熔体旋甩法合成n型(Bi_(0.85)Sb_(0.15))_2(Te_(1-x)Se_x)_3化合物的微结构及热电性能

采用熔体旋甩结合放电等离子烧结(MS-SPS)技术制备了单相n型四元(Bi0.85Sb0.15)2(Te1-xSex)3(x=0.15,0.17,0.19,0.21)化合物,并对所得样品的微结构和热电传输性能进行了系统研究.样品自由断裂面的场发射扫描电子显微镜及抛光面的背散射电子成分分析表明:块体材料晶粒细小,晶粒排列紧密,成分分布均匀且相结构单一,样品中存在大量10—100nm的层状结构.随着Se含量x的增加,样品的电导率和热导率逐渐增加,而Seebeck系数逐渐降低.相比商业应用的区熔材料,MS-SPS方法合成的高Se组成的样品均在425K后表现出更高的ZT值,其中(Bi0.85Sb0.15)2(Te0.83Se0.17)3样品具有最高的ZT值,在360K可达到0.96,并在320—500K均保持较高的ZT值,500K时其ZT值相比区熔材料提高了48%.此外,通过调节Se的含量,可以有效地调控材料的ZT峰值出现的温度段,这对多级或梯度热电器件的制备具有重要意义.     

Ⅰ型锗基笼合物Ba8Ga16-xSbxGe30的合成及热电性能

用高温熔融结合放电等离子烧结(SPS)方法合成了Sb掺杂的单相n型Ba8Ga16-xSbxGe30化合物,探索了Sb对Ga的取代对其热电性能的影响规律.研究结果表明随着Sb取代分数x的增加,Seebeck系数逐渐降低,Seebeck系数峰值对应的温度向低温方向偏移.电导率随着x的增加先增大后减小,当x=2时达到最大值.Sb取代Ga后对化合物的热性能有较大影响,其热导率和晶格热导率都有不同程度的降低.在所有n型Ba8Ga16-xSbxGe30化合物中,Ba8Ga14Sb2Ge30化合物的ZT值最大,在950 K左右其最大ZT值达1.1.     

Zn掺杂n型笼合物Ba8Ga16-2xZnxGe30+x的热电传输特性

用高温熔融结合放电等离子烧结法制备了Zn掺杂单相n型Ba8Ga16-2xZnxGe30 x笼合物,探索了Zn对Ga的取代对其热电传输特性的影响规律.研究结果表明,n型Ba8Ga16-2xZnxGe30 x化合物的电导率随着x的增加逐渐增大,Seebeck系数随着x的增加而逐渐减小.当Zn完全取代Ga时,Ba8Zn8Ge38化合物的电导率反而急剧下降,Seebeck系数显著增大.Ba8Ga16-2xZnxGe30 x化合物的载流子迁移率随着温度的升高而降低,当Zn掺杂后,化合物的载流子迁移率有一定的增加,随着x的增加而逐渐增大.Ba8Ga16-2xZnxGe30 x化合物的热导率和晶格热导率变化规律类似,随着x的增加先减小后增大.在所有n型Ba8Ga16-2xZnxGe30 x笼合物中,Ba8Ga8Zn4Ge34化合物的ZT值最大,在1000 K时其最大ZT值达0.85.     

I型锗基笼合物Ba8Ga16-xSbxGe30的合成及热电性能

用高温熔融结合放电等离子烧结（SPS）方法合成了Sb掺杂的单相n型Ba8Ga16-xSbxGe30化合物，探索了Sb对Ga的取代对其热电性能的影响规律．研究结果表明：随着Sb取代分数x的增加，Seebeck系数逐渐降低，Seebeck系数峰值对应的温度向低温方向偏移．电导率随着x的增加先增大后减小，当x=2时达到最大值．Sb取代Ga后对化合物的热性能有较大影响，其热导率和晶格热导率都有不同程度的降低．在所有n型Ba8Ga16-xSbxGe30化合物中，Ba8Ga14Sb2Ge30化合物的ZT值最大，在950K左右其最大ZY值达1．1．     

