Dr. Siméon Ponou


Dr. Siméon Ponou

Research Topic:

Complex Intermetallic Alloys: The Influence of Relativity

Support: Carl Tryggers Stiftelse

Contact: simeon.ponou1@mmk.su.se


Dr. Ponou’s current research takes advantage of the relativistic effects for the design of new class of (multi)functional materials. The main goal is to investigate the impact of relativity onto the chemistry of heavy elements by combining experimental work with computational studies synergistically. This will lead to a more general understanding how relativity affects chemistry, enhance the fundamental understanding of matter and ultimately allow for the design of unprecedented new materials by taking advantage of the relativistic effects. Dr. Ponou is primarily focusing on using relativistic effects to improve the performance of thermoelectric materials, as well as that of materials exhibiting giant magneto-caloric effects. In particular, he is investigating how metal–metal bonding frustration, driven by relativistic effects, induces valence state fluctuation coupled with structural transition in intermetallic compounds involving mixed-valent rare-earth metal like Yb and Eu. This is important for application in giant magnetocaloric effect, which is of interest in energy-efficient and environmentally friendly refrigerators, heat pumps, and thermomagnetic generators.

  1. Ponou S., Miller G. J. and Mudring A.-V. 2021. “Uncovering New Transition Metal Zintl Phases by Cation Substitution: The Crystal Chemistry of Ca3CuGe3 and Ca2+nMnxAg2–x+zGe2+nz (n = 3,4)”. CrystEngComm. 23(14): 2711-2722. DOI: 1039/d1ce00094b
  2. Shi Y., Assoud, A., Ponou, S., Lidin, S., Kleinke, H. 2018. “A New Material with a Composite Crystal Structure Causing Ultralow Thermal Conductivity and Outstanding Thermoelectric Properties: Tl2Ag12Te7+δ”. Journal of the American Chemical Society 140 (27), 8578–
  3. Ponou S., and S. Lidin. 2016. “Exo-bonded six-membered heterocycle in the crystal structures of RE7Co2Ge4 (RE=La–Nd).” Dalton Transactions 45(46), 18522–18531. DOI: 10.1039/c6dt03302d.
  4. Ponou S., S. Lidin, D. Grüner, and G. J. Miller. 2016. “Conflict between the Electronic Factors and Structure-Directing Rules in the Intergrowth Structure of Ca4Ag2+xGe4–xwith x = 1/2” Crystal Growth & Design 16(10): 5946-5953. DOI: 1021/acs.cgd.6b01002.
  5. Ponou S., I. Doverbratt, S. Lidin, and G. J. Miller. 2016. “Structure and Bonding of an Intergrowth Phase Ca7Ag2+xGe7–x(x ≈ 2/3) Featuring a Zintl-Type Polyanionic Chain.” European Journal of Inorganic Chemistry 2016 (1), 169-176.
  6. Doverbratt I., Ponou, F. Wang, and S. Lidin. 2015. “Synthesis, Crystal Structure, and Bonding Analysis of the Hypoelectronic Cubic Phase Ca5Pd6Ge6.”Inorganic Chemistry 54 (18): 9098-9104.
  7. Ponou, S. and G. J. Miller. 2015. “Synergistic Geometrical and Electronic Features in the Intermetallic Phases Ca2AgM2, Ca2MgM2, and Ca2GaM2 (M = Pd, Pt).”Zeitschrift Fur Anorganische Und Allgemeine Chemie 641(6): 1069-1079.
  8. Doverbratt, I., Ponou, Y. Zhang, S. Lidin, and G. J. Miller. 2015. “Linear Metal Chains in Ca2M2X (M = Pd, Pt; X = Al, Ge): Origin of the Pairwise Distortion and its Role in the Structure Stability.” Chemistry of Materials27(1): 304-315.
