Mercouri G. KanatzidisDepartment of Chemistry, Northwestern University and Argonne National Laboratory

What to expect from exploratory synthesis: intermetallics, chalcogenides and thermoelectrics

April 15 2008, Northwestern University

Outline

Why exploratory synthesisChalcogenides

ThermoelectricsUnusual structures and homologiesIon exchangers

IntermetallicsConclusions

The periodic table according to some…

CH

Bi

Alka

li m

etal

s

hard metals

Nob

le

Si

Rare metalsMetals for weapons

Au

Why Do Exploratory Synthesis?New Materials

Advance the cutting edge of what it possibleNew compositions, new structuresUnusual propertiesNew synthesis methods (synthetic toolbox…)Learn more about structure/property relationshipsDiscover the unpredictable

The elucidation of a structure can help us think logically as to what experimentation can be done with it. Predicting the outcome of a solid state reaction is difficult, if not impossible, which makes exploratory synthesis an invaluable tool.

Expand the shelf…Ultimate goal: design of materials

First: define “Design”

Design Structure/compositionDesign FunctionDesign Synthesis

“Design” is a word rich with ambiguity and highly dependent on context

The challenge of Designing New Materials requires us to span the distance from “Observe and Analyze” to “Predict and Control”

Many Levels of Design

Highest Level: Target a property you want, then synthesize a material which has the propertyHigh Level: Envision a structure, then synthesize itModerate: Adjust (or optimize) a property systematically by making small changes in a known material

Band gap engineering is an example, Cd1-xHgxTe, Al1-xGaxAs. Very successfulAchieving isomorphous substitutions (making analogs)

K2SO4 –––> Ba2SnTe4

K2MnSnS4––> K2ZnSnS4––> K2CdSnS4––> K2HgSnS4––> ZrSiS –––––> NbSiAs

Zr4+ Si2- S2- Nb5+ Si2- As3- Irrational synthesis…

A solid state chemist’s view of organic chemistry

C

O

H

CO

CO2

H2O

H2O2

CH4

H2CO●

HCOOH●

At 800 oC

C2H2

Lower temperatures stabilize greater numbers of compoundsNeed solvents: The molten salt method parallels solution based synthesisDifferent fluxes can be devised for different materials. These fluxes can be reactive or non reactive.

An organic chemist’s view of solid state chemistry: Turn down the heat…use solvents

Polychalcogenide Flux

Molten chalcogenide salts (A2Q + Qx→ A2Qx) as Reagents and Solvents to synthesize new compounds

ADVANTAGESLow temperatures (250 oC < T < 750 oC)Can produce compounds not accessible by other methods□ Kinetic products / Thermodynamic products

Conducive to large crystal growthAbility to produce in pure form more complicated compounds such as ternary: A/Bi/Q or quaternary: A/M/Bi/Q)

Starting materials+ Flux

Molten… crystals

M. G. Kanatzidis and A. Sutorik Progress in Inorganic Chemistry1995, 43, 151-265.

Reactivity of molten K2Sx

When T>600 oC: CuS, Cu2S, KCuSIn K2S5 and 350<T<600 oC : KCu4S3, KCu7S4

In K2S5 and 180<T<350 oC : α-KCuS4, β-KCuS4, KCuS6, KCu4S4 , KCu8S6

A2Q + PbQ + M2Q3 –––––> (A2Q)n(PbQ)m(M2Q3)p

Investigating the A/Bi/Q system

A2Q

PbQBi2Q3

A=Ag, K, Rb, CsM=Sb, BiQ=Se, Te

β-K2Bi8Se13

Rb0.5Bi1.83Te3

Pb5Bi6Se14

A1+xPb4-2xBi7+xSe15

APb2Bi3Te7

Pb6Bi2Se9 Pb5Bi12Se23

Map generates target compounds

CsBi4Te6

Phases shownare promising new TEmaterials

Cubic materialsAmBnMmQ2m+n

Compounds discovered

K2Bi8Se13, KPbBi9Se13, KPb4Sb7Se15

Cs1-xPb5-xBi10+xSe21

CsPbBi3Te6, CsPb2Bi3Te7, RbPbBi3Te6, RbPb2Bi3Te7, RbPb3Bi3Te8,KPbBiSe3, K2PbBi2Se5

K2Pb3Bi2Te7, KPb4SbTe6

CsPb7Bi9Se21

Sample undoped. Anticipated high ZT by doping.