Zn掺杂P型Ba8Ga16ZnxGe30-x笼合物的合成及热电性能

用熔融法结合放电等离子烧结方法合成了Zn掺杂单相p型Ge基Ⅰ型笼合物Ba8Ga16ZnxGe30-x(x=3,4,5,6),探索Zn取代Ge对其热电性能的影响规律,结果表明:所制备的Ba8Ga16ZnxGe30-x化合物为p型传导,随Zn取代量x的增加,化合物室温载流子浓度Np逐渐增加,室温载流子迁移率μH和电导率逐渐降低.在所有试样中,Ba8Ga16Zn3Ge27化合物的Seebeck系数α在300—870K内始终最大,温度为300K时Seebeck系数为234μV/K,在700K附近达295μV/K.化合物的热导率随Zn取代量x的增加而降低.Ba8Ga16Zn3Ge27化合物在806K最大ZT值达0.38.     

Nd0.3Sr0.7Mn1-xCrxO3(0.01≤x≤0.15)的低温热导率研究

报道Nd0.3Sr0.7Mn1-xCrxO3(0.01≤x≤0.15)的热导率在10~300K温区内随温度和Cr含量的变化关系.在所测温区,随着Cr掺杂的增加,样品热导率值整体上逐渐减小,但在x=0.15时,出现反弹.热导率值在绝缘体-金属转变附近有很大提高,这个提高随Cr含量的增加逐渐被压制,直到x=0.15消失.分析指出热导率在绝缘体-金属转变附近的提高是由声子热导率和自旋相关热导率两部分贡献的;Cr掺杂通过电荷、晶格和自旋相互作用影响和制约了热导率随温度的变化.结果表明体系中自旋对热导率的调制作用是不可忽略的.     

机械合金化法制备Nb_3Al_(1-x)Si_x

采用机械合金化法制备了一系列的Nb_3Al_(1-x)Si_x(x=0~0.2)多晶样品,利用高能球磨机获得Nb(Al,Si)固溶体,然后在900℃的温度下烧结将固溶体转变为超导相.XRD测试结果表明,经3小时高能球磨后Al和Si固溶到Nb中形成Nb(Al,Si)固溶体,烧结后的样品具有较好的单相性,为A15型晶体结构,并且晶格随掺杂量的增加逐渐减小.磁性测量结果表明,纯样Nb3Al的Tc约为14K,随掺Si量的增加Tc逐渐减小.结合EDX分析,所有Nb_3Al_(1-x)Si_x样品的超导电性来源于A15相,但由于随掺杂量的增加样品中Al的含量逐渐减少导致了Tc逐渐减小.     

Cu掺杂AgSbTe2化合物的相稳定、晶体结构及热电性能

利用熔融快淬结合放电等离子烧结(SPS), 制备了Cu_xAg_1-xSbTe₂(x= 0---0.3)样品. 粉末X射线衍射(XRD)分析结果显示, SPS处理以前, 含Cu样品形成NaCl型结构的固溶体, 而未加入Cu的样品析出Ag₂Te第二相. 根据热分析和XRD测量结果, Cu的加入能够有效抑制Ag₂Te的析出, 但同时会在快淬样品中产生少量非晶相. 在温度升高到540 K左右时, 非晶相发生晶化, 形成Sb₇Te亚稳相, 并最终转变成Sb₂Te₃稳定相. 对快淬样品进行低温SPS快速处理后, x =0.1样品为面心立方结构的单相化合物, 但是x =0.2, 0.3的样品分别析出第二相Sb₇Te和Sb₂Te₃. 由于析出第二相, x=0.2, 0.3样品的电导率增大, Seebeck系数减小, 热导率相应升高, 综合热电性能降低. x=0.1单相样品的功率因子与文献报道的AgSbTe₂化合物相当. 元素替代的合金化效应 增强了Cu_0.1Ag_0.9SbTe₂化合物的声子散射, 有效降低了样品的热导率. 因此, 单相样品Cu_0.1Ag_0.9SbTe₂表现出较佳的热电性能, 在620 K时热电优值达到1.     

