Grasping the underlying mechanisms behind the low lattice thermal conductivity of materials is essential for the efficient design and development of high-performance thermoelectric materials and thermal barrier coatin...Grasping the underlying mechanisms behind the low lattice thermal conductivity of materials is essential for the efficient design and development of high-performance thermoelectric materials and thermal barrier coating materials.In this paper,we present a first-principles calculations of the phonon transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers.Both materials possess low lattice thermal conductivity,at least two orders of magnitude lower than graphene and h-BN.The room temperature thermal conductivity of Pb_(2)SbAs(0.91 W/m K)is only a quarter of that of Pb_(2)PAs(3.88 W/m K).We analyze in depth the bonding,lattice dynamics,and phonon mode level information of these materials.Ultimately,it is determined that the synergistic effect of low group velocity due to weak bonding and strong phonon anharmonicity is the fundamental cause of the intrinsic low thermal conductivity in these Janus structures.Relative regular residual analysis further indicates that the four-phonon processes are limited in Pb_(2)PAs and Pb_(2)SbAs,and the three-phonon scattering is sufficient to describe their anharmonicity.In this study,the thermal transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers are illuminated based on fundamental physical mechanisms,and the low lattice thermal conductivity endows them with the potential applications in the field of thermal barriers and thermoelectrics.展开更多
The gamma-graphyne nanoribbons(γ-GYNRs) incorporating diamond-shaped segment(DSSs) with excellent thermoelectric properties are systematically investigated by combining nonequilibrium Green’s functions with adaptive...The gamma-graphyne nanoribbons(γ-GYNRs) incorporating diamond-shaped segment(DSSs) with excellent thermoelectric properties are systematically investigated by combining nonequilibrium Green’s functions with adaptive genetic algorithm. Our calculations show that the adaptive genetic algorithm is efficient and accurate in the process of identifying structures with excellent thermoelectric performance. In multiple rounds, an average of 476 candidates(only 2.88% of all16512 candidate structures) are calculated to obtain the structures with extremely high thermoelectric conversion efficiency.The room temperature thermoelectric figure of merit(ZT) of the optimal γ-GYNR incorporating DSSs is 1.622, which is about 5.4 times higher than that of pristine γ-GYNR(length 23.693 nm and width 2.660 nm). The significant improvement of thermoelectric performance of the optimal γ-GYNR is mainly attributed to the maximum balance of inhibition of thermal conductance(proactive effect) and reduction of thermal power factor(side effect). Moreover, through exploration of the main variables affecting the genetic algorithm, it is revealed that the efficiency of the genetic algorithm can be improved by optimizing the initial population gene pool, selecting a higher individual retention rate and a lower mutation rate. The results presented in this paper validate the effectiveness of genetic algorithm in accelerating the exploration of γ-GYNRs with high thermoelectric conversion efficiency, and could provide a new development solution for carbon-based thermoelectric materials.展开更多
Rashba spin splitting(RSS)and quantum spin Hall effect(QSHE)have attracted enormous interest due to their great significance in the application of spintronics.In this work,we theoretically proposed a new two-dimension...Rashba spin splitting(RSS)and quantum spin Hall effect(QSHE)have attracted enormous interest due to their great significance in the application of spintronics.In this work,we theoretically proposed a new two-dimensional(2D)material H–Pb–F with coexistence of giant RSS and quantum spin Hall effec by using the ab initio calculations.Our results show that H–Pb–F possesses giant RSS(1.21 eV·A)and the RSS can be tuned up to 4.16 e V·A by in-plane biaxial strain,which is a huge value among 2D materials.Furthermore,we also noticed that H–Pb–F is a 2D topological insulator(TI)duo to the strong spin–orbit coupling(SOC)interaction,and the large topological gap is up to 1.35 e V,which is large enough for for the observation of topological edge states at room temperature.The coexistence of giant RSS and quantum spin Hall effect greatly broadens the potential application of H–Pb–F in the field of spintronic devices.展开更多
