Research Activities and Interests
What We Do

 

Kanatzidis Research Group






We are interested in the design, synthesis, synthetic methodology, in- depth characterization, manipulation and potential applications of new substances with novel chemical, physical, or electrical properties. These substances range from discrete molecular compounds, to solid state inorganic materials, to organic polymeric materials. We seek to obtain deeper understanding of synthesis/structure relationships and structure/function relationships.

The topics of current activity include:

Solid State Chemistry of Chalcogenides

New Thermoelectric Materials

Non-oxidic Solids with Open-Framework Structures (nano-science)

Intermetallics from molten Al, Ga and In

Low-dimensional nano-composites between polymers and inorganic phases (nanoscience)

Hyrdothermal synthesis of novel metal chalcogenide compounds.
 
 

  1. Solid State Chemistry of Chalcogenides

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    Perhaps no other area of chemical synthesis more deserves the title "exploratory" than does solid state synthesis. The majority of synthetic chemists have a measure of predictability in that the molecular units they work with remain relatively intact throughout their reactions, and so their goal is mainly to link one molecule to the next or to perform specific changes on molecular functional groups. The solid state synthetic chemist has almost no predictability in his reactions save for the simplest cases of elemental substitution, and even then can still have his predictions frustrated.

    Hope to change this in the future. We work on the development of novel Synthetic Methodologies for the class of metal chalcogenide compounds. This involves the exploration of molten solids and their application as solvents for exploratory synthesis and crystal growth. It also involves the use of stable preformed building blocks that end up in the final structures giving the solid a certain functionality.

    In many ways we approach this chemistry from a solution chemistís outlook rather than a conventional high temperature solid state chemistsís perspective. This allows for useful and profitable insights to be drawn from what is already known in coordination chemistry.

    Although techniques will become more sophisticated, one hundred percent synthetic predictability is not likely to be achieved in any type of chemical synthesis. We will always have the unknown to frustrate, motivate, and inspire us.
     
     
     
     

  2. New Thermoelectric Materials

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    The challenge in any effort to discover new thermoelectric (TE) materials lies in achieving simultaneously high electronic conductivity, high thermoelectric power and low thermal conductivity in the same solid.These properties define the thermoelectric figure of merit ZT = (S2s/k )T; where S is the thermopower, s the electronic conductivity, k the thermal conductivity, and T the temperature. The first three quantities are determined by the details of the electronic structure and scattering of charge carriers (electrons or holes) and thus are not independently controllable parameters. The thermal conductivity has a contribution from lattice vibrations, kl which is called the lattice thermal conductivity . Thus k = ke + kl, where ke is the carrier thermal conductivity.

    Our efforts aim to synthesize bulk materials with higher figures of merit than those attainable with Bi2Te3. Several new ideas and approaches to the design of improved thermoelectric materials have stimulated a resurgence of interest in this old field. The least understood problem is how to increase the thermopower of a material without depressing the electronic conductivity and how to predict precisely which materials will have very large thermopower.

    Although there are many different approaches and avenues taken by different groups around the world, we have our own approach to new thermoelectric materials, which is to explore complex chalcogenide materials using newly developed solid state synthetic techniques for these systems.

    We are not merely interested in new compounds that are substitutions and variations of known structures, but in entirely new structure types. If significantly enhanced TE properties are to be found, new materials must become available. Therefore, novel types of syntheses must be explored which allow for higher ZTs. Since the electrical properties of solids are directly dependent on their crystal structure, we are motivated to look for new materials with new lattice structures.

    Interest in TE materials is not new but the need for new materials is increasing and the next decade will be critical in the development of this field. Taking into account the difficulty if identifying the "right" compound and optimizing to ZT > 1, long term sustainable planning is necessary and close collaboration between chemists, physicists and engineers is key to success. Such collaborative approaches have been the paradigm in which the present effort is based.

    Heavy element chalcogenides

    Environmentally stable Zintl phases

    Collaboration with Tellurex Inc.
     
     
     
     

  3. Non-oxidic Solids with Open-Framework Structures (nano-science)

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    Mesostructured non-oxidic solids

    Microstructured non-oxidic solids
     
     

    Mesoporous materials have attracted considerable attention in the last decade, because of their immense technological potential as catalysts, adsorbents and hosts for large molecules. The mesoporous silicates of the MCM-n family with ordered pore structure, reported by the Mobil group using long chain organic molecules as 'structure directing' agents, have spawned a new era in open framework materials. Porous low band-gap non-oxidic systems, such as chalcogenides are also of great interest because new applications could be foreseen by combining the porous nature with their semiconducting and opto-electronic properties in fields of photocatalysis nanotechnology etc.

    Sulfide selenide and telluride-based and other non-oxidic open-framework materials are intriguing compounds. Apart from the fact that they possess a very diverse and therefore interesting structural chemistry, these materials might act as special "zeolites" that combine physical properties typical for semiconductors.