(1-x)(K0.5Na0.5)NbO3-xSrTiO3陶瓷的弛豫铁电性能

通过对(1-x)(K0.5Na0.5)NbO3-xSrTiO3(0≤x≤0.15)陶瓷的相组成、晶体结构和介电性能的研究发现,该陶瓷为单一的钙钛矿结构相.当x含量较小(x＜0.1)时为正交相结构,x≥0.1时转变为四方相结构.随着SrTiO3掺杂量的增加,样品的致密度增加,样品由正常铁电相逐渐向弥散铁电相转变,且相变温度明显下降,其相变峰的半高宽D和临界指数γ,随 x 的增加而增加.样品损耗ε″r(复介电常数虚部)随温度T的变化表明低温时弛豫极化损耗起主要作用,高温时漏导损耗起主要作用.同时介电常数实部ε′r随频率的变化显示(1-x)(K0.5Na0.5)NbO3-xSrTiO3弛豫为德拜弛豫.     

n型BayNixCo4-xSb12化合物的热电性能

系统地研究了Ba填充分数及Ni含量对n型BayNixCo4-xSb12(x=0—0.1,y=0—0.4)化合物热性能及电性能的影响规律.n型BayNixCo4-xSb12的热导率随Ba填充分数的增加而显著下降,当Ba填充分数为0.3时,热导率随Ni含量的增加而降低,在x=0.05时,热导率达到最小值,晶格热导率随Ni含量的增加单调降低.电子浓度和电导率随Ba填充分数及Ni含量的增加而增加,塞贝克系数则随Ba填充分数及Ni含量的增加而减小.对于Ba0.3Ni0.05Co3.95Sb12试样,得到了1.2最大 关键词： n型方钴矿 填充 置换 热电性能     

Enhancement of the thermoelectric power factor of MnSi1.7 film by modulation doping of Al and Cu

It is well known that aluminum (Al) and copper (Cu) are acceptor impurities with shallow- and deep-energy levels in silicon (Si), respectively. The thermoelectric power factor of Al and Cu codoped Si film is larger than that of only Al-doped Si film. In this report, the Al and Cu codoped Si layer, Si: (Al + Cu), is used as a barrier layer, while a higher manganese silicide (HMS, MnSi_1.7) layer is used as a well layer to enhance the power factor of MnSi_1.7 film. It is found that the Al and Cu modulation doped MnSi_1.7 film, Si: (Al + Cu)/MnSi_1.7, has a power factor almost two times larger than that of only Al modulation doped MnSi_1.7 film, Si: Al/MnSi_1.7. It is also found that an undoped Si spacer layer between the Si: (Al + Cu) barrier layer and the MnSi_1.7 well layer can enhance the power factor further. Finally, it is demonstrated that the MnSi_1.7 film with double Si barrier layers, Si: (Al + Cu)/MnSi_1.7/Si: (Al + Cu), has the highest power factor, 1423×10^?6 W/m?K² at 783 K, which is very close to that of MnSi_1.7 bulk material.     

Investigation on microstructures of MnSix thin films by Raman spectroscopy

In this paper, Raman spectroscopy is used to study the microstructures of MnSi_x thin films annealed at different temperatures. Two phases of Mn silicides, MnSi_1.73 and MnSi, are identified, and their Raman spectra are reported. Each phase of Mn silicides shows a set of three well‐defined peaks at about 300 cm⁻¹ in the spectrum, which could be used as fingerprints in identifying the formation of the Mn silicides. Compared with conventional X‐ray diffraction method, Raman spectroscopy is found to be more sensitive to investigate the microstructures of Mn silicides, especially at the initial stage of formation of the Mn silicides. Copyright © 2008 John Wiley & Sons, Ltd.     

