Phase stability and lattice thermal conductivity reduction in CoSb3 skutterudites, doped with chalcogen atoms

M Battabyal,L Pradipkanti,Dillip K Satapathy,B Priyadarshini,R Gopalan

doi:10.1063/1.4959102

Abstract

We report a significant reduction in the lattice thermal conductivity of the CoSb3 skuttertudites, doped with chalcogen atoms. Te/Se chalcogen atoms doped CoSb3 skutterudite samples (Te0.1Co4Sb12, Se0.1Co4Sb12, Te0.05Se0.05Co4Sb12) are processed by ball milling and spark plasma sintering. X-ray diffraction data combined with energy dispersive X-ray spectra indicate the doping of Te/Se chalcogen atoms in the skutterudite. The temperature dependent X-ray diffraction confirms the stability of the Te/Se doped CoSb3 skutterudite phase and absence of any secondary phase in the temperature range starting from 300 K to 773 K. The Raman spectroscopy reveals that different chalcogen dopant atoms cause different resonant optical vibrational modes between the dopant atom and the host CoSb3 skutterudite lattice. These optical vibrational modes do scatter heat carrying acoustic phonons in a different spectral range. It was found that among the Te/Se chalcogen atoms, Te atoms alter the host CoSb3 skutterudite lattice vibrations to a larger extent than Se atoms, and can potentially scatter more Sb related acoustic phonons. The Debye model of lattice thermal conductivity confirms that the resonant phonon scattering has important contributions to the reduction of lattice thermal conductivity in CoSb3 skutterudites doped with Te/Se chalcogen atoms. Lattice thermal conductivity ∼ 0.9 W/mK at 773 K is achieved in Te0.1Co4Sb12 skutterudites, which is the lowest value reported so far in CoSb3 skutterudites, doped with single Te chalcogen atom.

Highlights

Chemical substitution and cage filling of the CoSb3 skutterudites draw enormous attention in the last two decades due to their enhanced thermoelectric properties in the intermediate temperature range starting from 600 K to 800 K.1–3 Skutterudites have cubic structures with space group Im3 ̄
X-ray energy dispersive spectroscopy (EDS) mapping combined with the scanning electron microscope (SEM) of Te0.1 sample is shown in Fig. 1, which confirms that Co, Sb and Te are distributed uniformly throughout the surface of Te0.1 sample
X-ray diffraction data combined with energy dispersive X-ray spectroscopy confirm that in all the cases, Te/Se chalcogen atoms are being doped to the skutterudite lattice and the elements are distributed homogeneously throughout the sample

Summary

Introduction

Chemical substitution and cage filling of the CoSb3 skutterudites draw enormous attention in the last two decades due to their enhanced thermoelectric properties in the intermediate temperature range starting from 600 K to 800 K.1–3 Skutterudites have cubic structures with space group Im3 ̄. Chemical substitution and cage filling of the CoSb3 skutterudites draw enormous attention in the last two decades due to their enhanced thermoelectric properties in the intermediate temperature range starting from 600 K to 800 K.1–3. As proposed by Slack, phonon-glass-electron-crystal model in skutterudites can be achieved by partial or complete filling of these cages with the filling atoms, called as fillers. Fillers act as “rattlers” to enhance the phonon scattering and reduce the thermal conductivity (k).[4,5,6,7,8] Reducing the thermal conductivity is the important factor for thermoelectric materials, because it enhances the figure of merit (ZT), which is represented by ZT=S2T/ρk. It is known that in a semiconductor like CoSb3 skutterudites, k is the combined effect of electronic thermal conductivity (ke) and lattice thermal conductivity (kL). The fillers provide an additional phonon scattering channel known as resonant scattering, which enhances

Methods

Results

Conclusion