TY - JOUR
T1 - Effect of guest atom composition on the structural and vibrational properties of the type II clathrate-based materials AxSi136, AxGe136 and AxSn136 (A = Na, K, Rb, Cs; 0 ≤ x ≤ 24)
AU - Xue, Dong
AU - Myles, Charles W.
AU - Higgins, Craig
N1 - Publisher Copyright:
© 2016 by the authors.
PY - 2016/8/11
Y1 - 2016/8/11
N2 - Type II clathrates are interesting due to their potential thermoelectric applications. Powdered X-ray diffraction (XRD) data and density functional calculations for NaxSi136 found a lattice contraction as x increases for 0 < x < 8 and an expansion as x increases for x > 8. This is explained by XRD data that shows that as x increases, the Si28 cages are filled first for x < 8 and the Si20 cages are then filled for x > 8. Motivated by this work, here we report the results of first-principles calculations of the structural and vibrational properties of the Type II clathrate compounds AxSi136, AxGe136, and AxSn136. We present results for the variation of the lattice constants, bulk moduli, and other structural parameters with x. These are contrasted for the Si, Ge, and Sn compounds and for guests A = Na, K, Rb, and Cs. We also present calculated results of phonon dispersion relations for Na4Si136, Na4Ge136, and Na4Sn136 and we compare these for the three materials. Finally, we present calculated results for the elastic constants in NaxSi136, NaxGe136, and NaxSn136 for x = 4 and 8. These are compared for the three hosts, as well as for the two compositions.
AB - Type II clathrates are interesting due to their potential thermoelectric applications. Powdered X-ray diffraction (XRD) data and density functional calculations for NaxSi136 found a lattice contraction as x increases for 0 < x < 8 and an expansion as x increases for x > 8. This is explained by XRD data that shows that as x increases, the Si28 cages are filled first for x < 8 and the Si20 cages are then filled for x > 8. Motivated by this work, here we report the results of first-principles calculations of the structural and vibrational properties of the Type II clathrate compounds AxSi136, AxGe136, and AxSn136. We present results for the variation of the lattice constants, bulk moduli, and other structural parameters with x. These are contrasted for the Si, Ge, and Sn compounds and for guests A = Na, K, Rb, and Cs. We also present calculated results of phonon dispersion relations for Na4Si136, Na4Ge136, and Na4Sn136 and we compare these for the three materials. Finally, we present calculated results for the elastic constants in NaxSi136, NaxGe136, and NaxSn136 for x = 4 and 8. These are compared for the three hosts, as well as for the two compositions.
KW - Alkali atoms
KW - Clathrates
KW - Elastic constants
KW - First principles theory
KW - Group 14
KW - Guests
KW - Phonon
KW - Type II-structure
KW - VASP
UR - http://www.scopus.com/inward/record.url?scp=84984620281&partnerID=8YFLogxK
U2 - 10.3390/ma9080691
DO - 10.3390/ma9080691
M3 - Article
AN - SCOPUS:84984620281
SN - 1996-1944
VL - 9
JO - Materials
JF - Materials
IS - 8
M1 - 691
ER -