Name:
Xun Shi
Education:
Ph.D
Positions:
Academic title:
Professor
Phone:
021-52412803
Fax:
E-mail:
xshi@mail.sic.ac.cn
Personal Website:
Postal Code:
200050
Mailing Address:
1295 Dingxi Road, Shanghai, P.R.China
Resume:

  Education:

  1995-2000,Bachelor of Material Science and Engineering, Tsinghua University, Beijing, China
  2000-2005,Ph.D. in Material Science and Engineering, Shanghai Institute of Ceramics, Chinese Academy of Sciences, China

  Professional Experience:

  2005-2007,Postdoctor, Department of Physics, University of Michigan, USA
  2007-2010,Material Processing Scientist, GM R&D center (Optimal Incorporated), USA
  2010-current,Professor, State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Science, Shanghai, China

  Awards and Honors :

  Second Prize of National Natural Science Award of China(2013)
  The National Science Fund of China for Excellent Young Scholars(2012)
  Shanghai Natural Science Prize(2012)
  CAS International Cooperation Award for Young Scientists(2012)
  Shanghai Pujiang Program(2011)
  One Hundred Person Project of The Chinese Academy of Sciences(2011)
  Young Investigator Award, International Thermoelectric Society (2010)

  Research: electrical and thermal transport, thermoelectric materials 

  1. Phonon-liquid Electron-crystal materials 

    Solid state materials like traditional glasses and crystals propagate heat through longitudinal and transverse waves. The reduction of lattice thermal conductivity in these traditional solid materials is limited to the value of a glass. However, a liquid does not propagate sheer vibrations. As a result, a liquid material should have less heat conductive. Semiconductor Cu2-δX has a rigid face-centered cubic Se sublattice to provide a crystalline pathway for semiconducting electrons (or more precisely holes). The copper ions are highly disordered around the X sublattice and are superionic with liquid-like mobility.  This extraordinary ‘liquid-like’ behavior of copper ions around a crystalline sublattice of X could eliminate some of the vibrational modes in Cu2-δX as well as strongly scatter heat transferred phonons.  As a result, intrinsically very low lattice thermal conductivity and high zT value of 1.5-1.7 in this otherwise simple semiconductor could be achieved.  This is among the highest values for any bulk thermoelectric materials.   This unusual combination of properties leads to an ideal thermoelectric material within the new concept of ‘Phonon-liquid electron-crystal’.  

   

  2. Diamond-like compounds 

  Current TE materials usually possess high symmetry crystal structures that support the presence of highly degenerate, multi-valley electronic bands yielding good electronic properties characterized by a large power factor. As a consequence, most of the state-of-the-art TE materials have cubic structures with degenerate band edges and symmetry-related multi-valley carrier pockets. Typical examples are SiGe alloys, PbTe, skutterudites, half-Heusler alloys, Mg2Si, and liquid-like Cu2Se. A notable exception is Bi2Te3 and compounds based on it that have comparatively high hexagonal symmetry. This severely restricts the exploration of TE materials to a small percentage of semiconductors that possess high-symmetry cubic structures, and thus excludes a large number of low-symmetry non-cubic materials even though they might manifest ideal band gaps and low thermal conductivities. It remains a key challenge to discover or design novel high-performance TE compounds among non-cubic materials. Taking a hint from the recently emerging chalcopyrite TE materials with reasonable zT values, a new strategy is proposed to design high performance non-cubic thermoelectric materials through the utilization of a rational pseudocubic structure that assures cubic-like degenerate electronic bands via the coexistence of long-range cubic framework with short-range non-cubic lattice distortions. The pseudocubic approach leads to a simple selection rule, that is to maintain the distortion parameter near unity, to identify a series of novel chalcopyrites with zT values enhanced significantly above the unity. This work represents a new paradigm in the search and design of a large variety of non-cubic high-performance thermoelectric materials. 

   

  3.Phase transition and electrical and thermal transports 

  Electronic industry focuses specially on the potential to rapidly cool microprocessors and sensors by the technology within a relatively narrow temperature range around or slightly above room temperature. A significantly improved thermoelectric performance by utilizing critical electron and phonon scattering that takes place during a continuous phase transition. Using iodine-doped Cu2Se where the critical phase transition temperature can be tuned to within a few tens of degrees around room temperature, we show that critical scattering greatly enhances the thermopower and strongly diminishes thermal conductivity, leading to a dramatic increase in zT by a factor of 3-7 times culminating in zT values of 2.3 at 400 K. This new mechanism provides great opportunities for zT enhancement in materials displaying second-order phase transitions near ambient temperature and is appealing for a more extensive use of thermoelectrics in electronic industry. 

   

  4. Caged compounds 

  The traditional high efficiency thermoelectric materials are solid crystalline semiconductor compounds. Good electronic properties are maintained by crystalline semiconductor structure while low lattice thermal conductivity is achieved by varies of methods and approaches to scatter heat transfer phonons. Laboratory results suggest that high zT values can be realized in several families of materials, such as caged compounds skutterudites and clathrates. 

