Intrinsic Quasi 1-D Lattice Instability and Thermoelectricity in In 4 Se 3-δ y 4 3 δ Jong-Soo Rhyee, C. Cho, K. H. Lee, S. M. Lee, S. I. Kim, g y , , , , , J. H. Shim 1 , Y. S. Kwon 2 , and Gabriel Kotliar 3 Materials Research Center, Samsung Advanced Institute of Technology , g gy 1 Dept. of Chemistry, Pohang University of Science and Technology 2 Dept. of Physics, Sung Kyun Kwan University 3 Dept. of Physics and Astronomy, Rutgers University, USA p y y g y
Low Thermal Conductivity and CDW Low Thermal Conductivity and CDW Extremely low thermal conductivity - 2-D layered WSe 2 thin film - Disordered layered structure Di d d l d t t - κ=0.04 W/mK * Limitations * Limitations - Thin film structure Crystal structure of WSe 2 - Electrical insulator C. Chritescue et al. Science (2007) Charge Density Wave Charge Density Wave (CDW) - Strong electron-phonon coupling Strong electron phonon coupling ψ k ( ε ) - Density wave energy gap - Low D Lattice instability 2 ( ( 0 ) ) ( ( 0 0 ) ) k k V V k k ' ' ∑ = 2 E a+2b − k a-2b 0 0 E E ≠ k k ' k k ' 2 nd order perturbation theory 2 nd d t b ti th 2 2a The 7 th Korea-US Nano Forum Iwha Women’s Univ., 6 th April 2010
Thermoelectric properties of CDW Thermoelectric properties of CDW Toy model – CeTe 2 CeTe 2 -High T CDW -Lattice Lattice distortion along the plane of CDW K. Y. Shin et al. Phys. Rev. B (72) 85132 (2005) CeTe 2 electron diffraction Te-layer distortion Crystal structure of CeTe 2 Thermoelectricity in CeTe 2 - Low thermal conductivity 2 - Low L 1 Seebeck Energy (eV) coefficient 0 -1 -2 Γ X Γ Z M J. S. Rhyee et al. J. Appl. Phys. (105) Energy band 53712 (2009) structure of CeTe 2 Thermal conductivity (left) and Seebeck coefficient of CeTe 2-x Sn x Th l d ti it (l ft) d S b k ffi i t f C T S The 7 th Korea-US Nano Forum Iwha Women’s Univ., 6 th April 2010
Peierls distortion and Thermoelectricity Peierls distortion and Thermoelectricity Quasi-1D Bulk crystal Quasi 1-D In chain in In 4 Se 3 (100) plane O. A. Balitskii et al. Physica E (22) 921 (2004) Y. B. Losovyj et al. Appl. Phys. Lett. (92) 122107 (2008) Crystal structure and TE properties of In 4 Se 3-x - Se-deficiency induced Peierls induced Peierls distortion ab-plane - Low thermal bc-plane conductivity along the plane of Peierls plane of Peierls instability - High ZT (1.48 @705 K) for n-type J. S. Rhyee et al. Nature materials materials I In 4 Se 3 crystal structure S l ( (2009) ) The 7 th Korea-US Nano Forum Iwha Women’s Univ., 6 th April 2010
Peierls distortion and Thermoelectricity Peierls distortion and Thermoelectricity Band structure and Peierls distortion 2 2 c d 1 1 Energy (eV) nergy (eV) 0 0 En E -1 -1 -2 -2 Γ Γ X Z T Y S X U R X Z T Y S X U R TEM and ED of In 4 Se 2.78 along the ab- (a) (c) In 4 Se 3 and (d) In 4 Se 2.75 band structure and bc-planes (b). - Quasi 1-D lattice distortion along the b- axis - Lattice doubling in electron diffraction and generalized electron susceptibility calculation - Semiconducting band gap of In 4 Se 3 - Dispersive electron band and localized J. S. Rhyee et al. hole band of In 4 Se 2.75 Nature (2009) APL (2009) APL (2009) F Fermi surface (a) and generalized electron susceptibility (b) of i f ( ) d li d l t tibilit (b) f In 4 Se 2.75 The 7 th Korea-US Nano Forum Iwha Women’s Univ., 6 th April 2010
Summary and Conclusions Summary and Conclusions Summary 1. Low thermal conductivity • Extremely low thermal conductivity in the layered structure of disordered plane • CDW is an effective way to realize the disordered and layered structure 2. Band structural property of In 4 Se 3-δ • • Asymmetric electron hole band; hole localization Asymmetric electron-hole band; hole localization 3. High thermoelectric performance and Peierls distortion • Peierls distortion of In 4 Se 3-δ • High thermoelectric figure-of-merit (ZT 1.48 @ 705 K) g g ( @ ) Conclusions Possible practical application for waste heat power generation of In 4 Se 3-δ Peierls distortion is a new pathway of thermoelectric materials development The 7 th Korea-US Nano Forum Iwha Women’s Univ., 6 th April 2010
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