Sn-based type-VIII single-crystal clathrates with a large figure of merit

Single-crystal samples of type-VIII Ba₈Ga_{16 - x}Cu_xSn₃₀ (x=0, 0.03, 0.06, 0.15) clathrates were prepared using the Sn-flux method. At room temperature the carrier density, n, is 3.5-5×10¹⁹ cm^-3 for all the samples, the carrier mobility, μ_H, increases to more than twice that of Ba₈Ga₁₆Sn₃₀ for all the Cu doping samples, and consequently the electrical conductivity is enhanced distinctly from 1.90×10⁴ S/m to 4.40×10⁴ S/m, with the Cu composition increasing from x=0 to x=0.15. The Seebeck coefficient, α , decreases slightly with the increases in Cu composition. The κ values are about 0.72 W/mK at 300 K and are almost invariant with temperature up to 500 K for the samples with x=0 and x=0.03. The lattice thermal conductivity, κ_L, decreases from 0.59 W/mK for x=0 to 0.50 W/mK for x=0.03 at 300 K. The figure of merit for x=0.03 reaches 1.35 at 540 K.     

非化学计量比AgSbTe2+x化合物制备及热电性能

采用高纯元素直接熔融、淬火并结合放电等离子烧结方法制备了非化学计量比AgSbTe_2+x(x=0—0.05)系列样品,研究了不同Te含量在300—600 K范围内对样品热电性能的影响规律.结果表明:随着Te含量的增加,Ag⁺离子空位浓度增加,空穴浓度和电导率大幅度提高,Seebeck系数减小.热导率随Te过量程度的增加略有增加,但所有Te过量样品的晶格热导率均介于0.32—0.49 W/mK之间,低于化学计量比样品的值,接近理论最低晶格热导率.AgS 关键词： 2')" href="#">AgSbTe₂ 非化学计量比 热电性能 热导率     

Effect of substitution of Ce on superconducting properties of Bi1.7Pb0.3Sr2Ca2−x Ce x Cu3O10+δ system

We have investigated the superconducting properties of the Bi_1.7 Pb_0.3Sr₂Ca_2−xCe _x Cu₃O_10+δ system with x=0.00, 0.02, 0.04, 0.08 and 0.1 by X-ray diffraction and magnetic susceptibility. The substitution of Ce for Ca has been found to drastically change the superconducting properties of the system. X-ray diffraction studies on these compounds indicate decrease in the c-parameter with increased substitution of Ce at Ca site and volume fraction of high T _c (2 : 2 : 2 : 3) phase decreases and low T _c phase increases. The magnetic susceptibility of this compound shows that the diamagnetic on set superconducting transition temperature (onset) varies from 109 K to 51 K for x=0.00, 0.02, 0.04, 0.08 and 0.1. These results suggest the possible existence of Ce in a tetravalent state rather than a trivalent state in this system; that is, Ca²⁺ → Ce⁴⁺ replacement changes the hole carrier concentration. Hole filling is the cause of lowering T _c of the system.     

Co掺杂Bi5Ti3FeO15多铁陶瓷的磁电性能

采用了传统的固相烧结工艺制备出Bi₅Fe_1-xCo _{x Ti3O15(BFCT-x,x=0.0—0.6)多铁陶瓷样品,研究了Co掺杂对Bi5FeTi3O15(BFTO)微观结构、铁电和磁性能的影响.X射线衍射谱显示样品均已形成四层铋系层状钙钛矿相,且随着掺杂量的增加发生了结构变化.拉曼光谱进一步证实掺入的Co占据了< 关键词： 固相烧结 多铁陶瓷 剩余磁化 剩余极化}     

p型Ag0.5(Pb8－xSnx)In0.5Te10化合物的制备及其热电性能

采用高温熔融缓冷和放电等离子烧结工艺制备了p型Ag_0.5(Pb_8-xSn_x)In_0.5Te₁₀五元化合物.研究了Sn含量对化合物载流子传输特性及热电性能的影响规律.结果表明：在Ag_0.5(Pb_8-xSn_x)In_0.5Te₁₀(x 关键词： 0.5(Pb_8-xSn_x)In_0.5Te₁₀')" href="#">Ag_0.5(Pb_8-xSn_x)In_0.5Te₁₀ 合成 载流子 热电性能     

