Vibrational and Thermal Properties of Ag3[Co(CN)6] from First Principles Calculations and Infrared Spectroscopy

Patrick Hermet (1) , Jadna Catafesta (2, 1) , Jean-Louis Bantignies (2) , Claire Levelut (2) , David Maurin (2) , A. B. Cairns (3) , A. L. Goodwin (3) , Julien Haines (1)

1 ICGM ICMMM - Institut Charles Gerhardt Montpellier - Institut de Chimie Moléculaire et des Matériaux de Montpellier
2 L2C - Laboratoire Charles Coulomb
3 Univ Oxford, Inorgan Chem Lab, Dept Chem, Oxford OX1 3QR

We have investigated the phonon modes of Ag-3[Co(CN)(6)] using first-principles based methods and high-pressure infrared spectroscopy to understand the origin of its colossal thermal expansion. Griineisen parameters of its zone-center vibrational modes were obtained from the calculations and compared to the experimental ones. We found that optical phonon modes below 100 cm(-1) mainly contribute to its negative thermal expansion, and they also have a significant mixing with acoustic branches. These modes have been assigned to translational motion of the Co-CN-Ag-NC-Co linkages. We also identify a pressure-induced softening of zone-center phonon modes that could account for the experimentally observed phase transition in terms of a first-order displacive instability from the trigona1P-3-1m space group to the acentric Cm space group.

Domaines: Matériaux

Patrick Hermet, Jadna Catafesta, Jean-Louis Bantignies, Claire Levelut, David Maurin, et al.. Vibrational and Thermal Properties of Ag3[Co(CN)6] from First Principles Calculations and Infrared Spectroscopy. Journal of Physical Chemistry C, 2013, 117, pp.12848. ⟨10.1021/jp402081r⟩. ⟨hal-00903684⟩