    In one instance, we have synthesized two new mesostructured metal germanium sulfides with hexagonal framework organization, incorporating [Ge4S10]4- anions and tetrahedral Ga3+ and In3+ cations. CP molecules act as templating agents and occupy the closest-packed cylindrical pores of the framework. The CPGaGeS and CPInGeS emit intense green light when excited across the band gap and presage the potential of such systems in light-emitting and optoelectronic devices. Current work focuses on experiments aimed at surfactant removal to render the pores in these systems accessible.
     
     

  4. Intermetallics from molten Al, Ga and In

 

Presentation

 

Development of molten metals and the application as solvents for exploratory synthesis and crystal growth

silicides, germanides

aluminides, others

Here again we approach this chemistry from a solution chemistís viewpoint rather than a conventional high temperature solid state chemistsís perspective. A key question to ponder here is: what happens to Si when it dissolves in liquid Al?

Recently we began investigating molten Al and Ga as potential solvents for the systematic exploratory synthesis of silicides, germanides, and related compounds. We reported that RE2Al3Si2 (RE = Y, Dy, Ho, Tm, Er), Sm2Ni(Si1-x,Nix)Al4Si6 and RENiAl4Ge2 (RE= Sm, Tb, Y) form readily in solutions of molten Al. In these reactions a solution of Si or Ge is formed in liquid Al which becomes available for reaction with other elements (e.g. rare earths, transition metals) to form ternary or quaternary compounds.


1. “REAu3Al7 (RE=rare earth): new ternary aluminides grown from aluminum flux” S. E. Latturner, D. Bilc, J. R. Ireland, C. R. Kannewurf, S. D. Mahanti and M. G. Kanatzidis J. Solid State Chem., 2003, 170, 48-57.

2. "Single Crystal X-ray Structure Investigation and Electronic Structure Studies of La-Deficient Nickel Stannide La4.87Ni12Sn24 Grown From Sn Flux" Marina A. Zhuravleva, Daniel Bilc, S. D. Mahanti, and Mercouri G. Kanatzidis, Z. Anorg. Allg. Chem. 2003, 629, 327-334.

3. "RE3Ga9Ge (RE = Y, Ce, Sm, and Gd): New Compounds with an Open Three-Dimensional Polygallide Framework Synthesized From Liquid Gallium." M. A. Zhuravleva and M. G. Kanatzidis, J. Solid State Chem., 2003, 173, 280-292.

4. “Stabilization of ?-SiB3 from Liquid Ga A Boron Rich Binary Semiconductor Resistant to High-Temperature Air Oxidation” J.R. Salvador, D. Bilc, S.D. Mahanti and M.G. Kanatzidis, Angew. Chemie, Int. Ed., 2003, 42, 1929–1932.

5. “Molten Ga as a Non-Reactive Solvent: Synthesis of Silicides RE2Ni3+xSi5-x (RE = Sm, Gd and Tb)” Marina A. Zhuravleva and Mercouri G. Kanatzidis, Z. Anorg. Allg. Chem., 2003, 58, 649-657.

6. “Eu10Mn6Sb13: A New Ternary Rare-Earth Transition Metal Zintl Phase” A. P. Holm, S.-M. Park, C L. Condron, H. Kim, P. Klavins, F. Grandjean, R. P. Hermann, G. J. Long, M. G. Kanatzidis, S. M. Kauzlarich, and S-J Kim, Inorg. Chem. 2003, 42, 4660-4667

7. “REMGa3Ge and RE3Ni3Ga8Ge3 (M=Ni, Co; RE=Rare-Earth Element): New Intermetallics Synthesized in Liquid Ga. X-Ray, Electron and Neutron Structure Determination and Magnetism” M. A. Zhuravleva, R. J. Pcionek, X. Wang, A. J. Schultz, and M. G. Kanatzidis, Inorg. Chem. 2003, 42, 6412-6424.

8. “Negative Thermal Expansion in YbGaGe via Electronic Valence Transition” J. R. Salvador, F. Guo, T. Hogan and M. G. Kanatzidis, Nature 2003, 425, 702 – 705.

9. “Ga-Ga Bonding and Tunnel Framework in the New Zintl Phase Ba3Ga4Sb5” S-M. Park, S-J Kim, and M. G. Kanatzidis, J. Solid State Chem., 2003, 175, 310-315.

10. “RE2MAl6Si4 (RE = Gd, Tb, Dy; M = Au, Pt): Layered quaternary intermetallics featuring CaAl2Si2-type and YNiAl4Ge2-type slabs grown from aluminum flux” Latturner S. E., Bilc D., Mahanti S. D., Kanatzidis, M. G. Inorg. Chem. 2003; 42, 7959-7966.

11. “REAu4Al8Si: the end member of a new homologous series of intermetallics featuring thick AuAl2 layers Latturner S. E., Kanatzidis M. G. Chem. Commun. 2003, 2340-2341.

12. "Formation of multinary intermetallics from reduction of perovskites by aluminum flux--M3Au6+xAl26Ti (M = Ca, Sr, Yb), a stuffed variant of the BaHg11 type" Latturner S. and Kanatzidis MG Inorg. Chem. 2004, 43, 2-4.