  9. Ponou, S., S. Lidin, Y. Zhang, and G. J. Miller. 2014. “Valence State Driven Site Preference in the Quaternary Compound Ca5MgAgGe5: An Electron-Deficient Phase with Optimized Bonding.” Inorganic Chemistry53(9): 4724-4732.
  10. Kenfack Tsobnang, P., E. Wenger, S. Ponou, S. Dahaoui, J. Lambi Ngolui, and C. Lecomte. 2014.” A New Heteroleptic Oxalate-Based Compound: Poly[[2-(Amino-Meth-Yl)Pyridine] Di-μ6-Oxalato-Chromium(III)Potassium(I)].” Acta Crystallographica Section C: Structural Chemistry70(1): 12-15.
  11. Kenfack Tsobnang, P., E. Wenger, C. Biache, J. Lambi Ngolui, Ponou, S. Dahaoui, and C. Lecomte. 2014. “Two-Dimensionally Stacked Heterometallic Layers Hosting a Discrete Chair Dodecameric Ring of Water Clusters: Synthesis and Structural Study.” Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials70(5): 900-902.
  12. Ponou, S. and S. Lidin. 2013. “Ca3Ag1+xGe3-x (x = 1/3): New Transition Metal Zintl Phase with Intergrowth Structure and Alloying with Aluminum Metal.” Zeitschrift Für Anorganische Und Allgemeine Chemie639 (1): 35-40.
  13. Fredrickson, D. C., I. Doverbratt, Ponou, and S. Lidin. 2013. “Bonding Schemes for Polar Intermetallics through Molecular Orbital Models: Ca-Supported Pt-Pt Bonds in Ca10Pt7Si3.” Crystals3 (3): 504-516.
  14. Doverbratt, I., Ponou, and S. Lidin. 2013. “Ca2Pd3Ge, a New Fully Ordered Ternary Laves Phase Structure.” Journal of Solid State Chemistry197: 312-316.
  15. Ngoune, J., C. Di Nicolas, J. Nenwa, C. Pettinari, E. Alvarez, and Ponou. 2013. “A Supramolecular Copper(II) Compound with Double Bridging Water Ligands: Synthesis, Crystal Structure, Spectroscopy, Thermal Analysis, and Magnetism.” Transition Metal Chemistry38 (1): 21-29.
  16. Doverbratt, I., S. Ponou, S. Lidin, and D. C. Fredrickson. 2012. “Ca10Pt7Tt3 (Tt = Si, Ge): New Platinide Phases Featuring Electron-Rich 4c-6e Bonded [Pt7Tt3]20– Intermetalloid Clusters.” Inorganic Chemistry51 (21): 11980-11985.
  17. Hlukhyy, V., T. F. Fässler, Ponou, S. Lidin, N. P. Ivleva, and R. Niessner. 2012. “Extreme Differences in Oxidation States: Synthesis and Structural Analysis of the Germanide Oxometallates A10[Ge9]2[WO4] as Well as A10+x[Ge9]2[W1-xNbxO4] with A = K and Rb Containing [Ge9]4- Polyanions.” Inorganic Chemistry51 (7): 4058-4065.
  18. Bélombé, M. M., J. Nenwa, J. S. T. Wankap Kouamo, Ponou, and A. Fischer. 2012. “Catena-Poly[[[(Oxamide Dioxime-κ2N,N′)Copper(II)] -μl-Tartrato-κ4O1,O2:O3,O4] Tetra-Hydrate]: A Chiral Nanochannel Framework Hosting Solvent Water Molecules.” Acta Crystallographica Section C: Crystal Structure Communications68 (5): m131-m134.
  19. Åkerstedt, J., Ponou, L. Kloo, and S. Lidin. 2011. “Structural Investigation of a Fully Ordered Closo-Ge92– Cluster in the Compound [K+(2,2,2-Crypt)]2Ge92–.” European Journal of Inorganic Chemistry(26): 3999-4005.
  20. Kenfack Tsobnang, P., D. Fotio, Ponou, and C. Fon Abi. 2011. “Calcium Platinum Aluminium, CaPtAl.” Acta Crystallographica Section E: Structure Reports Online67 (10).
  21. Ponou, S. 2010. “On a TiNiSi-Type Superstructure: Synthesis, Crystal and Electronic Structures of CaAgGe and its Mn-Substituted Derivative.” European Journal of Inorganic Chemistry(26): 4139-4147.
