960化工网
Thermal expansion tensors, Grüneisen parameters and phonon velocities of bulk MT2 (M = W and Mo; T = S and Se) from first principles calculations
Yingchun Ding,Bing Xiao
RSC Advances Pub Date : 02/06/2015 00:00:00 , DOI:10.1039/C4RA16966B
Abstract

We calculated the phonon spectra of several 2H-MT2 structures using the density functional perturbation theory (DFPT). The symmetry properties of phonon modes are analyzed. The mode-Grüneisen parameters and phonon velocities are calculated using phonon spectra. All the investigated structures show very large phase velocities (>10 000 m s−1) and small group velocities (<600 m s−1). The macroscopic Grüneisen parameter of the [001] direction is larger than that of the [010] direction for 2H-MT2 phases. The volumetric and linear thermal expansion coefficients are evaluated using the quasi-harmonic approximation (QHA) between 0 K and 1100 K. The negative thermal expansion coefficients are discovered in the 2H-WS2 structure. Our results show that the properties in the [001] direction are very different to the [010] direction, because of the significant difference in the chemical bonding in the two crystallographic directions for these layered materials.

Graphical abstract: Thermal expansion tensors, Grüneisen parameters and phonon velocities of bulk MT2 (M = W and Mo; T = S and Se) from first principles calculations
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