Browsing by Author "Li, XY"
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- ItemCrystal-liquid duality driven ultralow two-channel thermal conductivity in α-MgAgSb(AIP Publishing, 2024-03) Li, JY; Li, XY; Zhang, YS; Zhu, J; Zhao, E; Kofu, M; Nakajima, K; Avdeev, M; Liu, PF; Sui, Jiehe; Zhao, HSZ; Wang, FW; Zhang, JRThe desire for intrinsically low lattice thermal conductivity (κL) in thermoelectrics motivates numerous efforts on understanding the microscopic mechanisms of heat transport in solids. Here, based on theoretical calculations, we demonstrate that α-MgAgSb hosts low-energy localized phonon bands and avoided crossing of the rattler modes, which coincides with the inelastic neutron scattering result. Using the two-channel lattice dynamical approach, we find, besides the conventional contribution (∼70% at 300 K) from particlelike phonons propagating, the coherence contribution dominated by the wavelike tunneling of phonons accounts for ∼30% of the total κL at 300 K. By considering dual contributions, our calculated room-temperature κL of 0.64 W m−1 K−1 well agrees with the experimental value of 0.63 W m−1 K−1. More importantly, our computations give a nonstandard κL ∝ T−0.61 dependence, perfectly explaining the abnormal temperature-trend of ∼T−0.57 in experiment for α-MgAgSb. By molecular dynamics simulation, we reveal that the structure simultaneously has soft crystalline sublattices with the metavalent bonding and fluctuating liquid-like sublattices with thermally induced large amplitude vibrations. These diverse forms of chemical bonding arouse mixed part-crystal part-liquid state, scatter strongly heat-carrying phonons, and finally produce extremely low κL. The fundamental research from this study will accelerate the design of ultralow-κL materials for energy-conversion applications. © 2024 AIP Publishing LLC
- ItemGrain size and structure distortion characterization of α-MgAgSb thermoelectric material by powder diffraction(IOP Publishing, 2020-05-21) Li, XY; Zhang, Z; He, L; Avdeev, M; Ren, Y; Zhao, H; Wang, FNanostructuring, structure distortion, and/or disorder are the main manipulation techniques to reduce the lattice thermal conductivity and improve the figure of merit of thermoelectric materials. A single-phase α-MgAgSb sample, MgAg0.97Sb0.99, with high thermoelectric performance in near room temperature region was synthesized through a high-energy ball milling with a hot-pressing method. Here, we report the average grain size of 24–28 nm and the accurate structure distortion, which are characterized by high-resolution neutron diffraction and synchrotron x-ray diffraction with Rietveld refinement data analysis. Both the small grain size and the structure distortion have a contribution to the low lattice thermal conductivity in MgAg0.97Sb0.99. © 2020 Chinese Physical Society and IOP Publishing Ltd
- ItemStructural 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, FWA 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.
- ItemUltralow 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, FWLow 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.