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.
Highlights
A few crystalline materials are found to exhibit expansion along certain crystallographic axes on application of static pressure (Goodwin et al, 2008a; Cairns et al, 2012, 2013; Cairns and Goodwin, 2015; Gupta et al, 2017; Yeung et al, 2017)
We found that including van der Walls (vdW) interaction describes better the structure whose calculated lattice parameters agree with the experimental
Ab-initio calculations performed at various uniform hydrostatic pressures are used to obtain the compressibility of the compound
Summary
A few crystalline materials are found to exhibit expansion along certain crystallographic axes on application of static pressure (Goodwin et al, 2008a; Cairns et al, 2012, 2013; Cairns and Goodwin, 2015; Gupta et al, 2017; Yeung et al, 2017). Phonons in the entire Brillouin zone calculated using the ab-initio lattice dynamics in combination with the elastic properties have successfully been used to reproduce the experimental values of anisotropic linear thermal expansion coefficients (Gupta et al, 2013, 2016, 2017; Singh et al, 2017a,b; Mittal et al, 2018). We have performed the analysis of specific phonon modes to gain insights into the atomic level mechanisms at the origin of the observed negative thermal expansion behavior along the c-axis.
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