13. “Stabilization of new forms of the intermetallic phases ß-RENiGe2 (RE = Dy, Ho, Er, Tm, Yb, Lu) in liquid indium” Salvador J. R., Gour J. R., Bilc D., Mahanti S. D., Kanatzidis M. G. Inorg. Chem. 2004, 43, 1403-1410.

14. “V2Al5Ge5: first ternary intermetallic in the V-Al-Ge system accessible in liquid aluminium” Wu X., Bilc D., Mahanti S.D., and Kanatzidis M. G. Chem. Commun. 2004, 1506-1507.

15. “Intermetallics as zintl phases: Yb2Ga4Ge6 and RE3Ga4Ge6 (RE= Yb, Eu): Structural response of a [Ga4Ge6]4- framework to reduction by two electrons” Zhuravleva M. A., Salvador J., Bilc D., Mahanti S. D., Ireland, J. Kannewurf, C. R. and Kanatzidis M. G. Chem. Eur. J. 2004, 10, 3197-3208.

16. “Eu7Ga6Sb8: A Zintl phase with Ga-Ga bonds and polymeric gallium antimonide chains” Park S. M., Kim S. J., Kanatzidis M. G. J. Solid State Chem. 2004, 177, 2867-2874.

17. “Valence instabilities, phase transitions, and abrupt lattice expansion at 5 K in the YbGaGe system” Margadonna S., Prassides K., Fitch A. N., Salvador J.R., Kanatzidis M. G. J. Am. Chem. Soc. 2004, 126, 4498-4499.

18. “Yb8Ge3Sb5, a metallic mixed-valent Zintl phase containing the polymeric 1/8[Ge34-] anions” Salvador J. R., Bilc D., Mahanti S. D., Hogan T., Guo F., Kanatzidis M. G. J. Am. Chem. Soc. 2004, 126, 4474-4475.

19. “RE5Co4Si14 (RE = Ho, Er, Tm, Yb) Intermetallic Phases Grown from Ga Flux Showing Exceptional Resistance to Chemical and Thermal Attack” Salvador J. R., Malliakas C., Gour J. R. and Kanatzidis M. G., Chem. Mater. 2005, 17, 1636-1645.

20. “Tb4FeGe8 Grown in Liquid Gallium: Trans-cis chains from the distortion of a planar Ge square net” M. A. Zhuravleva, S Bilc, R. J. Pcionek, S. D. Mahanti and M. G. Kanatzidis, Inorg. Chem. 2005, 44, 2177-2188.21. “REAuAl4Ge2 and REAuAl4(AuxGe1-x)2 (RE=rare earth element): Quaternary intermetallics grown in liquid aluminum” X. Wu and M. G. Kanatzidis J. Solid State Chem. 2005, 178, 3233-3242.

22. “Intermetallic Compounds with Near Zintl Phase Behavior: RE2Zn3Ge6 (RE = La, Ce, Pr, and Nd) Grown from Liquid Indium” Salvador J. R., Bilc D., Gour J. R., Mahanti S. D., and Kanatzidis M. G., Inorg. Chem., 2005, asap article.

23. “The Metal Flux – A Preparative Tool for the Exploration of Intermetallic Compounds” M. G. Kanatzidis, R. Pöttgen, and W. Jeitschko, Angew. Chemie Int. Ed. 2005, 44, 6996-7023.

  1. Low-dimensional nano-composites between polymers and inorganic phases (nanoscience)
    The combination of two extremely different components, at the molecular level, provides an avenue to designing new nanocomposite hybrid materials as well as the ability to modulate the properties of one or more of the components. In some circumstances, it is also a unique way to generate materials which have special properties that are unknown in the individual components. Intercalation compounds with polymers as the guest species are an important class of nanocomposite materials. Intercalative polymer hybrids have advantages over their small molecular analogs in compositional stability and mechanical strength, which make them more suitable for certain applications. As a result of recent efforts, a large variety of intercalative nanocomposites have been prepared using hosts from most major classes of layered inorganic compounds, i.e., clays, layered transition metal chalcogenides, metal oxides, metal phosphates and metal thiophosphates.
     
     
  1. Hyrdothermal synthesis of novel metal chalcogenide compounds.
    2. We use hydrothermal and methanothermal techniques to investigate systems of the type: cation/metal/(AsxQy)z- (Q=S, Se) in order to discover new materials based on the sulfosalt family. We use the [AsQ3]3- and [SbQ3]3- anions as starting materials and explore their binding to metal ions in the presence of large organic or inorganic cations. The emphasis is on using superheated solvents. This approach leads to novel semiconducting materials with low dimensional framework structures. This is fundamental research with potential impact in several areas of materials science such as microporous semiconductors, photonic semiconductors, sulfide catalysts and intercalation chemistry.
     
     

    For examples of work in each of these areas see List of Publications and Selected Reprints.