Condensed-Matter Physics & Materials Science Seminar
"Plastic Deformation at the Nanoscale and Superconductivity Enhancement in Decompression"
Presented by Bin Chen, Shanghai Laboratory of Center for High Pressure Science & Technology Advanced Research (HPSTAR), China
Thursday, April 5, 2018, 1:30 pm — ISB Bldg. 734 Seminar Room 201 (upstairs)
Plastic Deformation at the Nanoscale: Understanding the plastic deformation of nanocrystalline materials is a longstanding challenge [1,2]. Various controversial observations, mainly on the existence of dislocations and the mechanisms for a reversed Hall–Petch effect, have been reported. However, in situ observation of plastic deformation in ultrafine (sub-10 nm) nanocrystals has long been difficult, precluding the direct exploration of mechanics at the nanometer scale. By using a radial diamond-anvil cell (rDAC) x-ray diffraction technique we plastically deformed nickel to pressures above 35 GPa and observed that 1) dislocation-mediated deformation was still operative in as small as 3 nm nickel particles ; 2) 70 nm nickel particles were found to rotate more than any other grain size, signaling the reversal in the size dependence of grain rotation [4,5]; 3). Hall-Petch effect in nickel can be extended to 3 nm . These observations demand considering the role of defects in the physical behaviors of nanomaterials.
Superconductivity Enhancement in Decompression: An unexpected superconductivity enhancement was recently observed in decompressed In2Se3 . The onset of superconductivity in In2Se3 occurred at 41.3 GPa with a critical temperature (Tc) of 3.7 K, peaking at 47.1 GPa. The striking observation shows that this layered chalcogenide remains superconducting during decompression down to 10.7 GPa. More surprisingly, the highest Tc in decompression was 8.2 K, a twofold increase in the same crystal structure as in compression. The novel decompression-induced superconductivity enhancement implies that it is possible to maintain pressure-induced superconductivity at lower or even ambient pressures with better superconducting performance.
 B. Chen, et al., MRS Bulletin 41, 473 (2016).
 H. K. Mao, et al., Matter and Radiation at Extremes, 1, 59 (2016).
 B. Chen, et al., Science 338, 1448 (2012).
 B. Chen, et al., Proc. Natl. Ac
Hosted by: Cedomir Petrovic
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