Large Seebeck coefficients induced by high degeneracy of conduction band minimum,and low intrinsic lattice thermal conductivity originated from large lattice vibrational anharmonicity render Mg_(3)Sb_(2)as a promising...Large Seebeck coefficients induced by high degeneracy of conduction band minimum,and low intrinsic lattice thermal conductivity originated from large lattice vibrational anharmonicity render Mg_(3)Sb_(2)as a promising n-type thermoelectric material.Herein,we demonstrated unique concentration-dependent occupation behaviors of Cu in Mg_(3.4)Sb_(1.5)Bi_(0.49)Te_(0.01)matrix,evidenced by structural characterization and transport property measurements.It is found that Cu atoms prefer to enter the interstitial lattice sites in Mg_(3)Sb_(2)host with low doping level(Mg_(3.4)Sb_(1.5)Bi_(0.49)Te_(0.01)+x%Cu,x<0.3%),acting as donors for providing additional electrons without deteriorating the carrier mobility.When x is larger than 0.3%,the excessive Cu atoms are inclined to substitute Mg atoms,yielding acceptors to decrease the electron concentration.As a result,the electrical conductivity of the Mg_(3.4)Sb_(1.5)Bi_(0.49)Te_(0.01)+0.3%Cu sample reaches 2.3×10^(4)S/m at 300 K,increasing by 300%compared with that of the pristine sample.The figure of merit zT values in the whole measured temperature range are significantly improved by the synergetic improvement of power factor and reduction of thermal conductivity.An average zT∼1.07 from 323 K to 773 K has been achieved for the Mg_(3.4)Sb_(1.5)Bi_(0.49)Te_(0.01)+0.3%Cu sample,which is about 30%higher than that of the Mg_(3.4)Sb_(1.5)Bi_(0.49)Te_(0.01) sample.展开更多
To achieve a better material for uncooled infrared (IR) detector, polycrystalline VO2(B) thin films with layered W-doping were fabricated on Si substrates by magnetron sputtering, and the best temperature coefficient ...To achieve a better material for uncooled infrared (IR) detector, polycrystalline VO2(B) thin films with layered W-doping were fabricated on Si substrates by magnetron sputtering, and the best temperature coefficient of resistance (TCR) value reached -4.1%/K. The film synthesis was in a two-step route, first deposition at room temperature and then post-deposition annealing at 450 ℃, to better control the crystallization behavior. Various transmission electron microscopy (TEM) methods were employed to investigate three sets of multi-layered films with different deposition time, 10, 20, and 30 min, with especial emphasis on the effect of layered W-doping scheme on the formation of multiple VO2(B) layers. Spatial-resolved energy dispersive X-ray spectroscopy (EDS) revealed the alternative patterns of W-rich layers and W-poor layers, while the thinner films exhibited better crystallinity and texturing. By comparison with an as-deposited film, it was found that the inter-diffusion between the two types of layers was completed in the deposition step while both remained in amorphous structure. A stable W solution of about 8 cat% in VO2(B) layers measured from all these films indicated that the layered doping can tailor the multi-layered microstructure to optimize the performance of VO2(B) films.展开更多
Correlated phase and microstructural evolution are systematically investigated by electron microscopies in Sr-deficient Sr(Ti,Nb)O_(3)(STNO)thermoelectric ceramics incorporated with different fraction of reduced graph...Correlated phase and microstructural evolution are systematically investigated by electron microscopies in Sr-deficient Sr(Ti,Nb)O_(3)(STNO)thermoelectric ceramics incorporated with different fraction of reduced graphene oxide(RGO).It is found that while no impurity except for very few Ti_(3)O_(5) precipitates are observed in monolithic STNO,the Nb-enriched rutile TiO_(2) appears in RGO/STNO composites.With increasing RGO content,the amount of precipitates increase at first and then decrease when RGO content becomes high,which can be ascribed to the formation of local Magneli phase.In addition,the energy-dispersive X-ray spectra combined with cathodoluminescence characterization indicates that the variation of Sr deficiency experiences the opposite trend with respect to the precipitates content.These findings clearly reveal the unique reducing effect of RGO on the microstructure of doped SrTiO_(3) with Sr deficiency,which can greatly facilitate the design of perovskite based thermoelectric materials of hierarchical structure.展开更多
