1
Nanocomposites and Nanothermoelectrics
Wenqing Zhang(张文清 ), Lidong Chen(陈立东 )
Shanghai Institute of Ceramics, Chinese Academy of Sciences
Shanghai, China
Oct 17, 2009
Basic principle of thermoelectrics (TE)Basic principle of thermoelectrics (TE)
max
1 1
1
h c
h h c
T T ZT
T ZT T T
Th
Tc
ZT
Carnot efficiency
TC TH
S= V / TV
Seebeck effect was discovered in 1821
ZT SLL++ ee)
Insulators Semiconductors Metals
S
n
e
L
S
n ~ 1019 cm-3
S2/
n
LL
ee= =
LLTT
Narrow-gap SemiconductorNarrow-gap Semiconductor
窄带半导体 Eg~(5-10)kBT.
diffusion of hole
high temperature region
(a) Initial stage
low temperature region
T0 T0+TT0
high temperature region
Thermoelectric phenomena of p-type semiconductor
+ -
(b) Under equilibrium
low temperature region
T0 T0+TT0
S= V / T
V
T0+T
T0+TT0
T0
Bulk Mater. ZT ~ 1.0 (1960-1995); ~ 1.0-1.3 (1995- )
热电现象的物理基础热电现象的物理基础Thermoelectrics and Thermoelectrics and ConjugatedConjugated Physical Properties Physical Properties
Timeline of ZTTimeline of ZT
CoSb3: Ce, Ba, Yb, Sm
CoSb3: Ce+Ba, Ce+Ca
CoSb3/C60, ZrNiSn/ZrO2
Bi2Te3-based composite
Clathrate
Bi2Te3/Sb2Te3 SL (RTI)
PbSeTe/PbTe QD (MIT)
Bi2Te3PbTeSi0.8Ge0.2
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1940 1960 1980 2000 2020
FIG
UR
E O
F M
ER
IT (
ZT
) max
YEAR
Narrow Eg:Bi2Te3
PbTeSi0.8Ge0.2
ZT<1.0
CsBiTeYbMnSb
New comp: PGEC, etcComposite: Nano-particle dispersion ZT > 1.0
Low dimension
Multiple filled CoSb3
EC/Electron Crystal: Crystal-like electron
transport PG/Phonon Glass:
Glass-like phonon(thermal) transport
Only realized in compounds with very special crystal structure – caged.
Other systems?
ZT = S2T/(kkLL++ k kee)
Phonon Glass and Electron CrystalPhonon Glass and Electron Crystal
Crystal with intrinsic lattice voids; Impurity partially filling
in the voids.
T (K)
200 400 600 800 1000 1200 1400
ZT
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Bi2Te3
PbTe SiGe
Ba0.24Co4Sb12
Ba0.08Yb0.09Co4Sb12
Triple-filled
Yb0.12Co4Sb12
ZTave = 1.2
• Ba0.08La0.05Yb0.04Co4Sb12.05
Ba0.10La0.05Yb0.07Co4Sb12.16
Multiple-filled Skutterudites –Phonon Glass Electron Crystal Materials with high ZTs
Chen LD, Zhang W, Yang J et al. PRL(2005), PRB(2006,2007),APL(2007,2008,2009), to be submitted (2009)US patents (2007,2008,2009)
7.8Å
System Max ZT Approach Reason
CoSb3-based ~1.7 bulk kL reduction ~ 1.45 nanocomposite
Bi2Te3-based ~ 1.5 thin film nanocomposite kL reduction
PbTe-based(LAST) ~ 1.5 nanocomposite kL reduction
~ 1.5 bulk Enhanced PF
GeTe-based(TAGS) ~ 1.6 nanocomposite kL reduction
Si-Ge-based ~ 1.3 nanocomposite kL reduction Si-nanowire ~ 0.8* nanowire ???
