Thermal transport and Inelastic Neutron Scattering on Sb doped GeTe Crystals

Min Nan Ou^1*, Shin-ichiro Yano², Tian-Wei Lan¹, V.K.Ranganayakulu^1,3, Shih Hsun Yu^1,4, Tsu-Lien Hung¹, Yang-Yuan Chen¹

¹Institute of Physics, Academia Sinica, Taipei City, Taiwan
²National Synchrotron Radiation Research Center, Hsinchu, Taiwan
³Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan
⁴Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung, Taiwan

* Presenter:Min Nan Ou, email:oumn@gate.sinica.edu.tw

The performance of thermoelectric materials evaluated by the dimensionless figure of merit zT. The factor z is defined as z ≡ S²/ρκ=F_P/(κ_ph+κ_e), where the S, ρ, κ_ph, κ_e, and F_P are Seebeck coefficient, resistivity, phonon and electron thermal conductivity, and power factor, respectively. In past decades, most work to increase zT in thermoelectric materials has made by reducing κ_ph while preserving their electrical properties. Therefore, the understanding of dynamic properties on phonon propagation may provide more information for the further reduction of thermal conductivity. The neutron inelastic scattering techniques provide an opportunity for overall understanding of phonon dynamics in a whole crystal sample. In usual, GeTe is regarding as a high F_P but less efficient thermoelectric material because of its high thermal conductivity. A strategy for zT enhancing is to reduce thermal conductivity to improve the figure of merit by chemical doping; some successful examples are Pb and Sb dopants. Among them, the Sb dopant considered as a great candidate due to its environment friendly. In this work, an optimized dopant of x=0.08 is employed to increases power factor slightly and to suppresses thermal conductivity significantly. The Sb doped GeTe crystals were synthesized by means of Bridgman method. Their crystal structure and texture details investigated by powder and single crystal XRD. With the inelastic neutron scattering investigation with SIKA, phonon dispersion relation (PDR) measured on two selected GeTe and Ge0.92Sb0.08Te crystals for both Γ to A and Γto M directions. We identified that the phonon dispersion modified obviously by chemical doping.

Keywords: Thermoelectricity, crystal, Phonon, neutron inelastic scattering