  Publications: 

  1. Ying He, Tristan Day, Tiansong Zhang, Huili Liu, Xun Shi,* Lidong Chen,* G. Jeffrey Snyder*, “High thermoelectric performance in non-toxic earth-abundant copper sulfide”, Advanced Materials (in press). 
  2. Jiawei Zhang, Ruiheng Liu, Nian Cheng, Yubo Zhang, Jihui Yang, Ctirad Uher, Xun Shi*, Lidong Chen*, Wenqing Zhang*, “High-performance pseudocubic thermoelectric materials from non-cubic chalcopyrite compounds”, Advanced Materials (in press). 
  3. Yinglu Tang, Yuting Qiu, Lili Xi, Xun Shi*, Wenqing Zhang, Lidong Chen,  Ssu-Ming Tseng, Sinn-wen Chen, G. Jeffrey Snyder*, “Phase diagram of In–Co–Sb system and thermoelectric properties of In-containing skutterudites”,   Energy & Environmental Science 7, pp 812-819, 2014. 
  4. Yuting Qiu, Juanjuan Xing, Xiang Gao, Lili Xi, Xun Shi*, Hui Gu, Lidong Chen*, “Electrical properties and microcosmic study on compound defects in Ga-contained thermoelectric skutterudites”, Journal of Materials Chemistry A (published online). 
  5. Huili Liu, Xun Yuan, Ping Lu, Xun Shi*, Fangfang Xu, Ying He, Yunshan Tang, Shengqiang Bai, Wenqing Zhang*, Lidong Chen*, Yue Lin, Lei Shi, He Lin, Xingyu Gao, Xingmin Zhang, Hang Chi, Ctirad Uher, “Ultrahigh thermoelectric performance by electron and phonon critical scattering in Cu2 Se1-xIx”, Advanced Materials 25, pp 6607–6612, 2013.  
  6. Tristan Day, Fivos Drymiotis, Tiansong Zhang, Daniel Rhodes, Xun Shi,   Lidong Chen, G. Jeffrey Snyder, “Evaluating the potential for high thermoelectric efficiency of silver selenide”, Journal of Materials Chemistry C 1, pp 7568-7573, 2013. 
  7. Yuting Qiu, Lili Xi, Xun Shi*, Pengfei Qiu, Wenqing Zhang*, Lidong Chen, James R. Salvador, Jung Y. Cho, Jihui Yang, Yuan-chun Chien, Sinn-wen Chen, Yinglu Tang, G. Jeffrey Snyder*, “Charge-Compensated compound defects in Ga-containing thermoelectric skutterudites”, Advanced Functional Materials 23, pp 3194-3203, 2013. 
  8. Pengfei Qiu, Xun Shi*, Yuting Qiu, Xiangyang Huang, Sun Wan, Wenqing Zhang, Lidong Chen, Jihui Yang, “Enhancement of thermoelectric performance in slightly charge-compensated CeyCo4Sb12 skutterudites”, Applied Physics Letters 103, pp 062103, 2013. 
  9. Jing Fan, Huili Liu, Xiaoya Shi, Shengqiang Bai, Xun Shi*, Lidong Chen, “Investigation of thermoelectric properties of Cu2GaxSn1-xSe3 diamond-like compounds by hot pressing and spark plasma sintering”, Acta Materialia, 61(11), pp 4297-4304, 2013/6. 
  10. Huili Liu, Xun Shi*, M. Kirkham, Hsin Wang, Qiang Li, Ctirad Uher, Wenqing Zhang*, Lidong Chen*, “Structure-transformation-induced abnormal thermoelectric properties in semiconductor copper selenide”, Materials Letters 93, pp 121-124, 2013. 
  11. Huili Liu, Xun Shi*, Fangfang Xu, Linlin Zhang, Wenqing Zhang, Lidong Chen*, Qiang Li, Ctirad Uher, Tristan Day, G Jeffery Snyder, “Copper ion liquid-like thermoelectrics”,  Nature Materials 11, pp 422-425, 2012. 
  12. Ruiheng Liu, Lili Xi, Huili Liu, Xun Shi,* Wenqing Zhang, Lidong Chen*, “Ternary compound CuInTe2: a promising thermoelectric material with diamond-like structure”, Chemical Communications 48(32), pp 3818-3820, 2012. 
  13. Peifeng Qiu, Ruiheng Liu, Jiong Yang, Xun Shi*, Xiangyang Huang, Wenqing Zhang,  Lidong Chen, Jihui Yang, David J Singh, “Thermoelectric properties of Ni-doped CeFe4Sb12 skutterudites” Journal of Applied Physics 111, pp 023705, 2012.

  Details: http://english.sic.cas.cn/rh/RD/skl/rf/cld/Leader/

 


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