ZT300 K=0.6

-200

-150

-100

-50

0

0 50 100 150 200 250 300

Ther

mop

ower

(µV

/K)

Temperature (K)

600

650

700

750

800

0 50 100 150 200 250 300

Con

duct

ivity

(S/c

m)

Temperature (K)

Cs0.6Pb6.6Bi9.4Se21

ZT=(σs*S/κ)T

DY Chung MG Kanatzidis

KM4Bi7Se15 (M = Pb, Sn)

200

250

300

350

400

450

500

550

600

-200

-150

-100

-50

0

0 50 100 150 200 250 300 350

Con

duct

ivity

(S/c

m) Therm

opower ( μV/K)

Temperature (K)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 50 100 150 200 250 300

κ (W

/m-K

)

Temperature (K)

KPb4Bi7Se15 (undoped)

K.-S. Choi, D.-Y. Chung, A. Mrotzek, P. Brazis,C. R. Kannewurf, C. Uher, W. Chen, T. Hogan, M.G. Kanatzidis Chem. Mater. 2001, 13, 756.

Chemistry : Am[M1+l Se2+l]2m[M2l+nSe2+3l+n]

lm 1, [M2Se3]2m 2, [M3Se4]2m

1

2

M6Se8

M8Se12

M4Se6

M12Se16

ln 1, M2+nSe5+n 2, M4+nSe8+n

1

2

3

M4Se8

M6Se10

M7Se11

M8Se12

M9Se13

M10Se14

M14Se18 (n=10)

0

M11Se14 (n=9)

M8Se11

M7Se10

M6Se9

M5Se8

M4Se7

M3Se6

M2Se5

M5Se9

4

5

6

Design of Structure using phase homologies

Am [ M1+l Se2+l ]2m [ M2l+nSe2+3l+n ]

A. Mrotzek, D.-Y. Chung, T. Hogan, M.G. Kanatzidis J. Mater. Chem. 2000, 10, 1667.A. Mrotzek, M.G. Kanatzidis, J. Solid State Chem. 2002, 167, 299.A. Mrotzek, M.G. Kanatzidis, Acc. Chem. Res. 2003, 36, 111.

Selection criteria for TE candidate materials

Narrow band-gap semiconductorsHeavy elements

High mobility, low thermal conductivityLarge unit cell, complex structure

low thermal conductivity Highly anisotropic or highly symmetric…Complex compositions

low thermal conductivity, electronic structure

CsBi4Te6

xy

z

Bi-Bi bond

Cs

Bi

Te

D.-Y. Chung, T. Hogan, M. Rocci-Lane, P. Brazis, J. Ireland, C. Kannewurf, M. Bastea, C. Uher, and M. Kanatzidis, Science, 2000, 287, 1024

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 50 100 150 200 250 300

κ (W

/m. K)

Temperature (K)

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

0 50 100 150 200 250 300 350

CsBi4Te

6 doped

p-Bi2Te

3 Marlow

ZT

Temperature (K)

0

2000

4000

6000

8000

10000

0

50

100

150

200

0 50 100 150 200 250 300

Con

duct

ivity

(S/c

m) Therm

opower (µV

/K)

Temperature (K)

At 225 K :σ 1733 S/cm, S 177 µV/K, κ 1.48 W/m.K

0.05 % SbI3-doped CsBi4Te6

AgPbmSbTe2+m (LAST-m) NaPbmSbTe2+m (SALT-m)

6 8 10 12 14 16 18

263

264

265

266

267

268

Uni

t cel

l vol

ume

(Å)

Vegard's law

m value

Powder data

Single crystal data

(1) (a) Rodot, H. Compt. Rend. 1959, 249, 1872-4. (2) (a) Rosi, F. D.; Hockings, E. S.; Lindenblad, N. E. Adv. Energy Convers. 1961, 1, 151.

