Browsing by Author "Zhao, HZ"

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    Structural and dynamic properties of MgAgSb-based thermoelectric materials studied by neutron scattering
    (International Conference on Neutron Scattering, 2017-07-12) Li, XY; Wang, BT; Guidi, T; Avdeev, M; He, LH; Zhao, HZ; Wang, FW
    A breakthrough on thermoelectric materials was recently reported in MgAgSb-based compounds with high ZT value (ZT ~ 1.4 at 450 - 530 K), stimulating the new prospects on the near room temperature (RT) application of thermoelectric generation and solid-state cooling. Here, high resolution neutron powder diffraction (NPD) and inelastic neutron scattering (INS) experiments were performed using ECHIDNA @ ANSTO and MARI @ ISIS, respectively. Rietveld structure refinement of the NPD data indicates that the space group of MgAg0.97Sb0.99 is I-4c2 both at 3 K and 300 K. Combining magnetic and heat-capacity measurements demonstrated that there are no phase transitions between 3 K to RT, in contrast with rich structural phase transitions in the RT - 700 K range. Considering the remarkable crystal-grain-size effect on the thermoelectric performance, we refined the apparent size of ~ 22 nm, validating the TEM result of 10 - 20 nm. We demonstrated that the phonon density of states (PDOS) deduced from MARI data is roughly in agreement with our ab initio calculations. We also analyzed the resonant bonding and LA-TO coupling which are believed to responsible for the low phonon thermal conductivity. Amazingly only 0.5% Ni doping at Ag site reduces the thermal conductivity by more than 8%. High resolution INS experiments to accurately measure the low frequency PDOS will be performed to study the Ni doping effect on the low thermal conductivity mechanism, combining with ab initio calculation.
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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.