  22. Ponou, S., S.-J. Kim, and T. F. Fässler. 2009. “Synthesis and Characterization of Na5M2+xSn10-x (x ≈ 0.5, M = Zn, Hg) – A Doped Tetrahedral Framework Structure.” Journal of the American Chemical Society131 (29): 10246-10252.
  23. Ponou, S. and S. Lidin. 2009. “Synthesis and Crystal Structure of Ca2Ag83Al0.67Ge1.50 – A Solid Solution with the NbCoB-Type Structure.” Zeitschrift Für Anorganische Und Allgemeine Chemie 635 (13-14): 2143-2146.
  24. Ponou, S. and S. Lidin. 2009. “α-Cd13-xSb10 – The Devil is in the Details.” Zeitschrift Für Anorganische Und Allgemeine Chemie 635 (12): 1747-1752.
  25. Banenzoué, C., Ponou, and J. N. Lambi. 2009. “Nonisovalent Substitution in a Zintl Phase with the TiNiSi Type Structure, CaMg1-xAgxGe [x = 0.13 (3)].”Acta Crystallographica Section E: Structure Reports Online 65 (12).
  26. Kim, S. -J, Ponou, and T. F. Fässler. 2008. “Cation Substitution Effects in the System Sr2-xBaxBi3 (0 ≤ x ≤ 1.3): Structural Distortions Induced by Chemical Pressure.” Inorganic Chemistry47 (9): 3594-3602.
  27. Kaltzoglou, A., Ponou, and T. F. Fässler. 2008. “A4Ge9 (A = K, Rb) as Precursors for Hg-Substituted Clathrate-I Synthesis: Crystal Structure of A8Hg3Ge43.” European Journal of Inorganic Chemistry (29): 4507-4510.
  28. Kaltzoglou, A., Ponou, and T. F. Fässler. 2008. “Synthesis and Crystal Structure of Mercury-Substituted Type-I Clathrates A8Hg4Sn42 (A = K, Rb, Cs).” European Journal of Inorganic Chemistry (4): 538-542.
  29. Ponou, S. and S. Lidin. 2008. “Crystal Structure of Calcium Silver Germanium, CaAg98Ge1.02.” Zeitschrift Fur Kristallographie – New Crystal Structures223 (4): 329-330.
  30. Ponou, S., T. F. Fässler, and L. Kienle. 2008. “Structural Complexity in Intermetallic Alloys: Long-Periodic Order Beyond 10 nm in the System BaSn3/BaBi3.” Angewandte Chemie – International Edition47 (21): 3999-4004.
  31. Ponou, S., S. -J Kim, and T. F. Fässler. 2007. “Substitution Effects in Zintl Phases: Synthesis and Crystal Structure of the Novel Phases Ae3Sn4-xBi1-x (x ≤ 1; Ae = Sr, Ba) Ontaining Shubnikov-Type Nets [Sn4-xBix].” Zeitschrift Für Anorganische Und Allgemeine Chemie633 (10): 1568-1574.
  32. Ponou, S. and T. F. Fässler. 2007. “Crystal Growth and Structure Refinement of K4Ge9.” Zeitschrift Für Anorganische Und Allgemeine Chemie 633 (3): 393-397.
  33. Ponou, S., N. Müller, T. F. Fässler, and U. Häussermann. 2005. “KBi2-xPbx (0 < x ≤ 1): A Zintl Phase Evolving from a Distortion of the Cubic Laves-Phase Structure.” Inorganic Chemistry44 (21): 7423-7430.
  34. Ponou, S. and T. F. Fässler. 2004. “Nonclassical Bonding in the Novel Structure of Ba2Bi3 and Unexpected Site Preference in the Coloring Variant Ba2BiSb2.” Inorganic Chemistry43 (20): 6124-6126.
  35. Ponou, S., T. F. Fässler, G. Tobías, E. Canadell, A. Cho, and S. C. Sevov. 2004. “Synthesis, Characterization, and Electronic Structure of Ba5In4Bi5: An Acentric and One-Electron Deficient Phase.” Chemistry – A European Journal10 (15): 3615-3621.
  36. Woike, T., S. Dahaoui, D. Schaniel, Ponou, N. K. Hansen, and V. Petricek. 2004. “Structure Analysis and the Existence of Light-Induced Long-Lived Metastable States in Xn[Fe(CN)5NO] with Inorganic and Organic Cations: Xn = Pb, (H3O+CH6N+), (C2N2H7)2 and (C16H36N)2.” Zeitschrift Fur Kristallographie219 (9): 558-566.