Experimental determination of phonon thermal conductivity and Lorenz ratio of single-crystal bismuth telluride
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Research Letter
Experimental determination of phonon thermal conductivity and Lorenz ratio of single-crystal bismuth telluride Mengliang Yao and Cyril Opeil, Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, USA Stephen Wilson, Materials Department, University of California, Santa Barbara, California 93106, USA Mona Zebarjadi, Department of Electrical and Computer Engineering and Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904, USA Address all correspondence to Cyril Opeil at [email protected] (Received 2 August 2017; accepted 11 October 2017)
Abstract We use a magnetothermal resistance method to measure the lattice thermal conductivity of single-crystal Bi2Te3 from 5 to 60 K. Lattice thermal conductivity is calculated by extrapolating the thermal conductivity versus electrical conductivity curve to a zero electrical conductivity value. Our results show that the measured phonon thermal conductivity follows the eDmin /T temperature dependence and the Lorenz ratio corresponds to the modified Sommerfeld value in the intermediate temperature range. Our low-temperature experimental data and analysis on Bi2Te3 are a complement to previous measurements of Goldsmid (Ref. 17) and theoretical calculations by Hellman et al. (Ref. 18) at higher temperature 100–300 K.
Introduction For most materials at low temperatures their thermal transport κtot involves two types of carriers: one (κe) is the electron (or hole) contribution, which conducts both charge and heat, and the other (κph) is the phonon (or equivalently lattice) contribution, which only conducts heat; normally it is not easy to separate κe or κph from κtot.[1–3] In our previous work, we successfully applied the magnetothermal resistance (MTR) method to three different single crystal metals (Al, Cu, and Zn) by suppressing κe in a strong magnetic field and extracted κph from the extrapolation.[4] Unlike metals, which reveal an electron dominant thermal transport (κe ≫ κph), semiconductors and semimetals are completely different where these two components are comparable (kph ke ) or even phonon dominant (κph > κe).[3,5] As a result, it is germane to verify the MTR method on materials other than metals, such as single-crystal semiconductors, in the same temperature range, of which the thermal transport are usually phonon dominant. Today, many thermoelectric (TE) materials utilize a nanocomposite structure and are nearly impossible to model using fully first-principles calculation approaches because of their nearly random matrix structure. Here we explore a single-crystal of Bi2Te3 in order to encourage theoretical modeling of this and other TE materials. Using our method, we can extract lattice thermal conductivity as opposed to total thermal conductivity,[4] and our results could be directly compared with first-principles calculations. When applying the MTR method, there are several important quantities for describing the transport process. The deflecting angle γ is defined as the deviation of an
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