Bi_(1-x)Ho_(x)VO_(4)(0.1≤x≤0.9)ceramics were prepared via a solid-state reaction method,and all the ceram-ics could be well densified in the 920–980℃range.The ceramics with 0.1≤x<0.4 were composed of both mono...Bi_(1-x)Ho_(x)VO_(4)(0.1≤x≤0.9)ceramics were prepared via a solid-state reaction method,and all the ceram-ics could be well densified in the 920–980℃range.The ceramics with 0.1≤x<0.4 were composed of both monoclinic scheelite(M)and tetragonal zircon(T)phases,and a single M phase could be obtained in the range of x≥0.4.The measuredε_(r) decreased from 58.9(x=0.1)to 14.7(x=0.9),so do the calcu-lated values(ε_(r)(C−M)=34.3–12.1),and the main reason forε_(r)>ε_(r)(C−M)was the rattling of Ho^(3+)in the dodecahedron.Two points with zeroτf appeared in Bi1–x Hox VO4(0≤x≤1)ceramics,and the best mi-crowave dielectric properties withε_(r)=16.6,Q×f=18,400 GHz(f=10.69 GHz),andτf=+3.29 ppm/℃were obtained in the Bi_(0.2)Ho_(0.8)VO_(4)ceramic.The change in temperature coefficient of ionic polarizability(τ_(αm))caused by the rattling effect of cations is the physical essence that affectsτf.Therefore,the rattling effect can be used as an effective mechanism to regulateτf in low-ε_(r) materials.Furthermore,there was no chemical reaction between Bi_(1-x)Ho_(x)VO_(4) and Ag electrode,which indicates potential applications in low-temperature co-fired ceramic(LTCC)technology.展开更多
The competition between different magnetic structures in hole-doped Fe-pnicitides is explored based on an extended five-orbital Hubbard model including long-range Coulomb interactions.Our results show that the stabili...The competition between different magnetic structures in hole-doped Fe-pnicitides is explored based on an extended five-orbital Hubbard model including long-range Coulomb interactions.Our results show that the stabilized magnetic structure evolves with increasing hole doping level.Namely,the stripe antiferromagnetic phase dominates at zero doping,while magnetic structures with more antiferromagnetic linking numbers such as the staggered tetramer,staggered trimer,and staggered dimer phases become energetically favorable as the hole density increases.At a certain doping level,energy degeneracy of different magnetic structures appears,indicating strong magnetic frustration and magnetic fluctuations in the system.We suggest that the magnetic competition induced by the hole doping may explain the fast decrease of the Neel temperature TNand the moderately suppressed magnetic moment in the hole doped Fe-pnicitides.Moreover,our results show a sign reversal of the kinetic energy anisotropy as the magnetic ground state evolves,which may be the mechanism behind the puzzling sign reversal of the in-plane resistivity anisotropy in hole-doped Fe-pnicitides.展开更多
Dirac node-line(DNL) materials constitute a distinct category of topological semimetals, defined by the linear crossing of valence and conduction bands along one-dimensional lines within the Brillouin zone(BZ), resemb...Dirac node-line(DNL) materials constitute a distinct category of topological semimetals, defined by the linear crossing of valence and conduction bands along one-dimensional lines within the Brillouin zone(BZ), resembling the behavior of Dirac fermions. However, spin–orbit coupling(SOC) and electronic interactions can typically alter these intersections and break the DNLs. In mostly reported cases, DNLs are classified as non-interacting types, which highlights the significant research value in searching for robust interacting DNLs in practical materials. Here, by employing first-principles calculations that combine density functional theory(DFT) with dynamical mean-field theory(DMFT), and leveraging symmetry-based indicator theory, we identify CeAgSb_(2) as a Dirac