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Unconventionality in Solid State Chemistry

Unconventionality in Solid State Chemistry. Douglas A. Vander Griend Department of Chemistry & Biochemistry Calvin College Grand Rapids, Michigan July 7, 2004. Unconventional. ŭn΄kën-věn΄shë-nël/ adjective not bound by or in accordance with convention being out of the ordinary

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Unconventionality in Solid State Chemistry

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  1. Unconventionality in Solid State Chemistry Douglas A. Vander Griend Department of Chemistry & Biochemistry Calvin College Grand Rapids, Michigan July 7, 2004

  2. Unconventional • ŭn΄kën-věn΄shë-nël/ adjective • not bound by or in accordance with convention • being out of the ordinary • existing without precedent

  3. Conventional Solid State Structures

  4. Conventional Compositions

  5. Idealized Subcell for La3Cu2VO9 [A] [BO2+3/3] [A] [La] [(Cu/V)O2+3/3] [La]

  6. La3Cu2VO9 Superstructure CuII 87% Cu VV O2- P63/m a = 14.448(1) Å c = 10.686(1) Å

  7. La3Cu2VO9: Frustrated Antiferromagnetism 1.68 mB 1.14 mB 100% Paramagnetic Inverse Molar Susceptibility (per copper) 0.56 mB 54% Paramagnetic 16% 0 100 300 400 200 Temperature (K)

  8. LaxLn3-xCu2VO9 Lattice Parameters

  9. Idealized Subcell of La4Cu3MoO12 [A] [BO2+3/3] [A] [La] [(Cu/Mo)O2+3/3] [La]

  10. Electron Diffraction • La4Cu3MoO12Ordering of the B-cations leads to a monoclinic supercell (g = 90.03(1)º) which is 4 times larger than the conventional hexagonal subcell. • La3Cu2VO9*Ordering of the B-cations leads to a hexagonal supercell which is 13 times larger than the conventional hexagonal subcell. *K. Jansson, I. Bryntse, Y. Teraoka Mater. Res. Bull., 1996, 31, 827.

  11. La4Cu3MoO12: B-cation Ordering

  12. La4Cu3MoO12: Frustrated Antiferromagnetism 1.73 mB Inverse Molar Susceptibility (per copper) 100% Paramagnetic 1.02 mB 35% Paramagnetic Temperature (K)

  13. Ln4Cu3MoO12 Powder X-ray Diffraction

  14. Ln4Cu3MoO12 Lattice Parameters

  15. Rare-earth Hexagonal Structure Type Versatility Ln4Cu3MoO12 Ln = La, Pr, Nd, Sm - Tm "Many new and novel compositions and structures remain to be discovered by more traditional means." -J.D. Corbett Ln2CuTiO6 Ln = Tb – Lu* Ln3Cu2VO9 Ln = La, Pr, Nd, Sm - Gd *Prog. Solid St. Chem. 1993, 22, 197.

  16. Formation of Single Phases • The primary goal of state synthesis is to form single phases • Single phases form if and only if their G is less than all possible multiphase mixtures at the reaction temperature. • The following examples demonstrate the importance of stoichiometric analysis in the search for novel materials.

  17. An Expected Result

  18. An Unexpected Result

  19. Thermodynamic Hierarchy G G(La2MoO6 + Ho2Cu2O5) < G(Ho2MoO6 + La2Cu2O5) Ln2Cu2O5 is more stable for smaller lanthanides, and/or Ln2MoO6 is more stable for larger lanthanides.

  20. Ln'2Ln"2Cu3MoO12 Synthesis Results

  21. Why does La4Cu3MoO12 Form? • Structure is unconventional. • A-cation coordination is low (6-7). • B-cation coordination is atypical (trigonal bipyramidal). • But La2+2nCu4+nO7+4n (n = 2) is worse! • “It is remarkable that, given the simple ratio of the constituent elements, such complex structures form instead of the structurally simpler Ruddleson-Popper series.” - Cava et al. 1991. • Ln2Cu2O5 is not even known for Ce – Gd. • 75% copper is sufficient to promote single phase. • La4Cu3MoO12 forms so that La2Cu2O5 doesn’t.

  22. The La2Cu2O5 Umbrella Stoichiometry

  23. La4Cu3+xMo1-xO12

  24. Why does Ho4Cu3MoO12 Form? • Ho2Cu2O5 isn’t the problem anymore. • Ho2MoO6 + CuO is the problem! • Ln2MoO6 changes structure between Nd and Sm. • 25% molybdenum is sufficient to promote single phase. • Ho4Cu3MoO12 forms so that Ho2MoO6 doesn’t.

  25. Ln2MoO6 Structural Shift Nd2MoO6 (I-42m) a = 4.0010 Å c = 15.7950 Å Sm2MoO6 (I2/a) a = 15.76 Å b = 11.26 Å c = 5.467 Å 2 (copper K)

  26. Ln4(Cu/Mo)4O12 Thermodynamic Stability

  27. More Examples • La2CuSnO6 vs. La2Cu2O5 + La2Sn2O7 • La2Sn2O7, stable pyrochlore, infamous thermodynamic sink • La2CuSnO6, lone example of a layered double perovskite that forms at ambient pressure. • La2Ba2Cu2Ti2O11 vs. La2Cu2O5 + 2BaTiO3 • La2Ba2Cu2Ti2O11, layered quadruple perovskite • BaTiO3, well known for centuries. • All known phases exist because at least one of the phases in every multiphase alternative has a sufficiently high G. • Identifying and applying these Umbrella Stoichiometries is the key to a more rational search for novel matierals.

  28. Conclusions – searching for unconventionality • Umbrella stoichiometries promote single phase results by destabilizing multiphase alternatives. • Umbrella stoichiometries facilitate substitutions that shift compositions towards them. Example: La4Cu3+xMo1-xO12-2x 0  x  0.12 • Undiscovered phases likely exist near umbrella stoichiometries. • Phases discovered near umbrella stoichiometries will tend to be unconventional because they can be structurally discontent and still be the thermodynamic product of a solid state reaction.

  29. Chemistry Department Kenneth R. Poeppelmeier Dr. Kenji Otzschi Dr. Donggeun Ko Dr. Sophie Boudin Dr. Vincent Caignaert Dr. Sylvie Malo Dr. Antoine Maignan Tony Wang Noura Dabbouseh Scott Barry Materials Science Department Prof. Thomas Mason Dr. Yanguo Wang Prof. Vinayak Dravid Kyoto University Prof. Mikio Takano Dr. Masaki Azuma Hiroki Toganoh Argonne National Laboratory Dr. Simine Short Dr. Zhongbo Hu Dr. James Jorgensen Funding Science and Technology Center for Superconductivity Japan Society for the Promotion of Science National Science Foundation Graduate Fellowship Acknowledgements

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