AgSbTe

Pb

AgSbTe

Pb

Properties of Ag1-xPb18SbTe20

0

500

1000

1500

2000

-400

-350

-300

-250

-200

-150

-100

300 350 400 450 500 550 600 650 700

σ (S

/cm

) S (μV

/K)

Temperature, K

0.35 W/mK (Harman PbTe/PbSe superlattice)0

0.5

1

1.5

2

2.5

300 400 500 600 700 800

Latti

ce T

herm

al C

ondu

ctiv

ity (W

/mK

)

Temperature (K)

PbTe

LAST-18

Lattice thermal conductivity

Ag1-xPb18SbTe20

Hsu KF, Loo S, Guo F, Chen W, Dyck JS, Uher C, Hogan T, Polychroniadis EK, Kanatzidis MG Science, 2004, 303, 818

0.00

0.50

1.00

1.50

2.00

300 350 400 450 500 550 600 650 700

Ag0.86

Pb18

SbTe20

ZT

Temperature, K

Coherently embedded nanocrystals

Polychroniadis, Frangis, 2004LAST-18 κlatt=1.2 W/m-K at 300 KPbTe κlatt=2.2 W/m-K at 300 K

Driving force for segregation Ag+/Sb3+ pair: stable

Pb Te Pb Te Pb Te Pb

Te Pb Pb Te Pb

Pb Te Sb Te Pb Te Pb

Te Ag Te Pb Te Pb Te

Pb

Pb

Te

Te

Pb

Pb

Te

Te

Pb

Pb

Te

Te

Pb

Pb Te Pb Te Pb Te Pb

Te Pb Pb Te Sb

Pb Te Pb Te Pb Te Pb

Te Ag Te Pb Te Pb Te

Pb

Pb

Te

Te

Pb

Pb

Te

Te

Pb

Pb

Te

Te

Pb

Dissociated state..unstable

Associated state..stable

NaPb20SbTe22 (SALT-20)

0

0.5

1

1.5

2

300 350 400 450 500 550 600 650 700

Latti

ce T

herm

al c

ondu

ctiv

ity (W

/mK

)

Temperature, K

PbTe0.9

Se0.1

Pb0.9

Sn0.1

Te

Na1-x

Pb20

SbTe22

(B)

(A)

50 nm

Best ZT Materials

0

0.5

1

1.5

2

0 200 400 600 800 1000 1200 1400

Temperature (K)

CsBi4Te

6

Bi2Te

3

Tl9BiTe

6

LAST

LASTTNa

0.95Pb

20SbTe

22

TAGS

Ce0.9

Fe3CoSb

12PbTe SiGeβ -K2Bi

8Se

13

Open framework materials from flux chemistry

Zn + Sn + xs K2S6 K6Zn4Sn5S17 + K2Sx400 oC

flux

K5Sn[Sn4Zn4S17] from molten K2S6

K ions loose and exchangeable 3 different type of cages

K1

K2

K3

K6Sn[Zn4Sn4S17] + M(NO3)2 (1:1, 1:2, 1:2.5, 2:1, 4.5:1)

30-40 mg

30 min stirring, RT

H2O, 16 ml

K6Sn[Zn4Sn4S17] (H2O)

(M= Hg, Pb, Cd)

K6Sn[Zn4Sn4S17]+ 2.5 Hg(NO3)2 (H2O)

Reduces:Hg2+ conc. from 400 ppm to <3 ppbPb2+ conc. from 400 ppm to <50 ppbCd2+ conc. from 400 ppm to <0.5 ppm

Ion-exchange experiments of K6Sn[Zn4Sn4S17] with Hg2+, Pb2+, Cd2+, Ag+

Mercury removal: K6Sn[Zn4Sn4S17] vs. functionalized mesoporous silicates

1080.001FMMS10

2.8x1080.001K6Zn4Sn5S17542.31

42480.23S1210.76

38124000.00016PMPS33401410.0007FMMS6.2

Kd (ml/g)Finalconcentration (ppm) of Hg

MaterialInitial concentration (ppm) of Hg

Higher affinity of K6Sn[Zn4Sn4S17] for Hg than functionalized silicatesFMMS: functionalized monolayers on mesoporous silica

Sorting cations: CsK(NH4)2.71Rb1.29Sn[Zn4Sn4S17]

Pore selectivity:

Largest cavity (K3): Cs 100%

Small cavity(K1): K 100%

Second large cavity (K2): NH467.75%, Rb 32.25%

Cs+

Manos, Kanatzidis

K2x[Sn3-xMnxS6] (KMS-1)

Sr uptake by KMS-1

Exploration of Intermetallics Using Liquid Al and Ga

"The great field of chemistry comprising the compoundsof metals with one another have been largly neglected by chemists in the past ... "

"There is chemistry in intermetallics"

-- John Corbett

Some important intermetallics

Mg-Si-AlNb3SnMgB2ZrNiSnYbAl3YbCu2Si2

Traditional solid state synthesis--combine stoichiometric ratios and heat to high temperature

Some Statistics …Binary Systems: AxBy

~ 20,000 compounds known; about 80% of all possible combinations

Ternary Systems: AxByCzOnly ~ 5% of 100,000 possible combinations have been discovered

Quaternary Systems: AxByCzQmOnly few representatives are known

DiSalvo, F. J., “Solid State Chemistry” , Solid State Commun., 1997, 102, 79-85.