The A2B2O7 series of ternary oxides are derivatives of fluorite structure over a wide range of rA/rB.Competing by two rare-earths the A-site,La2-xLuxZr2O7 ceramics were found transparent only in pore-free microstructu...The A2B2O7 series of ternary oxides are derivatives of fluorite structure over a wide range of rA/rB.Competing by two rare-earths the A-site,La2-xLuxZr2O7 ceramics were found transparent only in pore-free microstructures with similar grain sizes of pyrochlore(PY)and defective fluorite(DF)phases.Mutual solubilities of Lu and La in both phases were found by imaging and energy-dispersive spectroscopy analysis in scanning electron microscope.The dual-phase microstructures were developed with liquid-phase resulted from the exothermal reactions,creating a miscibility gap between two structures to moderate their competing grain growth.Change in grain growth behaviors in liquid-phase is described by a nucleation line in La2Zr2O7-Lu2Zr2O7 phase diagram.Variations of solution levels in DF grains and co-existing of dual-phase grain clusters in common orientation were revealed in transparent ceramics by electron backscattered diffraction,resulted by epitaxial relation of two phases promoted by the liquid-phase.Oxygen vacancies and various hole states common in both phases were revealed by characteristic cathodoluminescence peaks.The collective effects of pores,phase and grain boundaries,oxygen vacancies on scattering or absorption of visible light enables to establish a hierarchical microstructure-transparency relationship in such complex oxide ceramics,which could be tailored or further optimized by controllable sintering.展开更多
To achieve a better material for thermoelectric power generation device, filled skutterudite Yb0.3 Co_4 Sb_(12) samples were fabricated by melting-quenching-annealing-spark plasma sintering(SPS)method. Two sets of sam...To achieve a better material for thermoelectric power generation device, filled skutterudite Yb0.3 Co_4 Sb_(12) samples were fabricated by melting-quenching-annealing-spark plasma sintering(SPS)method. Two sets of samples, before and after SPS, were investigated. In both the two sets of samples,the average grain size of the samples increases monotonously with the increase of annealing time,while Yb filling fraction firstly increases and then decreases. Yb not filling into the skutterudite remains at the grain boundaries in the form of Yb_2 O_3 after SPS, which could be quantified by the spatially difference method of energy dispersive spectra. Step distribution of Yb filling fraction was observed in the samples annealed for 1 h, which was caused by the microstructural evolution from the peritectic phases to the skutterudite phase. The sample annealed for 3 days and SPS sintered possesses the maximum value of Yb filling fraction 0.249 and the maximum ZT value of 1.24 at 850 K. These results are helpful to better understand the microstructural evolution and Yb filling behavior in skutterudite materials.展开更多
SrFBiS_(2) is a quaternary n-type semiconductor with rock-salt-type BiS_(2) and fluorite-type SrF layers alternately stacked along the c axis.The tunability of the crystal and electronic structures as well as the intr...SrFBiS_(2) is a quaternary n-type semiconductor with rock-salt-type BiS_(2) and fluorite-type SrF layers alternately stacked along the c axis.The tunability of the crystal and electronic structures as well as the intrinsically low thermal conductivity make this compound a promising parent material for thermo-electric applications.In the current work,we show that alloying of Se and S in SrFBi_(S) 2 reduces the optical band gap with the second conduction band serving as an electron-transport medium,simultaneously increasing the electron concentration and effective mass.In addition,the raw material Bi_(2)Se_(3) is shown to act as liquid adjuvant during the annealing process,favoring preferred-orientation grain growth and forming strengthen microstructural texturing in bulk samples after hot-pressed sintering.Highly ordered lamellar grains are stacked perpendicular to the pressure direction,leading to enhanced mobility along this direction.The synthetic effect results in a maximum power factor of 5.58 μm W cm^(-1) K^(-2) at 523 K for SrFBiSSe and a peak zT=0.34 at 773 K,enhancements of 180%compared with those of pristine SrFBiS_(2).展开更多
基金supported by the National Key Research and Development Program of China(Nos.2018YFA0702100 and 2019YFA0210001)National Natural Science Foundation of China(No.U21A2054 and 52072234)K.Guo acknowledges the support from Key Discipline of Materials Science and Engineering,Bureau of Education of Guangzhou(No.202255464)。
