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