State-of-the-art high ZT materials
kL: Lattice thermal conductivityPF: power factor (=S2
Role of Lower Dimensions in Thermoelectrics
Density of States (DOS) for Low D
ZT 2T
( E L )Large variation of DOS yields large Seebeck Coefficient;
Low dimension yields large dn(E)/dE
ZT ≈ S2≈ S2n
ZT2D ≥ ZT3D2 2 ln
3F
B
E
k TS
e E
FE
DOSS
E
限域效应和界面效应及其协同作用Collective Effects in Nanocomposites: Size and Interfaces
particles
phonons
块状低维复合材料系统Thermoelectric Nanocomposites
声子 (phonon)
电子 (electron)
PGEC:
电热输运规律与调控机制电热输运规律与调控机制Compounds, Size Effects and Interface Effects
Nano Bulk Nanocomposites
11
Bulk Nanocomposite
Bulk nanocomposite : In situ nanoparticle formation plus SPSmelt-spinning(MS) plus SPS Chemical synthesis plus SPSMechanical alloy(MA) plus SPS
SPS : Non-equilibrium
12
CoSb3 Yb+ Yby+xCo4Sb12 YbyCo4Sb12+xYb
Oxidation
Precipitation
YbyCo4Sb12
Yb2O3
SPS
y+x
晶界处纳米颗粒
晶粒内纳米颗粒
In-situ preparation of YbyCo4Sb12/Yb2O3 nano-composites
Chen, Zhang, Appl. Phys. Lett. (2006); J. Appl. Phys. (2005, 2007); China patent
Selective oxidation of Yb leads to the formation of homogeneously dispersed nano-size oxide particles. severed as effective phonon scattering centers.
Grain-boundary
Inside Grain
Using stable partial filler to realize nanocomposite
13
TE performance of YbyCo4Sb12/Yb2O3
L was greatly depressed by the Yb2O3 nano particles dispersed inside grain and on the grain-boundary. ZT ~ 1.3
L was greatly depressed by the Yb2O3 nano particles dispersed inside grain and on the grain-boundary. ZT ~ 1.3
Appl. Phys. Lett. (2007, 2006, 2003); China Patent
ZT
300 400 500 600 700 800 900Temperature (K)
0
0.5
1.0
1.5
y =0.15
y =0.21/Yb2O3
y =0.25/Yb2O3
Nolas
Sales
Anno
ZT=S2T/ZT=S2T/
In-situ formed YbyCo4Sb12/GaSb nano-composites
GaSb: 5-10 nmGrain boundary
& inside grainS also improvedZT > 1.4
Xiong, Chen, Zhang, SICCAS(2009)
Composite Thermoelectric Materials
Energy (meV)
DO
S
3D
Interface effect Key Structural Unit
Electron Atoms Grain MacroCluster
Size effect
Thermoelectric transport at electronic and atomic levels ; Size effects from nano dispersions ; Interface structure and Interface-induced effects ; Correlation between local properties and global
performance.
Design of Nanothermoelectrics
Structure-property relationship study: expt + theory
tot-e(k) : relaxation times for both carrier transport. carrier transport with scattering from phonon and impurities included; no effective way to determine tot (k) yet. Ab initio method to calculate Ab initio method to calculate tot ?? Electron scattering in crystal & composites: Electron scattering in crystal & composites: A very challenge work.
Performance prediction for ThermoelectricsPerformance prediction for Thermoelectrics
30
3
2 2
4(( ( ))) t
dot
fe
kE ke v k
30
3
2
4
1( ) ( )) )( (tot e
f dkfE
eS v k E E
Tk
1. Electronic structure issue: band gap problem. 2. Electrical transport: Power Factor = S2 A. near equilibrium distribution (Boltzmann transport equation)