文摘Large Seebeck coefficients induced by high degeneracy of conduction band minimum,and low intrinsic lattice thermal conductivity originated from large lattice vibrational anharmonicity render Mg_(3)Sb_(2)as a promising n-type thermoelectric material.Herein,we demonstrated unique concentration-dependent occupation behaviors of Cu in Mg_(3.4)Sb_(1.5)Bi_(0.49)Te_(0.01)matrix,evidenced by structural characterization and transport property measurements.It is found that Cu atoms prefer to enter the interstitial lattice sites in Mg_(3)Sb_(2)host with low doping level(Mg_(3.4)Sb_(1.5)Bi_(0.49)Te_(0.01)+x%Cu,x<0.3%),acting as donors for providing additional electrons without deteriorating the carrier mobility.When x is larger than 0.3%,the excessive Cu atoms are inclined to substitute Mg atoms,yielding acceptors to decrease the electron concentration.As a result,the electrical conductivity of the Mg_(3.4)Sb_(1.5)Bi_(0.49)Te_(0.01)+0.3%Cu sample reaches 2.3×10^(4)S/m at 300 K,increasing by 300%compared with that of the pristine sample.The figure of merit zT values in the whole measured temperature range are significantly improved by the synergetic improvement of power factor and reduction of thermal conductivity.An average zT∼1.07 from 323 K to 773 K has been achieved for the Mg_(3.4)Sb_(1.5)Bi_(0.49)Te_(0.01)+0.3%Cu sample,which is about 30%higher than that of the Mg_(3.4)Sb_(1.5)Bi_(0.49)Te_(0.01) sample.
基金This work was financially supported by the National Natural Science Foundation of China under Grant Nos. 51532006 and 51325203, Shanghai Municipal Science and Technology Commission of Shanghai Municipality under Grant No. 16DZ2260600, and the 111 Project (D16002). We are grateful to the Shanghai Institute of Ceramics for technical assistance in TEM and SEM experiments, as well as to Prof. R. Huang of East China Normal University for TEM specimen preparations
文摘To achieve a better material for uncooled infrared (IR) detector, polycrystalline VO2(B) thin films with layered W-doping were fabricated on Si substrates by magnetron sputtering, and the best temperature coefficient of resistance (TCR) value reached -4.1%/K. The film synthesis was in a two-step route, first deposition at room temperature and then post-deposition annealing at 450 ℃, to better control the crystallization behavior. Various transmission electron microscopy (TEM) methods were employed to investigate three sets of multi-layered films with different deposition time, 10, 20, and 30 min, with especial emphasis on the effect of layered W-doping scheme on the formation of multiple VO2(B) layers. Spatial-resolved energy dispersive X-ray spectroscopy (EDS) revealed the alternative patterns of W-rich layers and W-poor layers, while the thinner films exhibited better crystallinity and texturing. By comparison with an as-deposited film, it was found that the inter-diffusion between the two types of layers was completed in the deposition step while both remained in amorphous structure. A stable W solution of about 8 cat% in VO2(B) layers measured from all these films indicated that the layered doping can tailor the multi-layered microstructure to optimize the performance of VO2(B) films.
基金supported by the National Natural Science Foundation of China[Grant numbers 51532006,51432004]State Administration of Foreign Experts Affairs of China,111 project[Grant number D16002]the Opening Project of Key Laboratory of Inorganic Functional Materials and Devices,Chinese Academy of Sciences(Grant number KLIFMD201804).
文摘Correlated phase and microstructural evolution are systematically investigated by electron microscopies in Sr-deficient Sr(Ti,Nb)O_(3)(STNO)thermoelectric ceramics incorporated with different fraction of reduced graphene oxide(RGO).It is found that while no impurity except for very few Ti_(3)O_(5) precipitates are observed in monolithic STNO,the Nb-enriched rutile TiO_(2) appears in RGO/STNO composites.With increasing RGO content,the amount of precipitates increase at first and then decrease when RGO content becomes high,which can be ascribed to the formation of local Magneli phase.In addition,the energy-dispersive X-ray spectra combined with cathodoluminescence characterization indicates that the variation of Sr deficiency experiences the opposite trend with respect to the precipitates content.These findings clearly reveal the unique reducing effect of RGO on the microstructure of doped SrTiO_(3) with Sr deficiency,which can greatly facilitate the design of perovskite based thermoelectric materials of hierarchical structure.
