Dynamics of the crystal structure of tin-based type-I clathrates with different degrees of disorder in their cationic frameworks

The temperature dependencies of heat capacity, C P ( T ), and cubic unit cell parameter, a ( T ), were experimentally obtained in the range of 2-300 K for the compounds Sn 24 P 19.2 I 8 , Sn 20 Zn 4 P 20.8 I 8 , and Sn 17 Zn 7 P 22 I 8 , which belong to a family of type-I clathrates. The experimenta...

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Published in:Physical chemistry chemical physics : PCCP 2017-10, Vol.19 (4), p.27725-2773
Main Authors: Novikov, V. V, Pilipenko, K. S, Matovnikov, A. V, Mitroshenkov, N. V, Kornev, B. I, Likhanov, M. S, Tyablikov, A. S, Shevelkov, A. V
Format: Article
Language:English
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Summary:The temperature dependencies of heat capacity, C P ( T ), and cubic unit cell parameter, a ( T ), were experimentally obtained in the range of 2-300 K for the compounds Sn 24 P 19.2 I 8 , Sn 20 Zn 4 P 20.8 I 8 , and Sn 17 Zn 7 P 22 I 8 , which belong to a family of type-I clathrates. The experimental data were analyzed in the frames of the Debye-Einstein approximation, further accounting for the contributions of positional disorder in the clathrate frameworks as well as those of defect modes arising from the distribution of guest atoms over unequal in energy but close in space positions inside the framework cages. By fitting the experimental data, the Debye and Einstein characteristic temperatures describing the dynamics of the framework and guest atoms, respectively, were obtained. Their analysis revealed peculiar dependencies of the characteristic temperatures upon the number of substituted zinc atoms and the concentration of vacancies in the framework, which are discussed in this paper. The temperature dependencies of heat capacity and cubic unit cell parameter for type-I clathrates were obtained to determine the influence of the concentration of vacancies and substituting atoms on the lattice dynamics.
ISSN:1463-9076
1463-9084
DOI:10.1039/c7cp05023b