Anomalous Lattice Dynamics in AgC4N3: Insights From Inelastic Neutron Scattering and Density Functional Calculations

Abstract

We have performed temperature dependent inelastic neutron scattering measurements to study the anharmonicity of phonon spectra of AgC4N3. The analysis and interpretation of the experimental spectra is done using ab-initio lattice dynamics calculations. The calculated phonon spectrum over the entire Brillouin zone is used to derive linear thermal expansion coefficients. The effect of van der Waals interaction on structure stability has been investigated using advanced density functional methods. The calculated isothermal equation of states implies a negative linear compressibility along the c-axis of the crystal, which also leads to a negative thermal expansion along this direction. The role of elastic properties inducing the observed anomalous lattice behavior is discussed.

Lattice dynamics and negative thermal expansion in the framework compound ZnNi(CN)4 with two-dimensional and three-dimensional local environments

“…The Q-averaged, one-phonon generalized phonon density of states (GDOS) [23], g (n) (E), was obtained using the incoherent approximation [25,26]. This method has been used previously to investigate phonon dynamics and anomalous thermal expansion in a number of transition-metal cyanides [9,11,13,47,27]. In the incoherent, one-phonon approximation, g (n) (E) is related to the measured scattering function S(Q, E) from INS by where A is a normalization constant, 2W(Q) is the Debye-Waller factor and n(E,T) is the thermal occupation factor equal to [exp(E/kBT-1)] -1 .…”