Influence of Te Vacancies on the Thermoelectric Properties of n-type Cu0.008Bi2Te2.7-xSe0.3

In this study, we report the influence of Te vacancy formation on the thermoelectric properties of n-type Cu0.008Bi2Te2.7Se0.3 alloys, including their electronic and thermal transport properties. Te-deficient Cu0.008Bi2Te2.7-xSe0.3 (x = 0, 0.005, 0.01 and 0.02) samples were systematically synthesized and characterized. Regarding electronic transport properties, carrier concentration was increased with Te vacancies, while carrier mobility was maintained. As a result, the electrical conductivity significantly increased while the Seebeck coefficient reduced moderately, thus, the power factor was enhanced from 3.04 mW/mK (pristine) to 3.22 mW/mK (x = 0.02) at 300 K. Further analysis based on a single parabolic band model revealed that the weighted mobility of the conduction band increased, which is favorable for electron transport, as Te vacancies were generated. Regarding thermal transport properties, lattice thermal conductivity decreased with Te vacancies due to additional point defect phonon scattering, however, total thermal conductivity increased due to larger electronic contribution as Te vacancies increased. Analysis using the Debye-Callaway model suggests that the phonon scattering by the Te vacancies is as efficient as the substitution point defect scattering. Consequently, the thermoelectric figure of merit zT increased at all temperatures for x = 0.005 and 0.01. The maximum zT of 0.95 was achieved for Te-deficient Cu0.008Bi2Te2.69Se0.3 (x = 0.01) at 400 K. (Received August 11, 2020; Accepted August 20, 2020)

[1]  Yuedong Yu,et al.  Enhanced Electrical Transport Properties via Defect Control for Screen-Printed Bi2Te3 Films over a Wide Temperature Range. , 2020, ACS applied materials & interfaces.

[2]  W. Shin,et al.  Reduced Bipolar Conduction in Bandgap-Engineered n-Type Cu0.008Bi2(Te,Se)3 by Sulfur Doping , 2020 .

[3]  Hyun Sik Kim,et al.  Effect of Cu/In Doping on the Thermoelectric Transport Properties of Bi-Sb-Te Alloys , 2019, Korean Journal of Metals and Materials.

[4]  Kyu Hyoung Lee,et al.  Clarification of electronic and thermal transport properties of Pb-, Ag-, and Cu-doped p-type Bi0.52Sb1.48Te3 , 2019, Journal of Alloys and Compounds.

[5]  X. Qin,et al.  High thermoelectric performance of n-type Bi2Te2.7Se0.3via nanostructure engineering , 2018 .

[6]  W. Shin,et al.  Suppression of bipolar conduction via bandgap engineering for enhanced thermoelectric performance of p-type Bi0.4Sb1.6Te3 alloys , 2018 .

[7]  Xinbing Zhao,et al.  Thermoelectric performance of p-type zone-melted Se-doped Bi0.5Sb1.5Te3 alloys , 2018, Rare Metals.

[8]  W. Jung,et al.  Thermoelectric Properties of Cu-doped Bi2−xSbxTe3 Prepared by Encapsulated Melting and Hot Pressing , 2018, Metals and Materials International.

[9]  Haijun Wu,et al.  Enhancing Thermoelectric Performance of n-Type Hot Deformed Bismuth-Telluride-Based Solid Solutions by Nonstoichiometry-Mediated Intrinsic Point Defects. , 2017, ACS applied materials & interfaces.

[10]  G. J. Snyder,et al.  Phonon scattering by dislocations at grain boundaries in polycrystalline Bi0.5Sb1.5Te3 , 2017 .

[11]  D. Rowe.  Materials, preparation, and characterization in thermoelectrics , 2016 .

[12]  G. J. Snyder,et al.  Dense dislocation arrays embedded in grain boundaries for high-performance bulk thermoelectrics , 2015, Science.

[13]  G. J. Snyder,et al.  Characterization of Lorenz number with Seebeck coefficient measurement , 2015 .

[14]  G. J. Snyder,et al.  Band gap estimation from temperature dependent Seebeck measurement - Deviations from the 2e|S|maxTmax relation , 2015 .

[15]  Soon-Mok Choi,et al.  Thermoelectric properties of Cu-dispersed bi0.5sb1.5te3 , 2012, Nanoscale Research Letters.

[16]  G. J. Snyder,et al.  Complex thermoelectric materials. , 2008, Nature materials.

[17]  M. Stordeur,et al.  The Thermoelectric Figure of Merit in the Mixed Crystal System p‐(Bi1−xSbx)2 Te3 , 1990 .

[18]  Kyu Hyoung Lee,et al.  Recent progress in Bi-Te-based thermoelectric materials , 2015 .