基金supported by the National Natural Science Foundation(Grant No.51532006)the National Bureau of Foreign Experts(111 Project No.D16002)。
文摘The A2B2O7 series of ternary oxides are derivatives of fluorite structure over a wide range of rA/rB.Competing by two rare-earths the A-site,La2-xLuxZr2O7 ceramics were found transparent only in pore-free microstructures with similar grain sizes of pyrochlore(PY)and defective fluorite(DF)phases.Mutual solubilities of Lu and La in both phases were found by imaging and energy-dispersive spectroscopy analysis in scanning electron microscope.The dual-phase microstructures were developed with liquid-phase resulted from the exothermal reactions,creating a miscibility gap between two structures to moderate their competing grain growth.Change in grain growth behaviors in liquid-phase is described by a nucleation line in La2Zr2O7-Lu2Zr2O7 phase diagram.Variations of solution levels in DF grains and co-existing of dual-phase grain clusters in common orientation were revealed in transparent ceramics by electron backscattered diffraction,resulted by epitaxial relation of two phases promoted by the liquid-phase.Oxygen vacancies and various hole states common in both phases were revealed by characteristic cathodoluminescence peaks.The collective effects of pores,phase and grain boundaries,oxygen vacancies on scattering or absorption of visible light enables to establish a hierarchical microstructure-transparency relationship in such complex oxide ceramics,which could be tailored or further optimized by controllable sintering.
基金financially supported by the National Natural Science Foundation of China under Grant Nos. 51532006 and 11704238Shanghai Municipal Science and Technology Commission of Shanghai Municipality under Grant No. 16DZ2260601State Administration of Foreign Experts Affairs of China 111 Project under Grant No. D16002
文摘To achieve a better material for thermoelectric power generation device, filled skutterudite Yb0.3 Co_4 Sb_(12) samples were fabricated by melting-quenching-annealing-spark plasma sintering(SPS)method. Two sets of samples, before and after SPS, were investigated. In both the two sets of samples,the average grain size of the samples increases monotonously with the increase of annealing time,while Yb filling fraction firstly increases and then decreases. Yb not filling into the skutterudite remains at the grain boundaries in the form of Yb_2 O_3 after SPS, which could be quantified by the spatially difference method of energy dispersive spectra. Step distribution of Yb filling fraction was observed in the samples annealed for 1 h, which was caused by the microstructural evolution from the peritectic phases to the skutterudite phase. The sample annealed for 3 days and SPS sintered possesses the maximum value of Yb filling fraction 0.249 and the maximum ZT value of 1.24 at 850 K. These results are helpful to better understand the microstructural evolution and Yb filling behavior in skutterudite materials.
基金This work was financially supported by the National Key Research and Development Program of China(2018YFA0702100)the National Natural Science Foundation of China(21771123,52072234)J.Zhang is grateful for the support by the Open Project of Jiangsu Key Laboratory for Carbon-Based Functional Materials&Devices(KJS2023).
文摘SrFBiS_(2) is a quaternary n-type semiconductor with rock-salt-type BiS_(2) and fluorite-type SrF layers alternately stacked along the c axis.The tunability of the crystal and electronic structures as well as the intrinsically low thermal conductivity make this compound a promising parent material for thermo-electric applications.In the current work,we show that alloying of Se and S in SrFBi_(S) 2 reduces the optical band gap with the second conduction band serving as an electron-transport medium,simultaneously increasing the electron concentration and effective mass.In addition,the raw material Bi_(2)Se_(3) is shown to act as liquid adjuvant during the annealing process,favoring preferred-orientation grain growth and forming strengthen microstructural texturing in bulk samples after hot-pressed sintering.Highly ordered lamellar grains are stacked perpendicular to the pressure direction,leading to enhanced mobility along this direction.The synthetic effect results in a maximum power factor of 5.58 μm W cm^(-1) K^(-2) at 523 K for SrFBiSSe and a peak zT=0.34 at 773 K,enhancements of 180%compared with those of pristine SrFBiS_(2).
