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Now showing items 1 - 9 of 9

  • Enhanced power factor via the control of structural phase transition in SnSe

    Yu, Hulei   Dai, Shuai   Chen, Yue  

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  • Enhanced out-of-plane electrical transport in n-type SnSe thermoelectrics induced by resonant states and charge delocalization

    Yu, Hulei   Shaikh, Abdul Rehman   Xiong, Fen   Chen, Yue  

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  • Pressure-Stabilized Tin Selenide Phase with an Unexpected Stoichiometry and a Predicted Superconducting State at Low Temperatures

    Yu, Hulei   Lao, Wenxin   Wang, Lijuan   Li, Kuo   Chen, Yue  

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  • Resonant doping in BiCuSeO thermoelectrics from first principles

    Shen, Jiahong   Yu, Hulei   Pei, Yanzhong   Chen, Yue  

    The doping effects of the boron group (Al, Ga, In and Tl) and the nitrogen group elements (As and Sb) on BiCuSeO are studied combining a band unfolding technique and density functional theory. Substitutional site preferences of these dopants are predicted based on the formation energy. It is found that significant resonant states near the conduction band minimum and valence band maximum of BiCuSeO are induced by In and Tl, respectively, providing a guideline for the enhancement of thermoelectric efficiency through band engineering. Effective band structures of the doped systems have been obtained for direct examination of the resonant states. Arsenic tends to substitute either Bi or Se atoms, while the electronic structure strongly depends on the substitutional sites. The decomposed density of states and charge densities are also calculated to unveil the origins of the resonant effects.
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  • Pressure-Induced Ge 2 Se 3 and Ge 3 Se 4 Crystals with Low Superconducting Transition Temperatures

    YU, Hulei   Chen, Yue  

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  • Unexpected High-Pressure Phase of GeTe with an Origin of Low lonicity and Electron Delocalization

    Yu, Hulei   Chen, Yue  

    First-principles evolutionary searches have been to systematically explore the high-pressure phases of germanium telluride. Two new phases are found to be both energetically and dynamically stable under moderate pressures. A Pnma orthorhombic phase with an uncommon "boat" conformation and a P4/nmm tetragonal phase are found to become stable at similar to 15 as and GPa, respectively. The long-believed high-pressure B2 phase, however, is found to be energetically unfavorable comparing to the P4/nmm phase. Our calculations of the electronic structures 13 show that Pnma-boat GeTe and P4/nmm GeTe exhibit semimetallic and metallic behaviors, respectively. On the basis of the electron phonon coupling calculations, P4/nmm GeTe is shown to have a superconducting transition at low temperatures, resulting from its sudden decrease of ionicity and the more delocalized lone-pair electrons. The discovery of these new GeTe phases further enriches our knowledge of the high-pressure behaviors of the IV-VI compounds.
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  • Unveiling a Novel, Cation-Rich Compound in a High-Pressure Pb–Te Binary System

    Yu, Hulei   Lin, Xiaohuan   Li, Kuo   Chen, Yue  

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  • Simultaneous Optimization of Carrier Concentration and Alloy Scattering for Ultrahigh Performance GeTe Thermoelectrics

    Li, Juan   Chen, Zhiwei   Zhang, Xinyue   Yu, Hulei   Wu, Zihua   Xie, Huaqing   Chen, Yue   Pei, Yanzhong  

    In order to locate the optimal carrier concentrations for peaking the thermoelectric performance in p-type group IV monotellurides, existing efforts focus on aliovalent doping, either to increase (in PbTe) or to decrease (in SnTe and GeTe) the hole concentration. The limited solubility of aliovalent dopants usually introduces insufficient phonon scattering for thermoelectric performance maximization. With a decrease in the size of cation, the concentration of holes, induced by cation vacancies in intrinsic compounds, increases rapidly from approximate to 10(18) cm(-3) in PbTe to approximate to 10(20) cm(-3) in SnTe and then to approximate to 10(21) cm(-3) in GeTe. This motivates a strategy here for reducing the carrier concentration in GeTe, by increasing the mean size of cations and vice-versa decreasing the average size of anions through isovalent substitutions for increased formation energy of cation vacancy. A combination of the simultaneously resulting strong phonon scattering due to the high solubility of isovalent impurities, an ultrahigh thermoelectric figure of merit, zT of 2.2 is achieved in GeTe-PbSe alloys. This corresponds to a 300% enhancement in average zT as compared to pristine GeTe. This work not only demonstrates GeTe as a promising thermoelectric material but also paves the way for enhancing the thermoelectric performance in similar materials.
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  • Unraveling a novel ferroelectric GeSe phase and its transformation into a topological crystalline insulator under high pressure

    Yu, Hulei   Gao, Dexiang   Wang, Xiancheng   Du, Xueyan   Lin, Xiaohuan   Guo, Wenhan   Zou, Ruqiang   Jin, Changqing   Li, Kuo   Chen, Yue  

    Germanium selenide is a promising material for electronic, photovoltaic, and thermoelectric applications; however, structural phase transitions of GeSe under pressure are controversial. Combining evolutionary algorithms, density functional theory, tight-binding method, and laser-heated diamond anvil cell experiments, pressure-induced phase transitions of GeSe are thoroughly investigated. Two novel intermediate phases are predicted to exist in between the well-known alpha-GeSe and the recently discovered beta-GeSe under high pressure. alpha-GeSe is found to transform into a rhombohedral crystal structure with a space group of R3m at a low hydrostatic pressure. The R3m phase of GeSe exhibits robust ferroelectricity analogous to GeTe. By further increasing the pressure to approximately 6 GPa, the R3m phase is predicted to transform into a rock-salt structure, becoming a 3D topological crystalline insulator with an inverted band structure. The newly discovered GeSe high-pressure phases greatly enrich our knowledge of IV-VI compounds.
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