Top Banner
Ag 3 [Co(CN) 6 ]: Giant Positive and Negative Thermal Expansion Elizabeth A. Clark Materials 286G May 26, 2010
11

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

Dec 16, 2015

Download

Documents

Fernando Dopson
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: Ag 3 [Co(CN) 6 ]: Giant Positive and Negative Thermal Expansion Elizabeth A. Clark Materials 286G May 26, 2010.

Ag3[Co(CN)6]: Giant Positive and Negative Thermal Expansion

Elizabeth A. ClarkMaterials 286GMay 26, 2010

Page 2: Ag 3 [Co(CN) 6 ]: Giant Positive and Negative Thermal Expansion Elizabeth A. Clark Materials 286G May 26, 2010.

2

Thermal Expansion: A result of Anharmonicity in Bond Vibrations

http://www.ami.ac.uk/courses/topics/0197_cte/images/ch_cte_imga.gif

• Thermal expansion occurs in most materials because of the anharmonicity of the bond vibrations

•The bond length increases as temperature increases

r r

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

3

Negative Thermal Expansion due to Transverse Vibrations

α ≈ -9x10-6 /K

ZrO6 OctahedraZrW2O8

J. S. O. Evans et al., Chem. Mater., 8 [12], 2809–2823

Page 4: Ag 3 [Co(CN) 6 ]: Giant Positive and Negative Thermal Expansion Elizabeth A. Clark Materials 286G May 26, 2010.

4

Ag3[Co(CN)6]: Structure

A.L. Goodwin et al., Science, 319, 794-797

Cobalt sits in carbon octahedra. Planes of silver sit between the octahedra, and are connected by nitrogen.

P3 1mRhombahedral

Page 5: Ag 3 [Co(CN) 6 ]: Giant Positive and Negative Thermal Expansion Elizabeth A. Clark Materials 286G May 26, 2010.

5

Ag3[Co(CN)6]: Connectivity

CoNCNC CN

CN

CN

NCAg NC

Bonding along <101> directions

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

6

Ag3[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)

AgAg ≈ 3.4Å

Page 7: Ag 3 [Co(CN) 6 ]: Giant Positive and Negative Thermal Expansion Elizabeth A. Clark Materials 286G May 26, 2010.

7

Ag3[Co(CN)6]: Colossal Thermal Expansion/Contraction

130x10-6/K < αa < 150x10-6/K-120x10-6/K < αc < -130x10-6/K

αAg…Co ≈ 0/KA.L. Goodwin et al., Science, 319, 794-797

Page 8: Ag 3 [Co(CN) 6 ]: Giant Positive and Negative Thermal Expansion Elizabeth A. Clark Materials 286G May 26, 2010.

8

Argentophilic Interactions Drive Colossal PTE/NTE

A.L. Goodwin et al., Science, 319, 794-797

A: Lattice enthalpy from density functional calculations ()

B: Mean partial phonon frequencies: CN Δ Co Ag

Page 9: Ag 3 [Co(CN) 6 ]: Giant Positive and Negative Thermal Expansion Elizabeth A. Clark Materials 286G May 26, 2010.

9A.L. Goodwin et al., J. Am. Chem. Soc., 130 [30], 9660-9661

Argentophilic Interactions Drive Colossal PTE/NTE

Page 10: Ag 3 [Co(CN) 6 ]: Giant Positive and Negative Thermal Expansion Elizabeth A. Clark Materials 286G May 26, 2010.

10J.L. Korčok, M.J. Katz, D.B. Leznoff, J. Am. Chem. Soc., 131, 4866-4871

Strength of Metallophilic Interactions Affect Thermal Expansion

Page 11: Ag 3 [Co(CN) 6 ]: Giant Positive and Negative Thermal Expansion Elizabeth A. Clark Materials 286G May 26, 2010.

11

• Increases in bond length with increasing temperature is a result of the anharmonicity of bond vibrations

• Transverse vibrations can cause negative thermal expansion• Ag3[Co(CN)6] exhibits colossal positive and negative thermal

expansion– Flexible framework– Ag…Ag interactions

Conclusions