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

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1 What to expect from exploratory synthesis: intermetallics, chalcogenides and thermoelectrics April , Northwestern University Mercouri G. Kanatzidis Department of Chemistry, Northwestern University and Argonne National Laboratory

2 Outline Why exploratory synthesis Chalcogenides Thermoelectrics Unusual structures and homologies Ion exchangers Intermetallics Conclusions

3 The periodic table according to some Alkali metals hard metals Au C Si Bi H Noble Rare metals Metals for weapons

4 Why Do Exploratory Synthesis? New Materials Advance the cutting edge of what it possible New compositions, new structures Unusual properties New synthesis methods (synthetic toolbox ) Learn more about structure/property relationships Discover 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

5 First: define Design Design Structure/composition Design Function Design 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

6 Many Levels of Design Highest Level: Target a property you want, then synthesize a material which has the property High Level: Envision a structure, then synthesize it Moderate: Adjust (or optimize) a property systematically by making small changes in a known material Band gap engineering is an example, Cd 1-x Hg x Te, Al 1-x Ga x As. Very successful Achieving isomorphous substitutions (making analogs) K 2 SO 4 > Ba 2 SnTe 4 K 2 MnSnS 4 > K 2 ZnSnS 4 > K 2 CdSnS 4 > K 2 HgSnS 4 > ZrSiS > NbSiAs Zr 4+ Si 2- S 2- Nb 5+ Si 2- As 3- Irrational synthesis

7 A solid state chemist s view of organic chemistry O At 800 o C CO 2 CO H 2 O 2 C C 2 H 2 HCOOH H 2 CO CH 4 H 2 O H

8 An organic chemist s view of solid state chemistry: Turn down the heat use solvents Lower temperatures stabilize greater numbers of compounds Need solvents: The molten salt method parallels solution based synthesis Different fluxes can be devised for different materials. These fluxes can be reactive or non reactive.

Polychalcogenide Flux Molten chalcogenide salts (A 2 Q + Q x A 2 Q x ) as Reagents and Solvents to synthesize new compounds ADVANTAGES Low temperatures (250 o C < T < 750 o C) Can produce compounds

9 Polychalcogenide Flux Molten chalcogenide salts (A 2 Q + Q x A 2 Q x ) as Reagents and Solvents to synthesize new compounds ADVANTAGES Low temperatures (250 o C < T < 750 o C) Can produce compounds not accessible by other methods Kinetic products / Thermodynamic products Conducive to large crystal growth Ability to produce in pure form more complicated compounds such as ternary: A/Bi/Q or quaternary: A/M/Bi/Q) Starting materials + Flux M. G. Kanatzidis and A. Sutorik Progress in Inorganic Chemistry 1995, 43, Molten crystals

10 Reactivity of molten K 2 S x When T>600 o C: CuS, Cu 2 S, KCuS In K 2 S 5 and 350<T<600 o C: KCu 4 S 3, KCu 7 S 4 In K 2 S 5 and 180<T<350 o C: α-kcus 4, β- KCuS 4, KCuS 6, KCu 4 S 4, KCu 8 S 6

11 Investigating the A/Bi/Q system A 2 Q + PbQ + M 2 Q 3 > (A 2 Q) n (PbQ) m (M 2 Q 3 ) p Map generates target compounds Cubic materials A m B n M m Q 2m+n Phases shown are promising new TE materials A 2 Q Rb 0.5 Bi 1.83 Te 3 A=Ag, K, Rb, Cs M=Sb, Bi Q=Se, Te PbQ APb 2 Bi 3 Te 7 A 1+x Pb 4-2x Bi 7+x Se 15 Pb 6 Bi 2 Se 9 Pb 5 Bi 6 Se 14 Pb 5 Bi 12 Se 23 β-k 2 Bi 8 Se 13 CsBi 4 Te 6 Bi 2 Q 3

12 Compounds discovered K 2 Bi 8 Se 13, KPbBi 9 Se 13, KPb 4 Sb 7 Se 15 Cs 1-x Pb 5-x Bi 10+x Se 21 CsPbBi 3 Te 6, CsPb 2 Bi 3 Te 7, RbPbBi 3 Te 6, RbPb 2 Bi 3 Te 7, RbPb 3 Bi 3 Te 8, KPbBiSe 3, K 2 PbBi 2 Se 5 K 2 Pb 3 Bi 2 Te 7, KPb 4 SbTe 6

CsPb 7 Bi 9 Se 21 800 Cs 0.6 Pb 6.6 Bi 9.

