In our present work, the effect of the Zn-vacancy concentration on the lattice thermal conductivity of β-Zn4Sb3 at room temperature is studied by using the nonequilibrium molecular dynamics approach. Along both the x...
In our present work, the effect of the Zn-vacancy concentration on the lattice thermal conductivity of β-Zn4Sb3 at room temperature is studied by using the nonequilibrium molecular dynamics approach. Along both the x- and z- axes, the heat flux and the temperature gradient exponentially decay and increase respectively. The lattice thermal conductivity of the single crystal bulk β-Zn4Sb3 rapidly decreases when there exists Zn atom vacancy, and then the lattice thermal conductivity slowly falls further with the growing Zn atom vacancy proportion, which suggests that the Zn atom vacancy (nv) to the lattice thermal conductivity (kvac) leads to a scaling law of kv ∼ nv−α This phenomenon is attributed to the fact that the existence of vacancy scattering can significantly decrease the mean free path. When the vacancy proportion of Zn atom reaches 10%, that is the vacancy model of β-Zn4Sb3, the lattice thermal conductivity of β-Zn4Sb3 is 1.32 W/mk and 1.62 W/mk along the x- and z- axes respectively, which drops by ∼ 90% than that of its full occupancy model.
With good electrical properties and an inherently complex crystal structure, Cu2-xSe is a potential ＂phonon glass electron crystal＂ thermoelectric material that has previously not attracted much interest. In this st...
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With good electrical properties and an inherently complex crystal structure, Cu2-xSe is a potential ＂phonon glass electron crystal＂ thermoelectric material that has previously not attracted much interest. In this study, Cu2-xSe （0 ≤ x ≤0.25） compounds were synthesized by a melting-quenching method, and then sintered by spark plasma sintering to obtain bulk material. The effect of Cu content on the phase transition and thermoelectric properties of Cu2-xSe were investigated in the temperature range of 300 K-750 K. The results of X-ray diffraction at room temperature show that Cu2-xSe compounds possess a cubic structure with a space group of Fm3m （#225） when 0.15 〈 x ≤ 0.25, whereas they adopt a composite of monoclinic and cubic phases when 0 ≤x ≤ 0.15. The thermoelectric property measurements show that with increasing Cu content, the electrical conductivity decreases, the Seebeck coefficient increases and the thermal conductivity decreases. Due to the relatively good power factor and low thermal conductivity, the nearly stoichiometric Cu2Se compound achieves the highest ZT of 0.38 at 750 K. It is expected that the thermoelectric performance can be further optimized by doping appropriate elements and/or via a nanostructuring approach.
Cu-12 wt.%Al(Cu-12Al) alloy fabricated by continuous unidirectional solidification(CUS) process has high elasticity,high strength,high conductivity,high plasticity and other good comprehensive properties,which has a p...
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ISBN:
(纸本)9783037856093;3037856092
Cu-12 wt.%Al(Cu-12Al) alloy fabricated by continuous unidirectional solidification(CUS) process has high elasticity,high strength,high conductivity,high plasticity and other good comprehensive properties,which has a potential to develop into a high-performance elastic material as the alternative to beryllium ***,the room temperature tensile elongation of the columnar-grained structure(CGS) Cu-12Al alloy with high <001>β orientation along the axial direction exceeded 20%,which is six times more than that of the ordinary polycrystalline structure(OPS) Cu-12Al alloy(ε=2-4%) fabricated by traditional *** CGS Cu-12Al alloy shows lower flow stress and work-hardening rate during plastic deformation,which determines a dramatic improvement of workability comparing with the OPS *** the present paper,both the effects of the rolling process and its parameters on the microstructure and properties of the CGS Cu-12Al alloy sheets were *** results showed that the CGS sheets(σb=310 MPa,ε=19%) have the maximum reduction of 80% and remain columnar-grained structure after the first rolling pass at 700℃.After deformation the tensile strength was 401 MPa and the tensile elongation approached to 14%.Then,the hot rolled sheets were rolled again through the second pass at 325℃ and 700℃,*** maximum reduction of CGS sheets at 325℃ warm rolling was 20%,the sheets remain columnar-grained structure and β1'→α1' martensitic phase transformation occured;The second pass hot-rolling at 700℃ showed that the maximum reduction exceeded 60%,and the recrystallization occured in the *** two passes of hot-rolling(total deformation was 92%),although the recrystallization occured,the CGS sheets remained columnar-grained structure(CGS) high tensile elongation(8.3%),which is two times more than that of the as-cast OPS sheets,and is five times as much as the OPS sheets with the same total deformation.