Using Green＇s function method, we investigate the spin transport properties of armchair graphene nanoribbons （AG- NRs） under magnetic field and uniaxial strain. Our results show that it is very difficult to transfo...Using Green＇s function method, we investigate the spin transport properties of armchair graphene nanoribbons （AG- NRs） under magnetic field and uniaxial strain. Our results show that it is very difficult to transform narrow AGNRs directly from semiconductor to spin gapless semiconductors （SGS） by applying magnetic fields. However, as a uniaxial strain is exerted on the nanoribbons, the AGNRs can transform to SGS by a small magnetic field. The combination mode be- tween magnetic field and uniaxial strain displays a nonmonotonic arch-pattern relationship. In addition, we find that the combination mode is associated with the widths of nanoribbons, which exhibits group behaviors.展开更多
Using first-principles calculations combined with the Boltzmann transport theory,we explore the thermoelectric properties of natural superlattice(SL)structure Sb_(2)Te.The results show that n-type Sb_(2)Te possesses l...Using first-principles calculations combined with the Boltzmann transport theory,we explore the thermoelectric properties of natural superlattice(SL)structure Sb_(2)Te.The results show that n-type Sb_(2)Te possesses larger Seebeck coefficient of 249.59(318.87)μV/K than p-type Sb_(2)Te of 219.85(210.38)μV/K and low lattice thermal conductivity of 1.25(0.21)W/mK along the in-plane(out-of-plane)direction at 300 K.The excellent electron transport performance is mainly attributed to steeper density of state around the bottom of conduction band.The ultralow lattice thermal conductivity of Sb_(2)Te is mainly caused by low phonon group velocity and strong anharmonicity.Further analysis shows that the decrease of group velocity comes from flatter dispersion curves which are contributed by the Brillouin-zone folding.The strong anharmonicity is mainly due to the presence of lone-pair electrons in Sb_(2)Te.Combining such a high Seebeck coefficient with the low lattice thermal conductivity,maximum n-type thermoelectric figure of merit(ZT)of 1.46 and 1.38 could be achieved along the in-plane and out-of-plane directions at room temperature,which is higher than the reported values of Sb_(2)Te_(3).The findings presented here provide insight into the transport property of Sb_(2)Te and highlight potential applications of thermoelectric materials at room temperature.展开更多
The diamond-like cubic silicon(d-Si)is widely used in modern electronics and solar cell industries.However,it is not an optimal candidate for thermoelectric application due to its high lattice thermal conductivity.Si(...The diamond-like cubic silicon(d-Si)is widely used in modern electronics and solar cell industries.However,it is not an optimal candidate for thermoelectric application due to its high lattice thermal conductivity.Si(oP32)is a recently predicted orthorhombic silicon allotrope,whose total energy is close to that of d-Si.Using first-principles calculations and Boltzmann transport theory,we systematically investigate the thermoelectric properties of Si(oP32).The lower phonon thermal conductivity and higher power factor are obtained in Si(oP32)than those in diamond silicon.The low phonon thermal conductivity(33.77 W/mK at 300 K)is mainly due to the reduction of the phonon group velocity and enhancement of phonon-phonon scattering(including scattering phase space and strength).Meanwhile,the results also show that the thermoelectric performance along the zz lattice direction is better than that along the xx and yy lattice directions,and the figure of merit(700 K)along the zz lattice direction could approach to 2.45 and 1.75 for p-type and n-type Si(oP32),respectively.The values are much higher than those of d-Si(about 0.06))and Si24(0.6),indicating that the Si(oP32)is a promising candidate for thermoelectric applications.Our theoretical studies shed light on the thermoelectric properties of Si(oP32)and could stimulate further experimental studies.展开更多
By the Green＇s function method,we investigate spin transport properties of a zigzag graphene nanoribbon superlattice（ZGNS） under a ferromagnetic insulator and edge effect.The exchange splitting induced by the ferro...By the Green＇s function method,we investigate spin transport properties of a zigzag graphene nanoribbon superlattice（ZGNS） under a ferromagnetic insulator and edge effect.The exchange splitting induced by the ferromagnetic insulator eliminates the spin degeneracy,which leads to spin-polarized transport in structure.Spin-dependent minibands and minigaps are exhibited in the conductance profile near the Fermi energy.The location and width of the miniband are associated with the geometry of the ZGNS.In the optimal structure,the spin-up and spin-down minibands can be separated completely near the Fermi energy.Therefore,a wide,perfect spin polarization with clear stepwise pattern is observed,i.e.,the perfect spin-polarized transport can be tuned from spin up to spin down by varying the electron energy.展开更多
