Anomalous thermoelectric power and polaronic transport in the vicinity of topological phase transition of Pb_1-xSn_xTe

Kim, Gareoung,Yun, Jae Hyun,Rhyee, Jong-Soo Elsevier 2019 The Journal of physics and chemistry of solids Vol.126 No.-

<P><B>Abstract</B></P> <P>Pb<SUB> <B>1−<I>x</I> </B> </SUB>Sn<SUB> <I>x</I> </SUB>Te compounds exhibits the topological phase transition from trivial semiconductor (PbTe) to topological crystalline insulator (SnTe). In the vicinity of topological phase transition in the region of Pb<SUB> <B>1−<I>x</I> </B> </SUB>Sn<SUB> <I>x</I> </SUB>Te ( x = 0.2, 0.3, and 0.4), the band touching of conduction L 6 − and valence L 6 + bands gives rise to topological Dirac semimetal. Here we investigated thermoelectric properties in the region of topological Dirac semimetal in Pb<SUB> <B>1−<I>x</I> </B> </SUB>Sn<SUB> <I>x</I> </SUB>Te compounds. From the temperature-dependent Hall <SUB> R H </SUB> ( T ) and Seebeck coefficients S ( T ) , we found the abnormal sign difference between Hall (positive <SUB> R H </SUB> ) and Seebeck (negative <I>S</I>) coefficients in the compounds of x = 0.3 and x = 0.4 at intermediate temperature range. We analyzed the abnormal sign difference between the Hall and Seebeck coefficients in terms of the Aharanov-Bohm effect of non-adiabatic 3-site polaron hopping. The polaronic hopping in the compounds can be justified by strong electron-phonon coupling. The temperature-dependent behavior of Hall mobility <SUB> μ H </SUB> ( T ) and carrier density <SUB> n H </SUB> ( T ) indicates the strong electron-phonon scattering. From the temperature-dependent thermal conductivity κ ( T ) measurement, the broad peaks at low temperature, driven by freezing-out of Umklapp scattering, are systematically suppressed by increasing Sn concentration, which consistent with the strong electron-phonon interaction in the system.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We investigated thermoelectric properties in Dirac semimetals Pb<SUB>1-x</SUB>Sn<SUB>x</SUB>Te. </LI> <LI> Abnormal sign difference between Hall and Seebeck coefficients. </LI> <LI> Sign difference in n<SUB>H</SUB> and S is caused by non-adiabatic 3-site polaron hopping. </LI> <LI> Strong electron-phonon coupling in the compounds. </LI> <LI> Umklapp scattering is suppressed by Sn substitution. </LI> </UL> </P>

Texture-induced reduction in electrical resistivity of p-type (Bi,Sb)₂Te₃ by a hot extrusion

Min, Bongki,Lim, Sang-Soon,Jung, Sung-Jin,Kim, Gareoung,Lee, Byeong-Hyeon,Won, Sung Ok,Kim, Seong Keun,Rhyee, Jong-Soo,Kim, Jin-Sang,Baek, Seung-Hyub Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.764 No.-

<P><B>Abstract</B></P> <P>The electrical resistance of a thermoelectric module is an important parameter as well as the thermoelectric figure-of-merit for the application of both waste energy harvesters and solid-state cooling devices. High resistance causes energy dissipation through Joule heating, leading to the degradation of the device's generating or cooling performance. Therefore, it is highly desirable to reduce the electric resistivity of the thermoelectric materials. Here, we report a hot extrusion technique to fabricate p-type bismuth antimony tellurides that has low electrical resistivity. Extrusion is a promising tool to fabricate a fiber-like texture of the microstructure, where the 001 normal vector of grains is pointing perpendicular to the extrusion direction. Such a textured microstructure can enhance the mobility of electrical carriers along the extrusion direction due to the anisotropic nature of electrical transport in bismuth telluride-based alloys. Beyond bismuth telluride-based thermoelectric materials, we believe that our result will offer a simple tool to manipulate physical properties of any two-dimensional, layered materials by controlling microstructure.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A hot extrusion is used to fabricate p-type (Bi,Sb)<SUB>2</SUB>Te<SUB>3</SUB> with a <<I>110</I>> fiber texture. </LI> <LI> Electrical mobility is improved along the extrusion direction. </LI> <LI> Electrical resistivity of the extrudates is lower than that of the SPSed samples. </LI> <LI> The composition-dependent thermoelectric properties of (Bi<SUB>x</SUB>Sb<SUB>2-x</SUB>)Te<SUB>3</SUB> are reported. </LI> </UL> </P>

