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

Chan-Chieh Lin,Dianta Ginting,김가령,안경한,이종수 한국물리학회 2018 Current Applied Physics Vol.18 No.12

SnSe single crystal showed a high thermoelectric zT of 2.6 at 923 K mainly due to an extremely low thermal conductivity 0.23Wm−1 K−1. 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 KxSn1−xSe (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 Kdoping 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 K0.001Sn0.999Se sample shows an exceptionally high zT of 1.11 at 823 K which is significantly enhanced value in polycrystalline compounds.

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.

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>

Extremely Low Lattice Thermal Conductivity and Point Defect Scattering of Phonons in Ag-doped (SnSe)_1–<i>x</i>(SnS)_<i>x</i> Compounds

Lin, Chan-Chieh,Lydia, R.,Yun, Jae Hyun,Lee, Ho Seong,Rhyee, Jong Soo American Chemical Society 2017 Chemistry of materials Vol.29 No.12

<P>Single crystalline SnSe has been reported to exhibit the high thermoelectric zT value of 2.6 at 923 K along the b-axis direction, due to its low thermal conductivity [Zhao, L. D.; et al. Nature 2014, 508, 373]. However, the strongly anisotropic properties of the orthorhombic structure degrade the thermoelectric performance of polycrystalline SnSe, resulting in a low zT of 0.6 and 0.8 for Ag- and Na-doped SnSe, respectively. Here, we prepared Ag0.01Sn0.99Se1-xSx (x = 0, 0.10, 0.15, 0.20, and 0.35) compounds by melting and hot press sintering. The compounds showed extremely low thermal conductivity (0.11 W m(-1) K-1 at 825 K for x = 0.15). Using transmission electron microscopy images, we found that SnS alloying induced numerous nanoscale point defects. A Debye-Callaway model analysis supported the conclusion that the extremely low lattice thermal conductivity could be attributed to the point defect scattering of phonons. This resulted in a high zT of 1.67 at 823 K for the x = 0.15 sample, which is the state-of-the-art zT value for polycrystalline SnSe. Because the compounds are based on the environmentally friendly and cheap materials Sn, Se, and S, they make promising candidates for thermoelectric applications.</P>

Carbon induced phase transformation in electrospun TiO₂/multiwall carbon nanotube nanofibers

Tsai, Chieh-Ming,Song, Chan-Geun,Hung, Yung-Chieh,Jeong, Yong-Gi,Oh, Sung Hoon,Jeong, Joong Hoon,Kim, Huijin,Huh, Hoon,Yoon, Jong-Won,Sigmund, Wolfgang Elsevier 2017 CERAMICS INTERNATIONAL Vol.43 No.4

<P><B>Abstract</B></P> <P>Nanofibers of titania and composite nanofibers of titania and multiwall carbon nanotubes were synthesized by electrospinning using a sol-gel process combined with activated carbon nanotubes. The relationships of treatment temperature, carbon nanotube content on the crystal phase, fiber morphology, and electric properties are reported. It is found that the rutile phase becomes more prominent at low heat treatment temperatures with an increase of carbon content in nanofibers, be it for higher amount of carbon due to reducing atmosphere or due to an increase in MWCNT. Atmospheric control and lower heat treatment temperatures enable crystalline nanocomposite fibers of anatase where the level of rutile is below the detection limit of XRD or Raman spectroscopy. This work provides a new path to fabricate electrospun TiO<SUB>2</SUB>/MWCNT nanocomposite nanofibers with limited C-induced rutile phase.</P>

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>

Development of multispectral imaging algorithm for detection of frass on mature red tomatoes

Yang, Chun-Chieh,Kim, Moon S.,Millner, Patricia,Chao, Kuanglin,Cho, Byoung-Kwan,Mo, Changyeun,Lee, Hoyoung,Chan, Diane E. Elsevier 2014 Postharvest biology and technology Vol.93 No.-

