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Ag 3 [Co(CN) 6 ]: Giant Positive and Negative Thermal Expansion Elizabeth A. Clark Materials 286G May 26, 2010.

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Presentation on theme: "Ag 3 [Co(CN) 6 ]: Giant Positive and Negative Thermal Expansion Elizabeth A. Clark Materials 286G May 26, 2010."— Presentation transcript:

1 Ag 3 [Co(CN) 6 ]: Giant Positive and Negative Thermal Expansion Elizabeth A. Clark Materials 286G May 26, 2010

2 2 Thermal Expansion: A result of Anharmonicity in Bond Vibrations Thermal expansion occurs in most materials because of the anharmonicity of the bond vibrations The bond length increases as temperature increases r r

3 3 Negative Thermal Expansion due to Transverse Vibrations α ≈ -9x10 -6 /K ZrO 6 Octahedra ZrW 2 O 8 J. S. O. Evans et al., Chem. Mater., 8 [12], 2809–2823

4 4 Ag 3 [Co(CN) 6 ]: Structure A.L. Goodwin et al., Science, 319, Cobalt sits in carbon octahedra. Planes of silver sit between the octahedra, and are connected by nitrogen. Rhombahedral

5 5 Ag 3 [Co(CN) 6 ]: Connectivity Co NCNC NCNC CNCN CNCN CNCN NCNC Ag NCNC Bonding along directions

6 6 Ag 3 [Co(CN) 6 ]: Connectivity Ag + ions sit on the vertices of a Kagome lattice Argentophilicity – weak Ag-Ag interactions, (In case of Au-Au, similar in strength to hydrogen bonds) Ag  Ag ≈ 3.4Å

7 7 Ag 3 [Co(CN) 6 ]: Colossal Thermal Expansion/Contraction 130x10 -6 /K < α a < 150x10 -6 /K -120x10 -6 /K < α c < -130x10 -6 /K α Ag…Co ≈ 0/K A.L. Goodwin et al., Science, 319,

8 8 Argentophilic Interactions Drive Colossal PTE/NTE A.L. Goodwin et al., Science, 319, A: Lattice enthalpy from density functional calculations () B: Mean partial phonon frequencies: CN Δ Co Ag

9 9 A.L. Goodwin et al., J. Am. Chem. Soc., 130 [30], Argentophilic Interactions Drive Colossal PTE/NTE

10 10 J.L. Korčok, M.J. Katz, D.B. Leznoff, J. Am. Chem. Soc., 131, Strength of Metallophilic Interactions Affect Thermal Expansion

11 Increases in bond length with increasing temperature is a result of the anharmonicity of bond vibrations Transverse vibrations can cause negative thermal expansion Ag 3 [Co(CN) 6 ] exhibits colossal positive and negative thermal expansion – Flexible framework – Ag…Ag interactions 11 Conclusions


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