semimetal. Our investigation reveals that robust Dirac nodal lines(DNLs)in this Kondo system are driven by Kondo interactions and nonsymmorphic lattice symmetries. Furthermore, our results demonstrate that the properties of these DNLs are substantially modulated by Kondo behavior across varying temperature regimes. The interacting DNLs in CeAgSb_(2) represents a rare example of Dirac semimetal under electronic correlations, and the peculiar variation of Dirac fermions with temperature provides theoretical reference for future experimental explorations of novel electronic-correlation effects in topological materials.展开更多
GeTe-based alloys are promising thermoelectric materials for use at medium temperatures owing to their excellent thermoelectric performance.In this study,Ge_(0.8-x)Mn_(0.1)Pb_(0.1)Sb_(x)Te alloys were obtained via vac...GeTe-based alloys are promising thermoelectric materials for use at medium temperatures owing to their excellent thermoelectric performance.In this study,Ge_(0.8-x)Mn_(0.1)Pb_(0.1)Sb_(x)Te alloys were obtained via vacuum melting and hot-press sintering.Sb doping effectively decreased the carrier concentration,resulting in an enhancement of the Seebeck coefficient and consequently imparting excellent electrical transport performance to the sample.With doping concentration increasing,the structure of the sample changed from rhombohedral to cubic,creating a more favorable band structure for electronic transport properties.The incorporation of Sb into GeTe intensifies the lattice defects within the material.The significant decrease in the lattice thermal conductivity of the Ge_(0.71)Mn_(0.1)Pb_(0.1)Sb_(0.09)Te alloy to 0.84 W m^(-1)K^(-1)at 323 K is primarily attributed to the phonon scattering effect emanating from the presence of edge dislocation,point defects,and inherent grain boundaries.Finally,the maximum ZT value of the Ge_(0.74)Mn_(0.1)Pb_(0.1)Sb_(0.06)Te alloy was~1.53773 K,which is a significant enhancement of 0.35 compared to the undoped Ge_(0.8)Mn_(0.1)Pb_(0.1)Te alloy.This substantial improvement underscores the positive impact of the selected doping elements and their concentrations on the overall thermoelectric performance of the alloy.展开更多
基金supported by the Natural Science Foundation of Guangxi Zhuang Autonomous Region(No.2023GXNSFBA026076)the Guangxi Key Laboratory of Optical and Electronic Materials and Devices(No.22KF-10)+1 种基金the Natural Science Foundation of China(Nos.21965009 and 22105048)the Guilin University of Technology Research Startup Project(No.GUTQDJJ2021073),and the Guangxi BaGui Scholars Special Funding.
文摘Bi_(1-x)Ho_(x)VO_(4)(0.1≤x≤0.9)ceramics were prepared via a solid-state reaction method,and all the ceram-ics could be well densified in the 920–980℃range.The ceramics with 0.1≤x<0.4 were composed of both monoclinic scheelite(M)and tetragonal zircon(T)phases,and a single M phase could be obtained in the range of x≥0.4.The measuredε_(r) decreased from 58.9(x=0.1)to 14.7(x=0.9),so do the calcu-lated values(ε_(r)(C−M)=34.3–12.1),and the main reason forε_(r)>ε_(r)(C−M)was the rattling of Ho^(3+)in the dodecahedron.Two points with zeroτf appeared in Bi1–x Hox VO4(0≤x≤1)ceramics,and the best mi-crowave dielectric properties withε_(r)=16.6,Q×f=18,400 GHz(f=10.69 GHz),andτf=+3.29 ppm/℃were obtained in the Bi_(0.2)Ho_(0.8)VO_(4)ceramic.The change in temperature coefficient of ionic polarizability(τ_(αm))caused by the rattling effect of cations is the physical essence that affectsτf.Therefore,the rattling effect can be used as an effective mechanism to regulateτf in low-ε_(r) materials.Furthermore,there was no chemical reaction between Bi_(1-x)Ho_(x)VO_(4) and Ag electrode,which indicates potential applications in low-temperature co-fired ceramic(LTCC)technology.