In this research, a multispectral fluorescence-based imaging algorithm was developed to detect frass contamination on mature Campari tomatoes. Tomato images were acquired using a hyperspectral fluorescence line-scan imaging system with violet LED excitation, then analyzed for wavelength selection. The fluorescence intensities at five wavelengths, 515 nm, 640 nm, 664 nm, 690 nm, and 724 nm, were used to compute three simple ratio functions to detect frass contamination. The contamination spots were created on the tomato surfaces using four low-concentration frass dilutions. The algorithms detected over 99% of the 0.2 kg/L and 0.1 kg/L frass contamination spots and successfully differentiated these spots from tomato skin surfaces, stem scars, and stems. However, differentiation of the 0.05 kg/L and 0.02 kg/L frass contamination spots was more difficult. Adjusting the algorithm to successfully detect 95% of the 0.05 kg/L spots also resulted in false-positive pixel detections occurring on 28% of the tomatoes. This study demonstrates that a simple multispectral fluorescence imaging algorithm based on violet LED excitation could be useful for rapid postharvest detection of frass contamination on tomatoes in processing lines. (C) 2014 Published by Elsevier B.V.

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.

Prognostic value of right pulmonary artery distensibility in dogs with pulmonary hypertension

I-Ping Chan,Min-Chieh Weng,Tung Hsueh,Yun-Chang Lin,Shiun-Long Lin 대한수의학회 2019 Journal of Veterinary Science Vol.20 No.4

The right pulmonary artery distensibility (RPAD) index has been used in dogs with pulmonary hypertension (PH) caused by heartworm infection, myxomatous mitral valve disease, or patent ductus arteriosus. We hypothesized that this index correlates with the tricuspid regurgitation pressure gradient (TRPG) assessed by echocardiography and could predict survival in dogs with PH secondary to various causes. To assess this hypothesis, the medical records of 200 client-owned dogs at a referral institution were retrospectively reviewed. The RPAD index and the ratios of acceleration time to peak pulmonary artery flow (AT) and to the ejection time of pulmonary artery flow (ET) were recorded for each dog. The owners were contacted for follow-up assessments. The findings indicated that the RPAD index was correlated with the TRPG (R2 = 0. 362, p < 0.001). The survival time was significantly shorter in dogs with an RPAD index ≤ 21% that were followed up for 3 months and in dogs with an RPAD index ≤ 24% that were followed up for 1 year. Thus, the RPAD index was correlated with the TRPG and could predict the clinical outcome in dogs with PH caused by various diseases. This index could be used to evaluate the severity of PH in dogs without tricuspid regurgitation.

High thermoelectric performance in pseudo quaternary compounds of (PbTe)_0.95−x(PbSe)_x(PbS)_0.05 by simultaneous band convergence and nano precipitation

Ginting, Dianta,Lin, Chan-Chieh,Lydia, R.,So, Hyeon Seob,Lee, Hosun,Hwang, Junpil,Kim, Woochul,Al Rahal Al Orabi, Rabih,Rhyee, Jong-Soo Elsevier 2017 Acta materialia Vol.131 No.-

<P>Lead chalcogenides have long been studied as promising thermoelectric materials, operating at the mid temperature range of 500-950 K. Here, we studied thermoelectric properties of pseudo-quaternary compounds of (PbTe)(0.95-x)(PbSe)(x)(PbS)(0.05) (x = 0.0, 0.05, 0.10, 0.15, 0.20, 035, and 0.95) with 1% Nadoping, synthesized by melting and rapid quenching of pristine compounds of PbTe, PbSe, and PbS and followed by hot press sintering. The lattice parameters and transmission electron microscopy confirmed that the PbSe makes solid solution with PbTe leading to PbTe1-xSex matrix while the PbS precipitates in the matrix. In terms of two valence bands model, the energy band gap between conduction and valence L-band was decreased and the energy difference between L-and E-bands was increased with increasing Se concentration. The band convergence at high temperature may be associated with the enhancement of power factor. The PbS nano-scale precipitation in the matrix attributed to the decrease of lattice thermal conductivity. From the Matthiessen's rule, the lattice thermal conductivity was described by the nano precipitation as well as alloy scattering of phonons. The simultaneous emergence of band convergence and nano-precipitation in the quaternary compounds of (PbTe)(0.95-X)(PbSe)(x)(PbS)(0.05) gives rise to exceptionally high zT value of 23 at 800 K for x = 0.20. The high zT value also showed enhancement of practical thermoelectric performances such as engineering zT(eng), device efficiency eta, output power density P-d, and device zT(d). In addition, high zT compounds have good compatibility with the n-type I-doped PbTe compound, which can be applied to practical waste heat power generation. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.</P>