B. Far from equilibrium transport: still an argument.
3. Thermal transport: Thermal conductivityThermal conductivity
(( Electrical ConductivitElectrical Conductivityy ))
(( Seebeck CoefficienSeebeck Coefficientt ))
ZT = S2T/k
Experimental NanothermoelectricsExperimental Nanothermoelectrics
Realizing homogenous dispersion of nano objects;
Growth and evolution of nano dispersions;
Interface-induced or interface-controlled microstructure formation: dynamics and kinetics
Nonequilibrium formation of nano composites;
Size distribution and performance
Nano composites
Controllable synthesis of nanocomposite materials
Formation & microstrustural evolution of
thermoelectric nanocompsites
Structure characterization and property measurements
Microstructural characterization: 3-dimensional structure
Functionality measurements: Inhomegeneous at atomic scale
Spectroscopy measurement: Hall, electron conductivity, thermal transport, various other spectrum density of states
Energy
DOS
Experimental NanothermoelectricsExperimental Nanothermoelectrics
Detailed microstructure and function characterization;Advanced spectroscopic measurement for electronic structures.
??
Thermoelectric Materials New concepts and search for new materials: theory and expt Nanocomposites: nano- grained, nano- dispersion, texture, … Organic/inorganic composites and organic TE Materials TE films: Bi2S3 , Bi2Te3 etc. Mechanical stability improvement: doping and texture Mess production for industrial applications
Thermoelectric Devices Waste heat recovery and cooling: automobile Special power generation
Research groups invloved Prof. Chen Lidong (composites, devices, and systems) Prof. Zhang Wenqing (new compounds and TE material design) A few chemistry people
Supported by MOST-973, NSFC, CAS, local automobile company, US-Corning, GM
Research on Thermoelectrics in SICCAS
Computational Materials Physics Group
Fundamental Research on Fundamental Research on Energy-conversion MaterialsEnergy-conversion Materials (( 能量载流子的输运及其耦合:电子能量载流子的输运及其耦合:电子 -- 声子声子 -- 离子)离子)
L Xi, Jiong Yang, W Zhang et al., L Xi, Jiong Yang, W Zhang et al., J Am Chem Soc.J Am Chem Soc. (2009) (2009)Jiong Yang, HM Li, WQ Zhang et al., Jiong Yang, HM Li, WQ Zhang et al., Adv. Funct. MaterAdv. Funct. Mater. (2008). (2008)X.Shi, W. Zhang, LD Chen, J. YangX.Shi, W. Zhang, LD Chen, J. Yang,, Phys. Rev. Lett.Phys. Rev. Lett. (2005). (2005).W Zhang, X. Shi, ZG Mei, LD Chen et al., W Zhang, X. Shi, ZG Mei, LD Chen et al., Appl. Phys. Lett.Appl. Phys. Lett. (2006). (2006).ZG Mei, W Zhang, LD Chen et al., ZG Mei, W Zhang, LD Chen et al., Phys. Rev. BPhys. Rev. B 74, (2006) 74, (2006) ;; Phys. Rev. B.
(2008) YZ Pei, LD Chen, W Zhang et al., Appl. Phys. Lett., (2006).J Yang, W. Zhang et al, Appl. Phys. Lett., (2007).X. Shi, W. Zhang, L. D. Chen, et al., X. Shi, W. Zhang, L. D. Chen, et al., Phys. Rev. BPhys. Rev. B, 75, 235208 (2007)., 75, 235208 (2007).X Shi, W. Zhang, LD Chen, Acta Mater. (2008)
Physics and Chemistry at Physics and Chemistry at Interfaces Interfaces (( 界面功能性与复合材料设计:无机界面功能性与复合材料设计:无机 -- 无机界面、无机无机界面、无机 -- 有机界面有机界面 ))
HT Li, W Zhang et al., Acta Mater. (2009).J Feng, W Zhang, et al. , Phys. Rev. Lett. 97, (2006); Phys. Rev. B (2005).W. Zhang et al., Inter. J. Mater. Sci., (2006). W. Zhang et al., Phys. Rev. B 70, 024103 (2004); Phys. Rev. B 67, 542414
(2003).W. Zhang et al., Phys. Rev. Lett. 85,3225,(2000); Phys. Rev. Lett. (1999).W. Zhang et al., Acta Mater. 50, 3803,(2002).