Owing to the interaction between the layers,the twisted bilayer two-dimensional(2 D)materials exhibit numerous unique optical and electronic properties different from the monolayer counterpart,and have attracted treme...Owing to the interaction between the layers,the twisted bilayer two-dimensional(2 D)materials exhibit numerous unique optical and electronic properties different from the monolayer counterpart,and have attracted tremendous interests in current physical research community.By means of first-principles and tight-binding model calculations,the electronic properties of twisted bilayer biphenylene carbon(BPC)are systematically investigated in this paper.The results indicate that the effect of twist will not only leads to a phase transition from semiconductor to metal,but also an adjustable band gap in BPC(0 me V to 120 me V depending on the twist angle).Moreover,unlike the twisted bilayer graphene(TBG),the flat bands in twisted BPC are no longer restricted by"magic angles",i.e.,abnormal flat bands could be appeared as well at several specific large angles in addition to the small angles.The charge density of these flat bands possesses different local modes,indicating that they might be derived from different stacked modes and host different properties.The exotic physical properties presented in this work foreshow twisted BPC a promising material for the application of terahertz and infrared photodetectors and the exploration of strong correlation.展开更多
基金Project supported by the Youth Science and Technology Talent Project of Hunan Province of China (Grant No.2022RC1197)the National Natural Science Foundation of China (Grant No.52372260)。
文摘Grasping the underlying mechanisms behind the low lattice thermal conductivity of materials is essential for the efficient design and development of high-performance thermoelectric materials and thermal barrier coating materials.In this paper,we present a first-principles calculations of the phonon transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers.Both materials possess low lattice thermal conductivity,at least two orders of magnitude lower than graphene and h-BN.The room temperature thermal conductivity of Pb_(2)SbAs(0.91 W/m K)is only a quarter of that of Pb_(2)PAs(3.88 W/m K).We analyze in depth the bonding,lattice dynamics,and phonon mode level information of these materials.Ultimately,it is determined that the synergistic effect of low group velocity due to weak bonding and strong phonon anharmonicity is the fundamental cause of the intrinsic low thermal conductivity in these Janus structures.Relative regular residual analysis further indicates that the four-phonon processes are limited in Pb_(2)PAs and Pb_(2)SbAs,and the three-phonon scattering is sufficient to describe their anharmonicity.In this study,the thermal transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers are illuminated based on fundamental physical mechanisms,and the low lattice thermal conductivity endows them with the potential applications in the field of thermal barriers and thermoelectrics.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11974300,11974299,12074150)the Natural Science Foundation of Hunan Province,China(Grant No.2021JJ30645)+3 种基金Scientific Research Fund of Hunan Provincial Education Department(Grant Nos.20K127,20A503,and 20B582)Program for Changjiang Scholars and Innovative Research Team in University(Grant No.IRT13093)the Hunan Provincial Innovation Foundation for Postgraduate(Grant No.CX20220544)Youth Science and Technology Talent Project of Hunan Province,China(Grant No.2022RC1197)。
文摘The gamma-graphyne nanoribbons(γ-GYNRs) incorporating diamond-shaped segment(DSSs) with excellent thermoelectric properties are systematically investigated by combining nonequilibrium Green’s functions with adaptive genetic algorithm. Our calculations show that the adaptive genetic algorithm is efficient and accurate in the process of identifying structures with excellent thermoelectric performance. In multiple rounds, an average of 476 candidates(only 2.88% of all16512 candidate structures) are calculated to obtain the structures with extremely high thermoelectric conversion efficiency.The room temperature thermoelectric figure of merit(ZT) of the optimal γ-GYNR incorporating DSSs is 1.622, which is about 5.4 times higher than that of pristine γ-GYNR(length 23.693 nm and width 2.660 nm). The significant improvement of thermoelectric performance of the optimal γ-GYNR is mainly attributed to the maximum balance of inhibition of thermal conductance(proactive effect) and reduction of thermal power factor(side effect). Moreover, through exploration of the main variables affecting the genetic algorithm, it is revealed that the efficiency of the genetic algorithm can be improved by optimizing the initial population gene pool, selecting a higher individual retention rate and a lower mutation rate. The results presented in this paper validate the effectiveness of genetic algorithm in accelerating the exploration of γ-GYNRs with high thermoelectric conversion efficiency, and could provide a new development solution for carbon-based thermoelectric materials.