Enhancement of Thermoelectric Performances in a Topological Crystal Insulator Pb_0.7Sn_0.3Se via Weak Perturbation of the Topological State and Chemical Potential Tuning by Chlorine Doping

Lin, Chan-Chieh,Kim, Gareoung,Ginting, Dianta,Ahn, Kyunghan,Rhyee, Jong-Soo American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.13

<P>Topological insulators generally share commonalities with good thermoelectric (TE) materials because of their narrow band gaps and heavy constituent elements. Here, we propose that a topological crystalline insulator (TCI) could exhibit a high TE performance by breaking its crystalline symmetry and tuning the chemical potential by elemental doping. As a candidate material, we investigate the TE properties of the Cl-doped TCI Pb<SUB>0.7</SUB>Sn<SUB>0.3</SUB>Se. The infrared absorption spectra reveal that the band gap is increased from 0.055 eV for Pb<SUB>0.7</SUB>Sn<SUB>0.3</SUB>Se to 0.075 eV for Pb<SUB>0.7</SUB>Sn<SUB>0.3</SUB>Se<SUB>0.99</SUB>Cl<SUB>0.01</SUB>, confirming that the Cl doping can break the crystalline mirror symmetry of a TCI Pb<SUB>0.7</SUB>Sn<SUB>0.3</SUB>Se and thereby enlarge its bulk electronic band gap. The topological band inversion is confirmed by the extended X-ray absorption fine structure spectroscopy, which shows that the TCI state is weakened in a chlorine <I>x</I> = 0.05-doped compound. The small gap opening and partial linear band dispersion with massless and massive bands may have a high power factor (PF) for high electrical conductivity with an enhancement of the Seebeck coefficient. As a result, Pb<SUB>0.7</SUB>Sn<SUB>0.3</SUB>Se<SUB>0.99</SUB>Cl<SUB>0.01</SUB> shows a considerably enhanced <I>ZT</I> of 0.64 at 823 K, which is about 1200% enhancement in <I>ZT</I> compared with that of the undoped Pb<SUB>0.7</SUB>Sn<SUB>0.3</SUB>Se. This work demonstrates that the optimal n-type Cl doping tunes the chemical potential together with breaking the state of the TCI, suppresses the bipolar conduction at high temperatures, and thereby enables the Seebeck coefficient to increase up to 823 K, resulting in a significantly enhanced PF at high temperatures. In addition, the bipolar contribution to thermal conductivity is effectively suppressed for the Cl-doped samples of Pb<SUB>0.7</SUB>Sn<SUB>0.3</SUB>Se<SUB>1-<I>x</I></SUB>Cl<SUB><I>x</I></SUB> (<I>x</I> ≥ 0.01). We propose that breaking the crystalline mirror symmetry in TCIs could be a new research direction for exploring high-performance TE materials.</P> [FIG OMISSION]</BR>

Enhanced magnetocaloric effect in Eu-doped La0.7Ca0.3MnO3 compounds

N.T. Dang,D.P. Kozlenko,Kim Gareoung,손원혁,이종수,Dimitar N. Petrov,T. V. Manh,Phan The Long 한국물리학회 2020 Current Applied Physics Vol.20 No.6

