Ab initiolattice dynamical studies of silicon clathrate frameworks and their negative thermal expansion

Abstract

The thermal and lattice dynamical properties of seven silicon clathrate framework structures are investigated with ab initio density functional methods (frameworks I, II, IV, V, VII, VIII, and H). The negative thermal expansion (NTE) phenomenon is investigated by means of quasiharmonic approximation and applying it to equal time displacement correlation functions. The thermal properties of the studied clathrate frameworks, excluding the VII framework, resemble those of the crystalline silicon diamond structure. The clathrate framework VII was found to have anomalous NTE temperature range up to 300 K and it is suitable for further studies of the mechanisms of NTE. Investigation of the displacement correlation functions revealed that in NTE, the volume derivatives of the mean square displacements and mean square relative displacements of atoms behave similarly to the vibrational entropy volume derivatives and consequently to the coefficients of thermal expansion as a function of temperature. All studied clathrate frameworks, excluding the VII framework, possess a phonon band gap or even two in the case of the framework V.

Ab initiostudies on the lattice thermal conductivity of silicon clathrate frameworks II and VIII

“…Figure 2 shows the calculated phonon dispersion relations for the clathrate structures II and VIII. As in the case of d-Si, similar results are obtained by using the present computational methods or LDA with Martins-Troullier-type norm-conserving pseudopotentials [43]. From the similar phonon dispersion relations of the clathrate structures II and VIII, it follows that their thermal properties within the harmonic approximation are rather similar, as well.…”

“…Similar computational results have been obtained earlier by using both local density approximation (LDA) and GGA with the plane-wave pseudopotential method [39][40][41][42]. The maximum difference between the eigenvalues obtained here and the eigenvalues obtained by using LDA with Martins-Troullier-type normconserving pseudopotentials is approximately 10% [43]. Figure 2 shows the calculated phonon dispersion relations for the clathrate structures II and VIII.…”

Ab initiocomputational study on the lattice thermal conductivity of Zintl clathrates[Si19P4]Cl4andHärkönen1, Karttunen2 2016Phys. Rev. BSelf Cite11190View full textAdd to dashboardCite

“…That is, {γ μν (λ)} are usually expected to have relatively large absolute values for materials that have rather large absolute value of the CTE. There is some evidence that the silicon clathrate framework VII possesses rather unusual NTE behavior, while Si 23 (or VIII), for instance, has CTE that is rather similar to d-Si [72].…”

Lattice dynamics and thermal expansion behavior in the metal cyanidesMCN(M=Cu, Ag, Au): Neutron inelastic scattering and first-principles calculations

“…The cyanide compounds are found to exhibit the phenomenon of negative linear compressibility. The c-axis in Ag 3 Co(CN) 6 is found to show NTE as well as negative linear compressibility 9,18,[34][35][36][37] behavior. KMn[Ag(CN) 2 ] 3 shows extreme negative compressibility mediated by selective soft-mode frustration 38 .…”