International Conference on Thermoelecrics
ICT’2010, Shanghai, China
Thank you for your attention!
Key scientific issue – size effectsKey scientific issue – size effects
Functions of nano dispersions: electronic structure and phonon spectrum from the localized nano-dispersions; their effects on electrical and thermal transports of the whole nano composites
Research: Microstructure characteristics of nano
dispersions;
Electronic structures of composites with nano dispersions and transport properties; effects from resonant states around Fermi level;
Effect from the atomistic nonhomegeneous materials;
Correlation between local properties and global performance.
Nano dispersions
Quantum Confinement effect:
Seebeck enhancement
Energy (meV)
Ele
ctr
on
DO
S
3D
Key scientific issue – Interface effectsKey scientific issue – Interface effects
Functionality of Interfaces
Microstructure and electronic properties of specific interfaces;
Interface effect on electron/phonon transport;
Microscopic and atomistic modeling of interfaces;
Design high performance materials based on understanding of the effects of size and interface on transport behavior of nanocomposites
Research:
Energy filtering effect
Today’s ICE-based vehicles: < 20% of fuel energy is used for propulsion > 60% of gasoline energy (waste heat) is not utilized
GEN I
GEN II
Typical Energy Path in Gasoline Fueled Internal Combustion Engine Vehicles
GEN III
Co
mb
ust
ion
3 0 % E n g i n e
V e h i c l e O p e r a t i o n
100
%
4 0 % E x h a u s t
G a s
3 0 % C o o l a n t
5 % F r i c t i o n &
R a d i a t e d
2 5 %M o b i l i t y &
A c c e s s o r i e s
Ga
solin
eG
aso
line
Ga
solin
eG
aso
line
Gas
oli
ne
Gas
oli
ne
N o t e : C h a r t s i n t h i s p r e s e n t a t i o n a r e d r a w n f r o m m u l t i p l e s o u r c e sa n d m a y h a v e s l i g h t l y d i f f e r e n t n u m b e r s b e c a u s e o f d i f f e r e n t v e h i c l e s & a s s u m p t i o n s . C o n s i d e rt h e m g e n e r a l e s t i m a t e s , n o t p r e c i s ea n a l y s i s .
Reduce onboard AC without sacrifice passenger comfort level Improve fuel economy and CO2 emission DOE award in place to start in 2009
“If all passenger vehicles had ventilated seats, we estimate that there could be a 7.5 % reduction in national air-conditioning fuel use. That translates to a savings of 522 million gallons of fuel a year,"
John Rugh, project leader for NREL's Vehicle Ancillary Loads Reduction Project.
Distributed Cooling for High Efficiency HVAC System
Case 08
TE ExhaustGenerator
Maximum module compression compliance Quick disconnects for fluid flow Quick disconnect exhaust connections Pitched to drain condensate Pitch designed for boil off Sealed electronics
Located where current muffler is placed; new muffler will be located behind the axle perpendicular to vehicle axis Axially compliant for thermal expansion
mismatch
Interior View(module mounting)
TE ExhaustGenerator
Exhaust Generator GEN III Design
FFL and Electronegativity-based Selection Rule
FFL: Theoretical predictions agree well with experimental data.
Ca Ba La Ce Yb
Exptl
FFL0.20 0.44 0.23 0.10 0.19
Point : What controls the filling fraction limit ?
Competition between the filled phase and possible secondary phases determines the FFL.
x: Electronegativity of atom.
Shi, Zhang*et al, Phys. Rev. Lett. (2005).Shi, Zhang*et al, Phys. Rev. B. (2007).Shi, Zhang*et al, Acta Mater. (2008).