Orthorhombic La0.7-xEuxCa0.3MnO3 samples (x = 0.04–0.12) with apparent density of ρ = 3.9–4.1 g/cm3 prepared by solid-state reactions have been studied. The analysis of temperature-dependent magnetization for an applied field H = 500 Oe indicated a decrease of the Curie temperature (TC) from about 225 K for x = 0.04 through 189 K for x = 0.08–146 K for x = 0.12. The magnetocaloric (MC) study upon analyzing M(H, T) data has revealed that the magnetic entropy change around TC reaches the maximum (|ΔSmax|), which is dependent on both x and H. For an applied field interval of ΔH = 60 kOe, |ΔSmax| values are about 5.88, 4.93, and 4.71 J/ kg⋅K for x = 0.04, 0.08, and 0.12, respectively. Though |ΔSmax| decreases with increasing x, relative cooling power (RCP) increases remarkably from 383 J/kg for x = 0.04 to about 428 J/kg for x = 0.08 and 0.12. This is related to the widening of the ferromagnetic-paramagnetic transition region when x increases. Particularly, if combining two compounds with x = 0.04 and 0.08 (or 0.12) as refrigerant blocks for MC applications, a cooling device can work in a large temperature range of 145–270 K, corresponding to RCP ≈ 640 J/kg for H = 60 kOe. M(H) analyses around TC have proved x = 0.04 exhibiting the mixture of first- and second-order phase transitions while x = 0.08 and 0.12 exhibit a second-order nature. The obtained results show potential applications of Eu-doped La0.7Ca0.3MnO3 materials for magnetic refrigeration below room temperature.

High thermoelectric performance and low thermal conductivity in K-doped SnSe polycrystalline compounds

Lin, Chan-Chieh,Ginting, Dianta,Kim, Gareoung,Ahn, Kyunghan,Rhyee, Jong-Soo ELSEVIER 2018 CURRENT APPLIED PHYSICS Vol.18 No.12

<P><B>Abstract</B></P> <P>SnSe single crystal showed a high thermoelectric zT of 2.6 at 923 K mainly due to an extremely low thermal conductivity 0.23 W m<SUP>−1</SUP> K<SUP>−1</SUP>. It has anisotropic crystal structure resulting in deterioration of thermoelectric performance in polycrystalline SnSe, providing a low zT of 0.6 and 0.8 for Ag and Na-doped SnSe, respectively. Here, we presented the thermoelectric properties on the K-doped K<SUB>x</SUB>Sn<SUB>1−x</SUB>Se (x = 0, 0.1, 0.3, 0.5, 1.5, and 2.0%) polycrystals, synthesized by a high-temperature melting and hot-press sintering with annealing process. The K-doping in SnSe efficiently enhances the hole carrier concentration without significant degradation of carrier mobility. We find that there exist widespread Se-rich precipitates, inducing strong phonon scattering and thus resulting in a very low thermal conductivity. Due to low thermal conductivity and moderate power factor, the K<SUB>0.001</SUB>Sn<SUB>0.999</SUB>Se sample shows an exceptionally high zT of 1.11 at 823 K which is significantly enhanced value in polycrystalline compounds.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The zT value of polycrystalline SnSe remains relatively low value. </LI> <LI> K-doping in SnSe efficiently enhances the hole carrier concentration. </LI> <LI> There exist prevalent Se-rich precipitates in the SnSe matrix, resulting in a very low thermal conductivity. </LI> <LI> The K<SUB>0.001</SUB>Sn<SUB>0.999</SUB>Se sample shows an exceptionally high zT of 1.11 at 823 K. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Temperature-dependent thermal conductivity <I>κ</I> (a) and dimensionless figure-of-merit <I>zT</I> values for K<SUB>x</SUB>Sn<SUB>1-x</SUB>Se (x = 0.0, 0.1, 0.3, 0.5, 1.5, and 2.0 mol.%) compounds.</P> <P>[DISPLAY OMISSION]</P>

Enhancement of Thermoelectric Performance in Na-Doped Pb_0.6Sn_0.4Te_{0.95-<i>x</i>}Se_<i>x</i>S_0.05 via Breaking the Inversion Symmetry, Band Convergence, and Nanostructuring by Multiple Elements Doping

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>

Enhancement of thermoelectric performance <i>via</i> weak disordering of topological crystalline insulators and band convergence by Se alloying in Pb_0.5Sn_0.5Te_{1 − x}Se_x

Ginting, Dianta,Lin, Chan-Chieh,Kim, Gareoung,Yun, Jae Hyun,Yu, Byung-Kyu,Kim, Sung-Jin,Ahn, Kyunghan,Rhyee, Jong-Soo The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.14

