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Materials 2016, 9(8), 616; doi:10.3390/ma9080616

Lattice Dynamics Study of Phonon Instability and Thermal Properties of Type-I Clathrate K8Si46 under High Pressure

1
School of Science, Southwest University of Science and Technology, Mianyang 610064, Sichuan, China
2
College of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 400047, China
3
State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Southwest University of Science and Technology, Mianyang 610064, Sichuan, China
4
Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, Chinese Academy of Engineering Physics, Mianyang 621900, Sichuan, China
*
Author to whom correspondence should be addressed.
Academic Editors: Matt Beekman and Yuri Grin
Received: 15 June 2016 / Revised: 11 July 2016 / Accepted: 21 July 2016 / Published: 25 July 2016
(This article belongs to the Special Issue Inorganic Clathrate Materials)
View Full-Text   |   Download PDF [8005 KB, uploaded 25 July 2016]   |  

Abstract

For a further understanding of the phase transitions mechanism in type-I silicon clathrates K8Si46, ab initio self-consistent electronic calculations combined with linear-response method have been performed to investigate the vibrational properties of alkali metal K atoms encapsulated type-I silicon-clathrate under pressure within the framework of density functional perturbation theory. Our lattice dynamics simulation results showed that the pressure induced phase transition of K8Si46 was believed to be driven by the phonon instability of the calthrate lattice. Analysis of the evolution of the partial phonon density of state with pressure, a legible dynamic picture for both guest K atoms and host lattice, was given. In addition, based on phonon calculations and combined with quasi-harmonic approximation, the specific heat of K8Si46 was derived, which agreed very well with experimental results. Also, other important thermal properties including the thermal expansion coefficients and Grüneisen parameters of K8Si46 under different temperature and pressure were also predicted. View Full-Text
Keywords: phonon spectrum; clathrate compounds; lattice dynamics; high pressure phonon spectrum; clathrate compounds; lattice dynamics; high pressure
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Zhang, W.; Zeng, Z.Y.; Ge, N.N.; Li, Z.G. Lattice Dynamics Study of Phonon Instability and Thermal Properties of Type-I Clathrate K8Si46 under High Pressure. Materials 2016, 9, 616.

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