13 CsPb 7 Bi 9 Se Cs 0.6 Pb 6.6 Bi 9.4 Se 21 Conductivity (S/cm) Temperature (K) 0 ZT 300 K =0.6 ZT=(σs*S/κ)T Sample undoped. Anticipated high ZT by doping. Thermopower (µv/k) Temperature (K) DY Chung MG Kanatzidis

KM 4 Bi 7 Se 15 (M = Pb, Sn) KPb 4 Bi 7 Se 15 (undoped) 600 0 550 500-50 Conductivity (S/cm) 450 400 350 300-100 -150 Thermopower (μv/k) 250 200-200 0 50 100 150 200 250 300 350 Temperature (K) 1.6 1.

14 KM 4 Bi 7 Se 15 (M = Pb, Sn) KPb 4 Bi 7 Se 15 (undoped) Conductivity (S/cm) Thermopower (μv/k) Temperature (K) κ (W/m-K) 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, Temperature (K)

15 Chemistry : A m [M 1+l Se 2+l ] 2m [M 2l+n Se 2+3l+n ] l n 1, M2+nSe5+n 2, M4+nSe8+n 0 M2Se5 M4Se8 l m 1, [M2Se3] 2m 2, [M3Se4] 2m 1 M3Se6 M5Se9 1 2 M4Se7 M6Se10 M4Se6 M6Se8 3 M5Se8 M7Se M6Se9 M8Se12 M8Se12 M12Se16 5 M7Se10 M9Se13 6 M8Se11 M10Se14 M11Se14 (n=9) M14Se18 (n=10)

16 Design of Structure using phase homologies A m [ M 1+l Se 2+l ] 2m [ M 2l+n Se 2+3l+n ] A. Mrotzek, D.-Y. Chung, T. Hogan, M.G. Kanatzidis J. Mater. Chem. 2000, 10, A. Mrotzek, M.G. Kanatzidis, J. Solid State Chem. 2002, 167, 299. A. Mrotzek, M.G. Kanatzidis, Acc. Chem. Res. 2003, 36, 111.

17 Selection criteria for TE candidate materials Narrow band-gap semiconductors Heavy elements High mobility, low thermal conductivity Large unit cell, complex structure low thermal conductivity Highly anisotropic or highly symmetric Complex compositions low thermal conductivity, electronic structure

18 CsBi 4 Te 6 Cs Bi Te z y x Bi-Bi bond

19 0.05 % SbI 3 -doped CsBi 4 Te 6 Conductivity (S/cm) Thermopower (µv/k) 1.0 At 225 K : σ 1733 S/cm, S 177 µv/k, κ 1.48 W/m. K CsBi 4 Te 6 doped Temperature (K) p-bi 2 Te 3 Marlow ZT κ (W/m. K) Temperature (K) Temperature (K) 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

20 AgPb m SbTe 2+m (LAST-m) NaPb m SbTe 2+m (SALT-m) Pb Te Sb Ag 268 Unit cell volume (Å) Single crystal data Vegard's law Powder data m value (1) (a) Rodot, H. Compt. Rend. 1959, 249, (2) (a) Rosi, F. D.; Hockings, E. S.; Lindenblad, N. E. Adv. Energy Convers. 1961, 1, 151.

21 Properties of Ag 1-x Pb 18 SbTe Lattice thermal conductivity σ (S/cm) Temperature, K Lattice Thermal Conductivity (W/mK) S (μv/k) PbTe LAST W/mK (Harman PbTe/PbSe superlattice) Temperature (K)

22 Ag 1-x Pb 18 SbTe Ag 0.86 Pb 18 SbTe ZT Temperature, K Hsu KF, Loo S, Guo F, Chen W, Dyck JS, Uher C, Hogan T, Polychroniadis EK, Kanatzidis MG Science, 2004, 303, 818

23 Coherently embedded nanocrystals Polychroniadis, Frangis, 2004 LAST-18 κlatt=1.2 W/m-K at 300 K PbTe κlatt=2.2 W/m-K at 300 K

24 Driving force for segregation Ag + /Sb 3+ pair: stable Pb Te Pb Te Pb Te Pb Te Pb Pb Te Sb Pb Te Pb Te Pb Te Pb Dissociated state..unstable Te Ag Te Pb Te Pb Te Pb Te Pb Te Pb Te Pb Pb Te Pb Te Pb Te Pb Te Pb Te Pb Te Pb Te Pb Pb Te Pb Pb Te Sb Te Pb Te Pb Associated state..stable Te Ag Te Pb Te Pb Te Pb Te Pb Te Pb Te Pb Pb Te Pb Te Pb Te

NaPb 20 SbTe 22 (SALT-20) (A) Lattice Thermal conductivity (W/mK) 50 nm 2 (B) 1.5 Pb Sn Te 0.9 0.