Structure of precipitates and orientation relationships in Al,Ge, Mo-doped higher manganese silicide crystals

Abstract

The structure of Al, Ge, Mo-doped Higher Manganese Silicide (HMS) crystals with the general formulas Mn(Si_0.99Ge_0.01)_1.75, Mn(Si_0.995Ge_0.005)_1.75 and (Mn_0.98Mo_0.02)[(Si_0.98Ge_0.02)_1.75]_0.99Al_0.01 was investigated by scanning and transmission electron microscopy, electron diffraction and X-ray energy dispersive spectrometry in a wide scale range from a few mm to several Å. Several secondary phases were identified in the Mn₄Si₇ matrix: Ge_1?xSi_x (0.1 < x < 0.9) solid solution precipitates with Ge concentration ranging from 5 at. % up to 93 at.%, MoSi₂ platelets, MnSi and Mn₅Si₃ precipitates. Their morphology, structure and crystallographic relationships with the HMS matrix were determined. Mostly local strains in the matrix and precipitates due to lattice misfits at interfaces derived from crystallographic relationships were found two orders of magnitude higher than deformation induced by thermal expansion mismatch. Only a few exceptions of specific relationships were found when the lattice misfit and thermal mismatch have close values. The largest misfit of about 22% was observed between MnSi and Mn₄Si₇ what led to big and numerous cracks in crystals. Therefore, doping can improve the material performance (1) by preventing the formation of MnSi precipitates with metallic properties and (2) by reduction of cracking and crack propagation because of larger MnSi /Mn₄Si₇ lattice misfit compared to Ge_1?xSi_x /Mn₄Si₇ or MoSi₂/Mn₄Si₇ misfits.     

Solid-phase synthesis of manganese silicides on the Si(100)2 × 1 surface

The solid-phase synthesis of manganese silicides on the Si(100)2 × 1 surface coated at room temperature by a 2-nm-thick manganese film has been investigated using high-energy-resolution photoelectron spectroscopy with synchrotron radiation. The dynamics of variation of the phase composition and electronic structure of the near-surface region with increasing sample annealing temperature to 600°C, has been revealed. It has been shown that, under these conditions, a solid solution of silicon in manganese, metallic manganese monosilicide MnSi, and semiconductor silicide MnSi_1.7 are successively formed on the silicon surface. The films of both silicides are not continuous, with the fraction of the substrate surface occupied by them decreasing with increasing annealing temperature. The binding energies of the Si 2p and Mn 3p electrons in the compounds synthesized have been determined.     

Effect of La substitution on conductivity and dielectric properties of Bi1−xLaxFeO3 ceramics: An impedance spectroscopy analysis

Bismuth ferrite (BFO) and La-substituted BFO with composition Bi_1−xLa_xFeO₃ (x=0.05, 0.1 and 0.15) (BLFO_x=0.05-0.15) ceramics were prepared using the solid state reaction route. A structural phase transition from rhombohedral phase to triclinic phase was observed for BLFO_x=0.05-0.15 ceramics. Modulus spectroscopy reveals the deviation of dielectric behavior from ideal Debye characteristics and the dependence of conductivity on ion hopping in BFO and BLFO_x=0.05-0.15 ceramics. The conductivity of the BFO ceramics decreases for La content of 5 mol%, followed by a subsequent increase with 10 and 15 mol% of lanthanum doping. The typical values of the activation energies at high temperature reveal the contribution of short range movement of doubly ionized oxygen vacancies to the conduction process in BFO and BLFO_x=0.05 ceramics. Both short range and long range motion of oxygen vacancies are responsible for large conductivity in BLFO_{x=0.1 and 0.15} ceramics.