<P>Topological crystal insulators (TCIs) that have an even number of topologically protected Dirac bands driven by crystalline mirror symmetry have attracted much attention in condensed matter physics. Here, we demonstrate that a weak disordering in the topological crystalline state can enhance thermoelectric performance significantly due to highly dispersive band dispersion and high band degeneracy which guarantee high electrical mobility and a high Seebeck coefficient, respectively. When we perturb a crystalline mirror symmetry by Se-doping in TCI Pb0.5Sn0.5Te1 − xSex, the topological state becomes weak so that it eventually evolves the normal state. We experimentally prove the topological phase transition concerning Se concentration by X-ray Absorption Spectroscopy (XAS) and extended X-ray absorption Fine Structure (EXAFS) analysis. Small crystalline perturbation by Se doping (<I>x</I> = 0.05) significantly enhances thermoelectric performance due to the simultaneous enhancement of electrical conductivity and the Seebeck coefficient. Therefore, we report an exceptionally high <I>ZT</I> value of 1.9 at 800 K for the <I>x</I> = 0.05 compound which is a 313% enhancement of <I>ZT</I> compared with the pristine compound. This research proposes a new strategy for exploring high-performance thermoelectric materials by weak disordering of topological crystalline Dirac semimetals.</P>

Thermoelectric Properties and Chemical Potential Tuning by K- and Se-Coalloying in (Pb0.5Sn0.5)1-xKxTe0.95Se0.05

Dianta Ginting,Chan-Chieh Lin,Gareoung Kim,Song Yi Back,Bora Won,조현용,Jae Hyun Yun,Hyeon Seob So,Hosun Lee,Byung-Kyu Yu,Sung-Jin Kim,Jong-Soo Rhyee 대한금속·재료학회 2019 ELECTRONIC MATERIALS LETTERS Vol.15 No.3

Topological crystal insulator (TCI) and topological Dirac semimetals have topologically nontrivial surface and bulk state,respectively. The parent compound of Pb 0.5 Sn 0.5 Te exhibiting TCI band inversion has particle-hole symmetry owing to thegapless Dirac band implying a strong electron–hole bipolar compensation in Seebeck coeffi cient. We recently reported thatweak perturbation of TCI state can enhance thermoelectric performance signifi cantly due to highly dispersive and degeneratedenergy bands. It is a great interest that the further increase of chemical potential has benefi ciary to thermoelectric performancein the vicinity of topological phase transition. Here we investigate the thermoelectric properties of the co-doping eff ect by Kand Se in (Pb 0.5 Sn 0.5 ) 1− x K x Te 0.95 Se 0.05 ( x = 0.0, 0.005, 0.010, 0.015, 0.02) compounds. K-doping increases the band gap from0.15 eV (Pb 0.5 Sn 0.5 Te) to 0.21 eV ( x = 0.05) as well as increasing chemical potential resulting in the suppression of bipolardiff usion eff ect. In spite of the suppression of bipolar diff usion eff ect by K-doping, the power factor in K-doped compoundis decreased signifi cantly than the one of non-doped Pb 0.5 Sn 0.5 Te 0.95 Se 0.05 compound. It indicates that when we increasechemical potential further on the breaking of topological band inversion, the thermoelectric performance is deterioratedbecause the chemical potential resides far from the linear band dispersions which become conventional material. The ZTfor the K-doped (Pb 0.5 Sn 0.5 ) 1− x K x Te 0.95 Se 0.05 is obtained as 0.91 at 750 K for x = 0.017 which is increased as much as 99%comparing to the pristine compound Pb 0.5 Sn 0.5 Te but it is reduced value (51.5%) comparing to those of Pb 0.5 Sn 0.5 Te 0.95 Se 0.05compound. We believe that this research is valuable on the confi rmation that the weak perturbation of topological state andappropriate chemical potential tuning are important criteria in high thermoelectric performance.

Quantum critical nature of the short-range magnetic order in Sr2−xLaxIrO4

Rodan, Steven T.,Yoon, Sungwon,Lee, Suheon,Choi, Kwang-Yong,Kim, Gareoung,Rhyee, Jong-Soo,Koda, Akihiro,Chen, Wei-Tin,Chou, Fangcheng American Physical Society 2018 Physical review. B Vol.98 No.21