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Kim, Ki Sung,Kim, Young-Min,Mun, Hyeona,Kim, Jisoo,Park, Jucheol,Borisevich, Albina Y.,Lee, Kyu Hyoung,Kim, Sung Wng Wiley (John WileySons) 2017 Advanced Materials Vol.29 No.36
<P>Structural defects often dominate the electronic- and thermal-transport properties of thermoelectric (TE) materials and are thus a central ingredient for improving their performance. However, understanding the relationship between TE performance and the disordered atomic defects that are generally inherent in nanostructured alloys remains a challenge. Herein, the use of scanning transmission electron microscopy to visualize atomic defects directly is described and disordered atomic-scale defects are demonstrated to be responsible for the enhancement of TE performance in nanostructured Ti1-xHfxNiSn1-ySby half-Heusler alloys. The disordered defects at all atomic sites induce a local composition fluctuation, effectively scattering phonons and improving the power factor. It is observed that the Ni interstitial and Ti,Hf/Sn antisite defects are collectively formed, leading to significant atomic disorder that causes the additional reduction of lattice thermal conductivity. The Ti1-xHfxNiSn1-ySby alloys containing inherent atomic-scale defect disorders are produced in one hour by a newly developed process of temperature-regulated rapid solidification followed by sintering. The collective atomic-scale defect disorder improves the zT to 1.09 +/- 0.12 at 800 K for the Ti0.5Hf0.5NiSn0.98Sb0.02 alloy. These results provide a promising avenue for improving the TE performance of state-of-the-art materials.</P>
Effects of Doping on Transport Properties in Cu–Bi–Se-Based Thermoelectric Materials
Hwang, Jae-Yeol,Mun, Hyeon A.,Kim, Sang Il,Lee, Ki Moon,Kim, Jungeun,Lee, Kyu Hyoung,Kim, Sung Wng American Chemical Society 2014 Inorganic Chemistry Vol.53 No.24
<P>The thermoelectric properties of Zn-, In-, and I-doped Cu<SUB>1.7</SUB>Bi<SUB>4.7</SUB>Se<SUB>8</SUB> pavonite homologues were investigated in the temperature range from 300 to 560 K. On the basis of the comprehensive structural analysis using Rietveld refinement of synchrotron radiation diffraction for Cu<SUB><I>x+y</I></SUB>Bi<SUB>5–<I>y</I></SUB>Se<SUB>8</SUB> compounds with the inherently disordered crystallographic sites, we demonstrate a doping strategy that provides a simultaneous control for enhanced electronic transport properties by the optimization of carrier concentration and exceptionally low lattice thermal conductivity by the formation of point defects. Substituted Zn or In ions on Cu site was found to be an effective phonon scattering center as well as an electron donor, while doping on Bi site showed a moderate effect for phonon scattering. In addition, we achieved largely enhanced power factor in small amount of In doping on Cu site by increased electrical conductivity and moderately decreased Seebeck coefficient. Coupled with a low lattice thermal conductivity originated from intensified point defect phonon scattering by substituted In ions with host Cu ions, a thermoelectric figure of merit <I>ZT</I> of 0.24 at 560 K for Cu<SUB>1.6915</SUB>In<SUB>0.0085</SUB>Bi<SUB>4.7</SUB>Se<SUB>8</SUB> was achieved, yielding 30% enhancement compared with that of a pristine Cu<SUB>1.7</SUB>Bi<SUB>4.7</SUB>Se<SUB>8</SUB> at the same temperature.</P><P>On the basis of structural analysis, it is verified that the structural features, including atomic bonding and configurations, are strongly correlated with both electronic and thermal transport properties in the pavonite homologue Cu<SUB><I>x</I>+<I>y</I></SUB>Bi<SUB>5−<I>y</I></SUB>Se<SUB>8</SUB> system. Extremely low lattice thermal conductivity of 0.32 W m<SUP>−1</SUP> K<SUP>−1</SUP> was achieved at 560 K by Zn doping at interstitial Cu site.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/inocaj/2014/inocaj.2014.53.issue-24/ic5014945/production/images/medium/ic-2014-014945_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ic5014945'>ACS Electronic Supporting Info</A></P>
Strong Enhancement of Superconductivity in Inorganic Electride 12CaO·7Al2O3:e− under High Pressure
Shigeki Tanaka,Tomoki Kato,Atsushi Miyake,Tomoko Kagayama,Katsuya Shimizu,Sung Wng Ki,Satoru Matsuishi,Hideo Hosono 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We present the results of the pressure dependence of the superconductivity of the inorganicelectride 12CaO·7Al2O3:e− (C12A7:e−) single crystal through the ac-susceptibility measurementunder high pressure. C12A7:e− has the cage structure and the density of states derived fromthe cages may play an important role in the superconductivity. The superconducting transitiontemperature (Tc) is 0.2 K at ambient pressure and monotonically increases up to 1.79 K at4.7 GPa. The upper critical field Hc2 and −dHc2/dT at Tc, in proportion to the density of states(DOS) at Fermi energy becomes larger under high pressure. The superconductivity in C12A7:e− ismediated by the electron-phonon interaction, and the increase of Tc with pressure may arise froma peak structure of the DOS of cage conduction band.