基金the Guangxi Natural Science Foundation,China(Grant Nos.2022GXNSFAA035560and GuikeAD20159009)the Scientific Research Foundation of Guilin University of Technology(Grant No.GLUTQD2017009)。
文摘The competition between different magnetic structures in hole-doped Fe-pnicitides is explored based on an extended five-orbital Hubbard model including long-range Coulomb interactions.Our results show that the stabilized magnetic structure evolves with increasing hole doping level.Namely,the stripe antiferromagnetic phase dominates at zero doping,while magnetic structures with more antiferromagnetic linking numbers such as the staggered tetramer,staggered trimer,and staggered dimer phases become energetically favorable as the hole density increases.At a certain doping level,energy degeneracy of different magnetic structures appears,indicating strong magnetic frustration and magnetic fluctuations in the system.We suggest that the magnetic competition induced by the hole doping may explain the fast decrease of the Neel temperature TNand the moderately suppressed magnetic moment in the hole doped Fe-pnicitides.Moreover,our results show a sign reversal of the kinetic energy anisotropy as the magnetic ground state evolves,which may be the mechanism behind the puzzling sign reversal of the in-plane resistivity anisotropy in hole-doped Fe-pnicitides.
基金Project supported by the National Natural Science Foundation of China (Grant No. 12364023)the Natural Science Foundation of Guangxi Zhuang Autonomous Regin, China (Grant No. 2024GXNSFAA010273)。
文摘Dirac node-line(DNL) materials constitute a distinct category of topological semimetals, defined by the linear crossing of valence and conduction bands along one-dimensional lines within the Brillouin zone(BZ), resembling the behavior of Dirac fermions. However, spin–orbit coupling(SOC) and electronic interactions can typically alter these intersections and break the DNLs. In mostly reported cases, DNLs are classified as non-interacting types, which highlights the significant research value in searching for robust interacting DNLs in practical materials. Here, by employing first-principles calculations that combine density functional theory(DFT) with dynamical mean-field theory(DMFT), and leveraging symmetry-based indicator theory, we identify CeAgSb_(2) as a Dirac semimetal. Our investigation reveals that robust Dirac nodal lines(DNLs)in this Kondo system are driven by Kondo interactions and nonsymmorphic lattice symmetries. Furthermore, our results demonstrate that the properties of these DNLs are substantially modulated by Kondo behavior across varying temperature regimes. The interacting DNLs in CeAgSb_(2) represents a rare example of Dirac semimetal under electronic correlations, and the peculiar variation of Dirac fermions with temperature provides theoretical reference for future experimental explorations of novel electronic-correlation effects in topological materials.
基金financially supported by the National Natural Science Foundation of China(Nos.12204355,52272210,12364006 and 12164011)the Open Project of State Key Laboratory of Superhard Materials,Jilin University(No.202110)the Natural Science Foundation of Shandong Province(Nos.ZR2022QA018,ZR2023QE282,ZR2023ME001 and ZR2023MF081)
文摘GeTe-based alloys are promising thermoelectric materials for use at medium temperatures owing to their excellent thermoelectric performance.In this study,Ge_(0.8-x)Mn_(0.1)Pb_(0.1)Sb_(x)Te alloys were obtained via vacuum melting and hot-press sintering.Sb doping effectively decreased the carrier concentration,resulting in an enhancement of the Seebeck coefficient and consequently imparting excellent electrical transport performance to the sample.With doping concentration increasing,the structure of the sample changed from rhombohedral to cubic,creating a more favorable band structure for electronic transport properties.The incorporation of Sb into GeTe intensifies the lattice defects within the material.The significant decrease in the lattice thermal conductivity of the Ge_(0.71)Mn_(0.1)Pb_(0.1)Sb_(0.09)Te alloy to 0.84 W m^(-1)K^(-1)at 323 K is primarily attributed to the phonon scattering effect emanating from the presence of edge dislocation,point defects,and inherent grain boundaries.Finally,the maximum ZT value of the Ge_(0.74)Mn_(0.1)Pb_(0.1)Sb_(0.06)Te alloy was~1.53773 K,which is a significant enhancement of 0.35 compared to the undoped Ge_(0.8)Mn_(0.1)Pb_(0.1)Te alloy.This substantial improvement underscores the positive impact of the selected doping elements and their concentrations on the overall thermoelectric performance of the alloy.