25 NaPb 20 SbTe 22 (SALT-20) (A) Lattice Thermal conductivity (W/mK) 50 nm 2 (B) 1.5 Pb Sn Te PbTe Se Na Pb SbTe 1-x Temperature, K

26 Best ZT Materials 2 LAST 1.5 Na 0.95 Pb 20 SbTe 22 LASTT TAGS Tl 9 BiTe 6 1 β-k 2 Bi 8 Se 13 PbTe Ce 0. 9 Fe 3 CoSb 12 SiGe CsBi 4 Te Bi 2 Te Temperature (K)

27 Open framework materials from flux chemistry Zn + Sn + xs K 2 S o C K 6 Zn 4 Sn 5 S 17 + K 2 S x flux

28 K 5 Sn[Sn 4 Zn 4 S 17 ] from molten K 2 S 6 K3 K2 K1 K ions loose and exchangeable 3 different type of cages

29 Ion-exchange experiments of K 6 Sn[Zn 4 Sn 4 S 17 ] with Hg 2+, Pb 2+, Cd 2+, Ag + K 6 Sn[Zn 4 Sn 4 S 17 ] + M(NO 3 ) 2 (1:1, 1:2, 1:2.5, 2:1, 4.5:1) mg (M= Hg, Pb, Cd) 30 min stirring, RT H 2 O, 16 ml Reduces: Hg 2+ conc. from 400 ppm to <3 ppb Pb 2+ conc. from 400 ppm to <50 ppb Cd 2+ conc. from 400 ppm to <0.5 ppm K 6 Sn[Zn 4 Sn 4 S 17 ] (H 2 O) K 6 Sn[Zn 4 Sn 4 S 17 ] Hg(NO 3 ) 2 (H 2 O)

30 Mercury removal: K 6 Sn[Zn 4 Sn 4 S 17 ] vs. functionalized mesoporous silicates Initial concentration (ppm) of Hg Material Final concentration (ppm) of Hg K d (ml/g) 6.2 FMMS PMPS S FMMS K 6 Zn 4 Sn 5 S x10 8 FMMS: functionalized monolayers on mesoporous silica Higher affinity of K 6 Sn[Zn 4 Sn 4 S 17 ] for Hg than functionalized silicates

31 Sorting cations: CsK(NH 4 ) 2.71 Rb 1.29 Sn[Zn 4 Sn 4 S 17 ] Pore selectivity: Largest cavity (K3): Cs 100% Small cavity(k1): K 100% Second large cavity (K2): NH %, Rb 32.25% Cs + Manos, Kanatzidis

32 K 2x [Sn 3-x Mn x S 6 ] (KMS-1)

33 Sr uptake by KMS-1

Exploration of Intermetallics Using Liquid Al and Ga

ZrNiSn YbAl 3 YbCu 2 Si 2 "The great field of

one another have been largly neglected by chemists

.. " "There is chemistry in intermetallics" -- John

34 Exploration of Intermetallics Using Liquid Al and Ga Some important intermetallics Mg-Si-Al Nb 3 Sn MgB 2 ZrNiSn YbAl 3 YbCu 2 Si 2 "The great field of chemistry comprising the compounds of metals with one another have been largly neglected by chemists in the past... " "There is chemistry in intermetallics" -- John Corbett Traditional solid state synthesis--combine stoichiometric ratios and heat to high temperature

35 Some Statistics Binary Systems: A x B y ~ 20,000 compounds known; about 80% of all possible combinations Ternary Systems: A x B y C z Only ~ 5% of 100,000 possible combinations have been discovered Quaternary Systems: A x B y C z Q m Only few representatives are known DiSalvo, F. J., Solid State Chemistry, Solid State Commun., 1997, 102,

