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RISS 인기검색어
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- 저자 : Lydia Rathnam (검색결과 3 건)
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Thermoelectric properties in Fermi level tuned topological materials (Bi1−xSnx)2Te3
Chan‑Chieh Lin,손원혁,Lydia Rathnam,이종수 대한금속·재료학회 2018 ELECTRONIC MATERIALS LETTERS Vol.14 No.2
We investigated the thermoelectric properties of Sn-doped (Bi1−xSnx)2Te3 (x = 0, 0.1, 0.3, 0.5, and 0.7%) compounds,which is known as topological insulators. Fermi level tuning by Sn-doping can be justified by the n- to p-type transitionwith increasing Sn-doping concentration, as confirmed by Seebeck coefficient and Hall coefficient. Near x = 0.3 and 0.5%,the Fermi level resides inside the bulk band gap, resulting in a low Seebeck coefficient and increase of electrical resistivity. The magnetoconductivity with applying magnetic field showed weak antilocalization (WAL) effect for pristine Bi2Te3while Sn-doped compounds do not follow the WAL behavior of magneto-conductivity, implying that the topological surfaceDirac band contribution in magneto-conductivity is suppressed with decreasing the Fermi level by Sn-doping. This researchcan be applied to the topological composite of p-type/n-type topological materials by Fermi level tuning via Sn-doping inBi2Te3compounds.
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Ginting, Dianta,Lin, Chan-Chieh,Rathnam, Lydia,Yun, Jae Hyun,Yu, Byung-Kyu,Kim, Sung-Jin,Rhyee, Jong-Soo Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.26
<P>In a composite of two dissimilar or homologous semiconductors with different energy band gaps or metal/semiconductor composites, we expect a band bending effect at the interfaces. The band bending effect induced by the different Fermi levels of two compounds can selectively scatter carriers due to energy-dependent scattering time, resulting in enhancement of the Seebeck coefficient. In addition, nano-inclusions in a matrix will effectively scatter phonons. Here, we demonstrate the effects of electron and phonon scattering by nano-inclusions in n-type (PbTe0.93−xSe0.07Clx)0.93(PbS)0.07(<I>x</I>= 0.0005, 0.01, 0.1 and 0.2) composites. In the matrix, the nano-inclusions increased the Seebeck coefficient while reducing lattice thermal conductivity in (PbTe0.93−xSe0.07Clx)0.93(PbS)0.07. The chlorine doping increases the Fermi level to the bottom of the conduction band giving rise to increased electron concentration. The simultaneous emergence of the high Seebeck coefficient and low thermal conductivity resulted in the exceptional<I>ZT</I>value of 1.52 at 700 K for low chlorine doping (<I>x</I>= 0.0005), which is a very high value in n-type thermoelectric materials. The randomly distributed interface potential, induced by Fermi level tuning, with nano-inclusions is a new criterion for investigating thermoelectric properties.</P>
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Ginting, Dianta,Lin, Chan-Chieh,Rathnam, Lydia,Kim, Gareoung,Yun, Jae Hyun,So, Hyeon Seob,Lee, Hosun,Yu, Byung-Kyu,Kim, Sung-Jin,Ahn, Kyunghan,Rhyee, Jong-Soo American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.14
<P>Topological insulators have attracted much interest in topological states of matter featuring unusual electrical conduction behaviors. It has been recently reported that a topological crystalline insulator could exhibit a high thermoelectric performance by breaking its crystal symmetry via chemical doping. Here, we investigate the multiple effects of Na, Se, and S alloying on thermoelectric properties of a topological crystalline insulator Pb<SUB>0.6</SUB>Sn<SUB>0.4</SUB>Te. The Na doping is known to be effective for breaking the crystalline mirror symmetry of Pb<SUB>0.6</SUB>Sn<SUB>0.4</SUB>Te. We demonstrate that simultaneous emergence of band convergence by Se alloying and nanostructuring by S doping enhance the power factor and decrease lattice thermal conductivity, respectively. Remarkably, the high power factor of 22.3 μW cm<SUP>-1</SUP> K<SUP>-2</SUP> at 800 K is achieved for Na 1%-doped Pb<SUB>0.6</SUB>Sn<SUB>0.4</SUB>Te<SUB>0.90</SUB>Se<SUB>0.05</SUB>S<SUB>0.05</SUB> mainly due to a relatively high Seebeck coefficient via band convergence by Se alloying as well as the suppression of bipolar conduction at high temperatures by the increase of energy band gap. Furthermore, the lattice thermal conductivity is significantly suppressed by PbS nanoprecipitates without deteriorating the hole carrier mobility, ranging from 0.80 W m<SUP>-1</SUP> K<SUP>-1</SUP> for Pb<SUB>0.6</SUB>Sn<SUB>0.4</SUB>Te to 0.17 W m<SUP>-1</SUP> K<SUP>-1</SUP> at 300 K for Pb<SUB>0.6</SUB>Sn<SUB>0.4</SUB>Te<SUB>0.85</SUB>Se<SUB>0.10</SUB>S<SUB>0.05</SUB>. As a result, the synergistically combined effects of breaking the crystalline mirror symmetry of topological crystalline insulator, band convergence, and nanostructuring for Pb<SUB>0.6</SUB>Sn<SUB>0.4</SUB>Te<SUB>0.95-<I>x</I></SUB>Se<SUB><I>x</I></SUB>S<SUB>0.05</SUB> (<I>x</I> = 0, 0.05, 0.1, 0.2, and 0.95) give rise to an impressively high <I>ZT</I> of 1.59 at 800 K for <I>x</I> = 0.05. We suggest that the multiple doping in topological crystalline insulators is effective for improving the thermoelectric performance.</P> [FIG OMISSION]</BR>
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