittle and high melting. They often offer a compromise between ceramic and metallic properties when hardness and/or resistance to high temperatures is important enough to sacrifice some toughness and ease of processing.
Examples Some examples include alnico (Al-Ni-Co) and the hydrogen storage materials in nickel metal hydride batteries. Ni3Al, which is the hardening phase in the familiar nickel-base superalloys, and the various titanium aluminides have also attracted interest for turbine blade applications, while the latter is also used in very small quantities for grain refinement of titanium alloys.
Silicides, intermetallics involving silicon, involving many of the elements have been studied for, and some utilized as, barrier and contact layers in microelectronics.
Intermetallic Compounds
Laves phases Zintl phases
That have composition AB2. The phases are classified on the basis of geometry alone. There are three different classification classes: cubic MgCu2 (C15), hexagonal MgZn2 (C14), and hexagonal MgNi2 (C36). In general, the A atoms are ordered as in diamond, hexagonal diamond, or a related structure, and the B atoms form tetrahedra (AB4)around the A atoms for the AB2 structure. Laves phases are of particular interest in modern metallurgy research because of characteristic features that are the almost perfect electrical conductivity, but they are not plastically deformable at room temperature.
The product of a reaction between group 1 (alkali metals) or group 2 (alkaline earths) and post transition metals from group 13, 14, 15 or 16.
Zintl phases are a subgroup of brittle, high melting point intermetallic compounds which are diamagnetic or exhibit temperature-independent paramagnetism, are poor conductors or semiconductors.
NaTl, where it is now known that the structure consists of a polymeric anion (-Tl−-)n with a covalent diamond structure with Na+ ions fitted into the anionic lattice. NaSi where the polyanion is tetrahedral (Si4)4− similar to phosphorus molecule P4. Na2Tl which the polyanion is tetrahedral (Tl4)8− similar to phosphorus molecule P4.
FeSi2
Phase Diagram
FeSi2
According to the phase diagram of the binary system Fe–Si, the stoichiometric FeSi2 solidifies at 1493 K as a eutectic structure composed of -Fe2Si5 and -FeSi which are metallic phases with poor thermoelectric properties. The -FeSi2 phase formation is either through the peritectoid reaction between -Fe2Si5 and -FeSi or the eutectoid decomposition of -Fe2Si5 to -FeSi2 and Si. It is well known that -FeSi phase generally remains stable after normal fabrication procedure and that the transformation from -Fe2Si5 to -FeSi2 phase by heat treatment is very sluggish.
FeSi2
FeSi2
FeSi2
0.1 nm 1nm 10 nm 100 nm
Phonon distribution
Phonon wavelength
Deteriorate electrical conductivity
Point defect; doping, intercalation
Incoherent interface; grain boundary, nano-dispersion
Semi-coherent
(strained) interface; misfit dislocation
Coherent interface
FeSi2
CoSi compound
Zn4Sb3
Zn4Sb3
Half-Heusler : TiNiSn
Half-Heusler : TiNiSn
Thermal Conductivity
300 400 500 600 700 800 900 1000
3
4
5
6
7
8
9
10
11
TiNi0.9
Pt0.1
Sn
TiNi0.95
Pt0.05
Sn
Ti0.9
Zr0.1
NiSn
Ti0.9
Hf0.1
NiSn
TiNiSn
TiNiSn0.9
Si0.1
TiNiSn0.95
Si0.05
Therm
al C
onductivity (
W/m
K)
Temperature (K)
The Most Effective Element is Hf
300 400 500 600 700 800 900 1000
3
4
5
6
7
8
9
TiNi0.9
Pt0.1
Sn
TiNi0.95
Pt0.05
Sn
Ti0.9
Zr0.1
NiSn
Ti0.9
Hf0.1
NiSn
La
ttic
e T
he
rma
l C
on
du
ctivity (
W/m
K)
Temperature (K)
TiNiSn
TiNiSn0.9
Si0.1
TiNiSn0.95
Si0.05
Lattice Thermal Conductivity
Ti (MTi=48) : Hf (MHf=179) and Zr (MZr=91)
Hf
CsBi4Te6
CsBi4Te6
Yb14MnSb11
Yb14MnSb11
Yb14MnSb11
Enhancement of DOS(E)
well
barrier
Confinement of conduction
electrons leads to enhancement
of DOS(E)
m
knnn
LmE zyx
2)()
2(
2
22
22222
)(2
3)1
(znynxn
Li zyx
eL
dkkm
dE2
2 dE
k
mdk
12
dkkL
L
dkkdkkN
2
33
3
2
22
4)(
Density of State
32 ,)/1(/)(2 LVkdkkVdkkN ][)2(
2
1)( 132/1
3
2/3 eVcmdEE
mdEEN
3-dimensional system
222
22
222
2222
)(22
)(2
)()2
(2
z
z
z
z
yx nLm
km
nLm
nnLm
E
znL
e z
z
ynxnL
i yx
sin)(
2
dkkm
dE2
2 dE
k
mdk
12
kdkL
L
kdkdkkN
22
2)(
3
3
Density of State
2,//)(2 LSkdkSdkkN ][1
)( 12
2
eVcmdEm
dEEN
2-dimensional system
)()(2
)2
(2
222
,
222
2
zy
zy
x nnLm
nLm
E
zn
Lyn
Le z
z
y
y
xnL
i x
sinsin2
dkkm
dE2
2 dE
k
mdk
12
kdkL
L
dkdkkN
22)(
Density of State
//)(2 dkLdkkN ][1)2(
2
1)( 11
2/12
2/1 eVcmdE
E
mdEEN
1-dimensional system
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