Phonons and Colossal Thermal Expansion Behavior of Ag3Co(CN)6 and Ag3Fe(CN)6

Abstract

Recently colossal positive volume thermal expansion has been found in the framework compounds Ag3Co(CN)6 and Ag3Fe(CN)6. Phonon spectra have been measured using the inelastic neutron scattering technique as a function of temperature and pressure. The data has been analyzed using ab-initio calculations. We find that the bonding is very similar in both compounds. At ambient pressure modes in the intermediate frequency part of the vibrational spectra in the Co compound are shifted to slightly higher energies as compared to the Fe compound. The temperature dependence of the phonon spectra gives evidence for large explicit anharmonic contribution to the total anharmonicity for low-energy modes below 5 meV. We found that modes are mainly affected by the change in the size of unit cell, which in turn changes the bond lengths and vibrational frequencies. Thermal expansion has been calculated via the volume dependence of phonon spectra. Our analysis indicates that Ag phonon modes in the energy range from 2 to 5 meV are strongly anharmonic and major contributors to thermal expansion in both compounds. The application of pressure hardens the low-energy part of the phonon spectra involving Ag vibrations and confirms the highly anharmonic nature of these modes.

19 pages, 14 figures and one table

References in corpus (1)

• Relationship Between Phonons and Thermal Expansion in Zn(CN)2 and Ni(CN)2 from Inelastic Neutron Scattering and Ab-Initio Calculations

Cited by in corpus (6)

• Negative Thermal Expansion in cubic ZrW2O8: Role of Phonons in Entire Brillouin Zone From ab-inito Calculations
• The Ag...Ag dispersive interaction and exotic physical properties of Ag3Co(CN)6
• Lattice dynamics and negative thermal expansion in the framework compound ZnNi(CN)${}_4$ with two-dimensional and three-dimensional local environments
• Phonon dynamics in the layered negative thermal expansion compounds Cu${}_x$Ni${}_{2-x}$(CN)${}_4$
• Negative thermal expansion and metallophilicity in Cu${}_3$[Co(CN)${}_6$]
• Anomalous thermal expansion in one-dimensional transition-metal cyanides: Behavior of the trimetallic cyanide Cu${}_{1/3}$Ag${}_{1/3}$Au${}_{1/3}$CN