Phonons and Anomalous Lattice Behaviour in KMnAg3(CN)6 and KNiAu3(CN)6: Inelastic Neutron Scattering and First-Principles Calculations

TL;DR

This study investigates phonon behavior and anomalous lattice properties in cyanide framework compounds KMnAg3(CN)6 and KNiAu3(CN)6, revealing negative thermal expansion and negative linear compressibility through experiments and first-principles calculations.

Contribution

It provides new insights into the phonon-driven negative thermal expansion and lattice anomalies in cyanide frameworks, incorporating the effects of van der Waals and magnetic interactions.

Findings

Observation of negative thermal expansion linked to low-energy phonons.

Detection of negative linear compressibility under isotropic compression.

Validation of phonon spectra with inelastic neutron scattering data.

Abstract

Cyanide based framework compounds are known to show large negative thermal expansion behaviour. Here we report the phonon and anomalous lattice behavior of two metal cyanide framework compounds i.e. KMnAg3(CN)6 and KNiAu3(CN)6. We have studied the role of van der Waals dispersion and magnetic interactions on structural stability of these compounds. The behavior of these compounds under isotropic compression shows the presence of negative linear compressibility. The calculated phonon spectra, validated by inelastic neutron scattering measurements and elastic constants are used to study the negative thermal expansion behavior which is found to arise from low energy phonon modes involving the folding of A-NC-B-CN-A linkage about B atoms.