Synthesis in liquid Al

Up 30%Si at 900 oC.

AlAl--Si phase diagramSi phase diagram

A + B CAl

Quaternary intermetallics grown in liquid metals

RE + M + Si RExMySizSm2NiAl4Si7, RE4Fe2Al7Si8, RE8Ru12Al49Si21

Al

M. G. Kanatzidis, R. Poettgen, W. Jeitschko, Angew Chemie, 2005, 117, 7156YbCoGe2

Yb2NiSiYbNiSi

RuIn3

500 μm

MnSi2

The HomologousRE[AuAl2]nAl2(AuxSi1-x)2 series

REAu4-xAl8Si1+xEuAu3-xAl6Si1+x

REAu2Al4SiREAu1-xAl2Si1+x

BaAl4 type

AuAl2

Possible next homologue:REAu5Al10Si: RE[AuAl2]4Al2(AuxSi1-x)2I4/mmm 4 x 34 Å

Serendipitous discovery: TiO2 cement in crucible reacted with Yb/Au/Al reaction mixture (YbAu3Al7)

Gold analogs form only with divalent or mixed-valent M ions: Ca, Sr, Eu, Yb.

M3Au7Al26T

BaHg11

Pm-3m, a = 9.60¹

Ba

Empty Hg8 cube Au - Stuffed

Al8 cube

Yb3Au7Al26Ti

Pm-3m, a = 8.6509(6)¹

M = Yb, Eu, Ca, Sr

1Zarechnyuk, et al. Inorg. Mater. 1967, 3, 153

Chemistry in liquid Ga: RE5Co4Si14

a

c

Co(2)

Tm(3)

Tm(2)

Co(1)

Tm

Co

Si

P 21/cI 4/mmm Salvador, Kanatzidis

Resistance to Oxidation

80

85

90

95

100

105

110

0 200 400 600 800 1000

Wei

ght %

Temperature (° C)a

c

Co(2)

Tm(3)

Tm(2)

Co(1)

Tm

Co

Si

(100) (101)

After 900 oC for 12h

Melting point>1200 oC

Yb7Co4InGe12 - crystal structureX-Ray Absorption Near Edge Spectroscopy (XANES)

60

70

80

90

100

110

120

5 10 15 20 25

0T1T5T

ρ (µΩ

cm

)

T(K)

0

0.5

1

1.5

2

8930 8935 8940 8945 8950 8955 8960 8965

Yb 300KYb 15K

Nor

mal

ized

Abs

orpt

ion

[a. u

.]

Energy (eV)

3+

2+

8948 eV

8940 eV

8948 eV

8940 eV

Poor metallic behavior Negative magneto-resistance: suppression of spin-

scattering of conduction & f-electrons in a high fieldfrequently seen in Kondo systems, heavy fermion

systemsM. Chondroudi, U. Welp, M. Balasubramanian

exploratory synthesis leads to “synthesis by design”

TNT Taxol5th generation dendrimer

Exploratory synthesis Reactivity principlesAnd patterns Design

ConclusionsExploratory synthesis is the foundation of synthetic chemistrySynthesis methodologies are critical to materials discoveryApparently “useless” materials today may be the hot materials of tomorrow..

LaO(FeAs) (LaO1-xFx)(FeAs) superconductor up to 50 K!Some apparently useless materials in the 60s and 70s:

E.g. LnFe4Sb12 (skutterudites), ZnNiSn (Heussler alloys), CeCu2Si2, MgB2La2-xBaxCuO4, (NH4)2MoS4.

If it doesn’t exist, you can’t measure it.Grand challenge: design of specific compounds to obtain specific properties: e.g. superconductors, thermoelectrics, photovoltaics, magnets, ferroelectrics, etc.

“Expect the unexpected or you may not find it…” Heraclitus, 500 BC

CollaboratorsTim Hogan, MSUS. D. (Bhanu) Mahanti, Dept. of Physics, MSUCtirad Uher, U of MichiganSimon Billinge, Physics, MSUEldon Case, MSUHarold Schock, MSUBruce Cook, Iowa StateUlrich Welp, Argonne NLArt Freeman, NorthwesternDavid Seidman, Northwestern