A stable filled CoSb3 has to satisfy an electronegativity-based selection rule:
The Electronegativity-based Selection Rule
The x-based selection rule(x =xSb - xI
>0.80): Most of atoms form no stable filled phase ; RE and AE atoms do form stable filled
phases; AM-filled CoSb3 - novel filled phases ?
Novel filled CoSb3 ?
29
Alkali-metal-filled skutterudites: NayCo4Sb12 and KyCo4Sb12
Na and K has a maximum filling fraction (up to 65%) reported. NayCo4Sb12 shows the highest power factor and ZTs among all single
filled SKTs.
ZT
NaNa0.430.43CoCo44SbSb1212
(n-type)(n-type)
AM-filled CoSb3: 2007 Goldsmid Award (Dr. Pei YZ); Pei, Chen, Zhang, APL (2009,2007); Mei, Zhang, Chen, PRB (2007).
异种填充原子选择规则的指导意义:
Filler atom
Rattling0 (cm-1)
稀土( RE )
La 68
Ce 55
Eu 59
Yb 43
碱土( RE )
Ba 94
Sr 91
碱金属( AM )
Na 113
K 142
Optimal Combinations of multiple fillersOptimal Combinations of multiple
fillers :“Using fillers with largely different
rattling frequencies to realize wide-spectrum phonon scattering, especially for the low-frequency phonons ”
Bad combinations : REs ( Mischmetal ) AEs ( Ba + Sr ) Good combinations : Dual : Ba +Yb , Ba + Ce , Yb + Na ,… Triple : Yb + Ba + Na , …
热电
性能
优值
ZT
Na0.43Co4Sb12
(n-type)
Ba0.08Yb0.09Co4Sb12
(n-type)
ZTs of the Ba-Yb dual-filling CoSb3
Yang, Zhang, Chen et al, Appl. Phys. Lett. 91, (2007)Shi, Yang, Chen, Zhang, Uher* et al, Appl. Phys. Lett. 92, (2008)US patent - with GM, 2008 , #61036715
Ba-Yb dual-filled
CoSb3 reaches
ZT~1.36@850K, Best
among the CoSb3-
based bulk materials !(2008)A series of dual-filled CoSb3 (~ 1.4@850K)
could be obtained easily.
• Calculated resonant phonon frequencies are experimentally validated
5
Yb Eu Ba
La
Rattling Frequency: Calculations vs Inelastic Neutron Scattering Experiment
多填充方钴矿的性能优化
X. Shi, Jiong Yang, W. Zhang, Jihui Yang et al., to be submitted
0.0 0.1 0.2 0.3 0.4 0.5
Total Filling Fraction
AxByCzCo4Sb12
Range of optimal carrier density
Carrier scattering mechanisms in TE materials
Lattice scattering Intravalley: Acoustic – deformation potential Acoustic – piezoelectric Optic – polar Optic – nonpolar Intervalley: Acoustic and optic phonon
Defect scattering: impurity – neutral
impurity – ionized large impurity – boundaries, precipitates,…
Carrier – carrier scattering: …
1. Only a few of them can be dealt with from the bottom of theory;2. The same argument also applies to the study of thermal transport of TE
materials (phonon transport problem).
30
3
2 2
4(( ( ))) t
dot
fe
kE ke v k
电热输运理论研究
'',
1( , '(1 cos )[ ( , ', ) ...], )
( , )defect
kkk
e ph P k kP k kk
Computational Thermoelecrics
Rational Search for novel thermoelectric compounds:
Ab initio understanding of the functionality of the key structural unit;
Exact e-ph scattering from ab initio for relatively quantitative prediction of transport properties
Green-Kubo formula
1 1,
1 1
2
N N
i i ij ij ii j j i
E r FV
J(t)
2 0
1( ) (0) d
B
t tVk T
κ J J
The G-K formula for the thermal conductivity is:
The heat current can be expressed as:
Long running time; Average over results for several different MD runs.
Thermal conductivity from equilibrium MD simulations
i
j
vi
convectionSingle particle
Heat current correlation function
SiC-based nanocomposite
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