基金the National Natural Science Foundation of China(Grant Nos.11874316,11404275,and 11474244)the National Basic Research Program of China(Grant No.2015CB921103)+2 种基金the Natural Science Foundation of Hunan Province,China(Grant Nos.2016JJ3118 and 2020JJ4244)the Scientific Research Foundation of the Education Bureau of Hunan Province,China(Grant Nos.16K084,17K086,and 21A049)the Fund for the Innovative Research Team in University(Grant No.IRT13093).
文摘Rashba spin splitting(RSS)and quantum spin Hall effect(QSHE)have attracted enormous interest due to their great significance in the application of spintronics.In this work,we theoretically proposed a new two-dimensional(2D)material H–Pb–F with coexistence of giant RSS and quantum spin Hall effec by using the ab initio calculations.Our results show that H–Pb–F possesses giant RSS(1.21 eV·A)and the RSS can be tuned up to 4.16 e V·A by in-plane biaxial strain,which is a huge value among 2D materials.Furthermore,we also noticed that H–Pb–F is a 2D topological insulator(TI)duo to the strong spin–orbit coupling(SOC)interaction,and the large topological gap is up to 1.35 e V,which is large enough for for the observation of topological edge states at room temperature.The coexistence of giant RSS and quantum spin Hall effect greatly broadens the potential application of H–Pb–F in the field of spintronic devices.
基金supported by the National Basic Research Program of China(Grant No.2012CB921303)the National Natural Science Foundation of China(Grant Nos.51172191,11074211,11074213,51006086,and 51176161)the Joint Funds of the Natural Science Foundation of Hunan Province,China(Grant No.10JJ9001)
文摘Using Green＇s function method, we investigate the spin transport properties of armchair graphene nanoribbons （AG- NRs） under magnetic field and uniaxial strain. Our results show that it is very difficult to transform narrow AGNRs directly from semiconductor to spin gapless semiconductors （SGS） by applying magnetic fields. However, as a uniaxial strain is exerted on the nanoribbons, the AGNRs can transform to SGS by a small magnetic field. The combination mode be- tween magnetic field and uniaxial strain displays a nonmonotonic arch-pattern relationship. In addition, we find that the combination mode is associated with the widths of nanoribbons, which exhibits group behaviors.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11974300,11974299,and 11704319)the Natural Science Foundation of Hunan Province,China(Grant No.2021JJ30645)+2 种基金the Scientific Research Fund of Hunan Provincial Education Department,China(Grant Nos.20K127,20A503,and 20B582)the Program for Changjiang Scholars and Innovative Research Team in Universities(Grant No.IRT13093)the Hunan Provincial Innovation Foundation for Postgraduate Students,China(Grant No.CX20200624)。
文摘Using first-principles calculations combined with the Boltzmann transport theory,we explore the thermoelectric properties of natural superlattice(SL)structure Sb_(2)Te.The results show that n-type Sb_(2)Te possesses larger Seebeck coefficient of 249.59(318.87)μV/K than p-type Sb_(2)Te of 219.85(210.38)μV/K and low lattice thermal conductivity of 1.25(0.21)W/mK along the in-plane(out-of-plane)direction at 300 K.The excellent electron transport performance is mainly attributed to steeper density of state around the bottom of conduction band.The ultralow lattice thermal conductivity of Sb_(2)Te is mainly caused by low phonon group velocity and strong anharmonicity.Further analysis shows that the decrease of group velocity comes from flatter dispersion curves which are contributed by the Brillouin-zone folding.The strong anharmonicity is mainly due to the presence of lone-pair electrons in Sb_(2)Te.Combining such a high Seebeck coefficient with the low lattice thermal conductivity,maximum n-type thermoelectric figure of merit(ZT)of 1.46 and 1.38 could be achieved along the in-plane and out-of-plane directions at room temperature,which is higher than the reported values of Sb_(2)Te_(3).The findings presented here provide insight into the transport property of Sb_(2)Te and highlight potential applications of thermoelectric materials at room temperature.