36 Synthesis in liquid Al Al-Si phase diagram Up 30% Si at 900 o C. A + B Al C

37 Quaternary intermetallics grown in liquid metals Al RE + M + Si RE x M y Si z Sm 2 NiAl 4 Si 7, RE 4 Fe 2 Al 7 Si 8, RE 8 Ru 12 Al 49 Si μm MnSi 2 Yb 2 NiSi YbNiSi RuIn 3 M. G. Kanatzidis, R. Poettgen, W. Jeitschko, Angew Chemie, 2005, 117, 7156 YbCoGe 2

38 The Homologous RE[AuAl 2 ] n Al 2 (Au x Si 1-x ) 2 series Possible next homologue: REAu 5 Al 10 Si: RE[AuAl 2 ] 4 Al 2 (Au x Si 1-x ) 2 I4/mmm 4 x 34 Å AuAl 2 REAu 2 Al 4 Si REAu 1-x Al 2 Si 1+x BaAl 4 type EuAu 3-x Al 6 Si 1+x REAu 4-x Al 8 Si 1+x

39 M 3 Au 7 Al 26 T Serendipitous discovery: TiO 2 cement in crucible reacted with Yb/Au/Al reaction mixture (YbAu 3 Al 7 ) Gold analogs form only with divalent or mixed-valent M ions: Ca, Sr, Eu, Yb. M = Yb, Eu, Ca, Sr Empty Hg 8 cube Au - Stuffed Al 8 cube Ba BaHg 11 Pm-3m, a = 9.60¹ Yb 3 Au 7 Al 26 Ti Pm-3m, a = (6)¹ 1 Zarechnyuk, et al. Inorg. Mater. 1967, 3, 153

40 Chemistry in liquid Ga: RE 5 Co 4 Si 14 Tm(2) Tm Tm(3) Co Si Co(2) Co(1) a c I 4/mmm Salvador, Kanatzidis P 2 1 /c

41 Resistance to Oxidation Melting point>1200 o C 110 Weight % Tm Co Si Tm(2) Tm(3) Co(2) After 900 o C for 12h 85 Co(1) a 1000 Temperature ( C) c (100) (101)

Yb 7 Co 4 InGe 12 - crystal structure X-Ray Absorption Near Edge Spectroscopy (XANES) Normalized Absorption [a. u.] 2 1.5 1 0.

Energy (ev) 60 5 10 15 20 25 T(K) Poor metallic behavior Negative magneto-resistance: suppression of spinscattering of

42 Yb 7 Co 4 InGe 12 - crystal structure X-Ray Absorption Near Edge Spectroscopy (XANES) Normalized Absorption [a. u.] Yb 300K Yb 15K 8940 ev ev ρ (µω cm) T 1T 5T Energy (ev) T(K) Poor metallic behavior Negative magneto-resistance: suppression of spinscattering of conduction & f-electrons in a high field frequently seen in Kondo systems, heavy fermion systems M. Chondroudi, U. Welp, M. Balasubramanian

43 exploratory synthesis leads to synthesis by design TNT Exploratory synthesis 5 th generation dendrimer Reactivity principles And patterns Taxol Design

44 Conclusions Exploratory synthesis is the foundation of synthetic chemistry Synthesis methodologies are critical to materials discovery Apparently useless materials today may be the hot materials of tomorrow.. LaO(FeAs) (LaO 1-x F x )(FeAs) superconductor up to 50 K! Some apparently useless materials in the 60s and 70s: E.g. LnFe 4 Sb 12 (skutterudites), ZnNiSn (Heussler alloys), CeCu 2 Si 2, MgB 2 La 2-x Ba x CuO 4, (NH 4 ) 2 MoS 4. 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

45 Collaborators Tim Hogan, MSU S. D. (Bhanu) Mahanti, Dept. of Physics, MSU Ctirad Uher, U of Michigan Simon Billinge, Physics, MSU Eldon Case, MSU Harold Schock, MSU Bruce Cook, Iowa State Ulrich Welp, Argonne NL Art Freeman, Northwestern David Seidman, Northwestern

Anisotropy in Thermoelectric Properties of CsBi 4 Te 6

Mat. Res. Soc. Symp. Proc. Vol. 793 24 Materials Research Society S6.1.1 Anisotropy in Thermoelectric Properties of CsBi 4 Te 6 Duck-Young Chung 1, S. D. Mahanti 2, Wei Chen 3, Citrad Uher 3, Mercouri