Browsing by Author "Le, MD"

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    Gains from the upgrade of the cold neutron triple-axis spectrometer FLEXX at the BER-II reactor
    (Elsevier, 2013-11-21) Le, MD; Quintero-Castro, DL; Toft-Petersen, R; Groitl, F; Skoulatos, M; Rule, KC; Habicht, K
    The upgrade of the cold neutron triple-axis spectrometer FLEXX is described. We discuss the characterisation of the gains from the new primary spectrometer, including a larger guide and double focussing monochromator, and present measurements of the energy and momentum resolution and of the neutron flux of the instrument. We found an order of magnitude gain in intensity (at the cost of coarser momentum resolution), and that the incoherent elastic energy widths are measurably narrower than before the upgrade. The much improved count rate should allow the use of smaller single crystals samples and thus enable the upgraded FLEXX spectrometer to continue making leading edge measurements. © 2013, Elsevier Ltd.
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    Ultralow thermal conductivity from transverse acoustic phonon suppression in distorted crystalline α-MgAgSb
    (Springer Nature, 2020-02-18) Li, XY; Liu, PF; Zhao, EY; Zhang, ZG; Guidi, T; Le, MD; Avdeev, M; Ikeda, K; Otomo, T; Kofu, M; Nakajima, K; Chen, J; He, LH; Ren, Y; Wang, XL; Wang, BT; Ren, ZF; Zhao, HZ; Wang, FW
    Low thermal conductivity is favorable for preserving the temperature gradient between the two ends of a thermoelectric material, in order to ensure continuous electron current generation. In high-performance thermoelectric materials, there are two main low thermal conductivity mechanisms: the phonon anharmonic in PbTe and SnSe, and phonon scattering resulting from the dynamic disorder in AgCrSe2 and CuCrSe2, which have been successfully revealed by inelastic neutron scattering. Using neutron scattering and ab initio calculations, we report here a mechanism of static local structure distortion combined with phonon-anharmonic-induced ultralow lattice thermal conductivity in α-MgAgSb. Since the transverse acoustic phonons are almost fully scattered by the compound’s intrinsic distorted rocksalt sublattice, the heat is mainly transported by the longitudinal acoustic phonons. The ultralow thermal conductivity in α-MgAgSb is attributed to its atomic dynamics being altered by the structure distortion, which presents a possible microscopic route to enhance the performance of similar thermoelectric materials. © The Author(s) 2020.