The ZrB2/SiC/Zr2Al4C5 multi-phase ceramics were fabricated by spark plasma sintering (SPS) at 1800 °C for 3 min under 20 MPa in an vacuum. Oxidation behavior of multi-phase ceramics were investigated using thermo...
The ZrB2/SiC/Zr2Al4C5 multi-phase ceramics were fabricated by spark plasma sintering (SPS) at 1800 °C for 3 min under 20 MPa in an vacuum. Oxidation behavior of multi-phase ceramics were investigated using thermo gravimetric analysis (TGA) from 20 °C to 1500 °C and muffle furnace in stagnant air at 1200 °C. Samples were analyzed after oxidation by X-ray diffraction (XRD), scanning electron microscopy (SEM) along with energy dispersive spectroscopy (EDS) to determine the reaction products and to observe the microstructure. The results showed that the aluminium borate and mullite crystallize on the surface in the samples oxidized. The effect of Zr2Al4C5 content on the oxidation resistance of the ZrB2 ceramics were discussed respectively, and oxidation mechanism was also analysised.
BiOCl/BiOI nanocomposites were synthesized using a thermal impregnation method for the first time. The intense visible-light absorption and large specific surface area gave 4wt.% BiOCl/BiOI nanocomposites the best vis...
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BiOCl/BiOI nanocomposites were synthesized using a thermal impregnation method for the first time. The intense visible-light absorption and large specific surface area gave 4wt.% BiOCl/BiOI nanocomposites the best visible-light photocatalytic properties among all the catalysts for the photodegradation of methyl orange,about 78% after 2 h. But decreased activities were obtained with the increase of Bi OCl content in the nanocomposites. Considering the light absorption,specific surface area and the quantum efficiency, the high recombination of the photoinduced electron-hole pairs of the catalysts that lowed the quantum efficiency was believed to be the critical factor for their decreased photocatalytic activities.
Calcium fluoride nanoparticles with various amounts of erbium ion dopants were prepared by CTAB/C_4 H_9OH/C_7H_(16)/H_2O reverse micro-emulsion *** nanoparticles were studied by X-ray diffraction(XRD),transmission ele...
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Calcium fluoride nanoparticles with various amounts of erbium ion dopants were prepared by CTAB/C_4 H_9OH/C_7H_(16)/H_2O reverse micro-emulsion *** nanoparticles were studied by X-ray diffraction(XRD),transmission electron microscopy(TEM),fourier transform infrared spectroscopy(FTIR),absorption and fluorescence *** XRD patterns indicate a typical cubic fluorite structure and no other *** results show the synthesized particles having uniform grain size and without *** spectra reveal that there are some amounts of-OH,NO_3^-and other organic functional groups on the particle surfaces before the annealing *** absorption peaks and bands are present in the absorption spectra,corresponding to the rich energy levels of erbium *** Red-Shift of absorption bands and Blue-Shift of fluorescence peaks can be attributed to the weakened energy level split as a result of the decrease in crystal field strength.
Mg2Si and Mg2Sn are indirect band gap semiconductors with two low-lying conduction bands (the lower mass and higher mass bands) that have their respective band edges reversed in the two compounds. Consequently, for so...
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Mg2Si and Mg2Sn are indirect band gap semiconductors with two low-lying conduction bands (the lower mass and higher mass bands) that have their respective band edges reversed in the two compounds. Consequently, for some composition x, Mg2Si1−xSnx solid solutions must display a convergence in energy of the two conduction bands. Since Mg2Si1−xSnx solid solutions are among the most prospective of the novel thermoelectric materials, we aim on exploring the influence of such a band convergence (valley degeneracy) on the Seebeck coefficient and thermoelectric properties in a series of Mg2Si1−xSnx solid solutions uniformly doped with Sb. Transport measurements carried out from 4 to 800 K reveal a progressively increasing Seebeck coefficient that peaks at x=0.7. At this concentration the thermoelectric figure of merit ZT reaches exceptionally large values of 1.3 near 700 K. Our first principles calculations confirm that at the Sn content x≈0.7 the two conduction bands coincide in energy. We explain the high Seebeck coefficient and ZT values as originating from an enhanced density-of-states effective mass brought about by the increased valley degeneracy as the two conduction bands cross over. We corroborate the increase in the density-of-states effective mass by measurements of the low temperature specific heat. The research suggests that striving to achieve band degeneracy by means of compositional variations is an effective strategy for enhancing the thermoelectric properties of these materials.
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