基金Project supported by the Program for Changjiang Scholars and Innovative Research Team in University,China(Grant No.IRT13093)the National Natural Science Foundation of China(Grant Nos.11304262 and 11404275)+2 种基金the Scientific Research Fund of Hunan Provincial Education Department,China(Grant Nos.17B252,17K086,and 16K084)the Natural Science Foundation of Hunan Province,China(Grant No.2016JJ3118)the Xiangtan University Innovation Foundation for Postgraduate,Hunan Province,China(Grant No.XDCX2020B095).
文摘The diamond-like cubic silicon(d-Si)is widely used in modern electronics and solar cell industries.However,it is not an optimal candidate for thermoelectric application due to its high lattice thermal conductivity.Si(oP32)is a recently predicted orthorhombic silicon allotrope,whose total energy is close to that of d-Si.Using first-principles calculations and Boltzmann transport theory,we systematically investigate the thermoelectric properties of Si(oP32).The lower phonon thermal conductivity and higher power factor are obtained in Si(oP32)than those in diamond silicon.The low phonon thermal conductivity(33.77 W/mK at 300 K)is mainly due to the reduction of the phonon group velocity and enhancement of phonon-phonon scattering(including scattering phase space and strength).Meanwhile,the results also show that the thermoelectric performance along the zz lattice direction is better than that along the xx and yy lattice directions,and the figure of merit(700 K)along the zz lattice direction could approach to 2.45 and 1.75 for p-type and n-type Si(oP32),respectively.The values are much higher than those of d-Si(about 0.06))and Si24(0.6),indicating that the Si(oP32)is a promising candidate for thermoelectric applications.Our theoretical studies shed light on the thermoelectric properties of Si(oP32)and could stimulate further experimental studies.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 51006086,11074213,and 51176161)the Open Fund Based on Innovation Platform of Hunan Colleges and Universities,China (Grant No. 09K034)the Joint Funds of Hunan Provincial Natural Science Foundation,China (Grant No. 10JJ9001)
文摘By the Green＇s function method,we investigate spin transport properties of a zigzag graphene nanoribbon superlattice（ZGNS） under a ferromagnetic insulator and edge effect.The exchange splitting induced by the ferromagnetic insulator eliminates the spin degeneracy,which leads to spin-polarized transport in structure.Spin-dependent minibands and minigaps are exhibited in the conductance profile near the Fermi energy.The location and width of the miniband are associated with the geometry of the ZGNS.In the optimal structure,the spin-up and spin-down minibands can be separated completely near the Fermi energy.Therefore,a wide,perfect spin polarization with clear stepwise pattern is observed,i.e.,the perfect spin-polarized transport can be tuned from spin up to spin down by varying the electron energy.
基金the National Natural Science Foundation of China(Grant No.11874314)the Natural Science Foundation of Hunan Province,China(Grant No.2018JJ2377)。
文摘Owing to the interaction between the layers,the twisted bilayer two-dimensional(2 D)materials exhibit numerous unique optical and electronic properties different from the monolayer counterpart,and have attracted tremendous interests in current physical research community.By means of first-principles and tight-binding model calculations,the electronic properties of twisted bilayer biphenylene carbon(BPC)are systematically investigated in this paper.The results indicate that the effect of twist will not only leads to a phase transition from semiconductor to metal,but also an adjustable band gap in BPC(0 me V to 120 me V depending on the twist angle).Moreover,unlike the twisted bilayer graphene(TBG),the flat bands in twisted BPC are no longer restricted by"magic angles",i.e.,abnormal flat bands could be appeared as well at several specific large angles in addition to the small angles.The charge density of these flat bands possesses different local modes,indicating that they might be derived from different stacked modes and host different properties.The exotic physical properties presented in this work foreshow twisted BPC a promising material for the application of terahertz and infrared photodetectors and the exploration of strong correlation.
