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Ba₈Ga₁₆Zn_xGe_30-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Ba₈Ga₁₆Zn_xGe_30-x化合物为p型传导，随Zn取代量x关键词： p型笼合物 合成 热电性能     

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     

Cd掺杂p型Ge基Ba8Ga16CdxGe30-x Ⅰ型笼合物的结构及热电特性

以Cd作为掺杂元素,用熔融法结合放电等离子体烧结（SPS）技术制备了具有不同Cd含量的Ba₈Ga₁₆Cd_xGe_30-x（x=0.95, 1.00, 1.05, 1.10） Ⅰ型笼合物,研究了Cd掺杂对其结构及热电性能的影响.Rietveld结构解析表明所制备的Ba₈Ga₁₆Cd_xGe_{30- 关键词： p型笼合物 结构 热电性能}     

Effect of Sn-doping on the structural,magnetic and magnetocaloric properties of La0.67Ba0.33Mn1−xSnxO3 compounds

Magnetocaloric effect (MCE) in fine-grained perovskite manganites of the type La_0.67Ba_0.33Mn_1−xSn_xO₃ (x=0.05, 0.1 and 0.15) were prepared by the solid-state method. The prepared samples remain single phase and exhibit paramagnetic to ferromagnetic phase transition (T_C) at 340, 325 and 288 K for x=0.05, 0.1 and 0.15, respectively. From the measured magnetization data of La_0.67Ba_0.33Mn_1−xSn_xO₃ compounds as a function of field (2 T), the associated magnetic entropy change close to their respective Curie temperatures and the relative cooling power (RCP) have been determined. Large MCE has been obtained in all samples and |ΔS_M|_max reached the highest value of 2.49 J/kg K at T_C (288 K) for the sample x=0.15, with H=2 T.     

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Ba₈Ga_16-2xZn_xGe_30+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Ba₈Ga_16-2xZn_xGe_30+x化合物的电导率随着x的增加逐渐增 关键词： 热电传输性能 n型笼合物 框架取代     

Si含量对高锰硅化合物相组成及热电性能的影响研究

采用高频感应熔融、退火结合放电等离子烧结方法制备高锰硅(HMS)化合物MnSi1.70+x(x=0,0.05,0.1,0.15),系统研究了Si含量变化对材料相组成、微结构和热电性能的影响规律.结果表明,当x0.1时,样品由HMS和贫Si的MnSi金属相两相组成,随着Si含量x的增加,MnSi相相对含量减小;当x=0.1时,所得样品为单相HMS化合物;当x0.1时,样品由HMS和过量Si两相组成.随着x的增加,由于样品中高电导的金属相MnSi含量逐渐减少,样品的电导率逐渐下降,而Seebeck系数随之增加.室温下样品载流子浓度和有效质量随x增大逐渐减小,而迁移率逐渐增加.MnSi和Si杂相与HMS相比均为高热导相,因此当x=0.1时,由于样品为单相HMS,从而表现出最低热导率和最高ZT值.MnSi1.80样品在800K时热导率最小值达到2.25W·m-1K-1,并在850K处获得最大ZT值(0.45).     

熔体旋甩工艺对Zn掺杂Ⅰ-型Ba8Ga12Zn2Ge32笼合物微结构及热电性能的影响

采用新颖的熔体旋甩(MS)结合放电等离子烧结(SPS)技术制备了单相Zn掺杂的Ⅰ-型Ba₈Ga₁₂Zn₂Ge₃₂笼合物,研究了熔体旋甩工艺对其微结构以及热电性能的影响. 结果表明,MS得到的薄带自由面主要由300nm—1μm的小立方体单晶组成,薄带经SPS烧结后得到了具有大量层状精细结构的致密块体. 与熔融+SPS工艺制备的试样相比,熔融+MS+SPS制备的Ba₈Ga₁₂Zn 关键词： 熔体旋甩 Ⅰ-型笼合物 热电性能     

Sr掺杂钙钛矿型氧化物Y1-xSrxCoO3的溶胶-凝胶制备及电阻率温度关系研究

采用溶胶-凝胶方法成功制备了Sr的替代化合物Y_1-xSr_xCoO₃ (x=0, 0.01, 0.05, 0.10, 0.15, 0.20), 系统地研究了20–720 K温度范围内Y_1-xSr_xCoO₃的电阻率温度关系. 研究表明, 随着Sr的替代含量的增加, Y_1-xSr_xCoO₃的电阻率迅速地降低, 这主要是由于载流子浓度的增加引起. 样品x=0和0.01在低于330和260 K的温度范围内, 电阻率与温度之间满足指数关系lnρ∝1/T, 获得导电激活能分别为0.2950和0.1461 eV. 然而, 实验显示lnρ∝1/T关系仅成立于重掺杂样品的高温区; 在低温区莫特定律lnρ∝T^-1/4成立, 且表明重掺杂引入势垒, 导致大量局域态的形成. 根据莫特T^-1/4定律拟合实验数据, 评估了局域态密度N(E_F), 它随着掺杂量的增加而增加. 关键词： 热电材料 溶胶-凝胶 3')" href="#">YCoO₃     

Temperature and field dependence of the magnetic properties of Nd \mathsf{_{2-x}}Ce\mathsf{_{x}}CuO\mathsf{_4}

We have investigated the magnetic ordering of Nd_2-x Ce _x CuO₄ for x = 0, 0.09, 0.13, 0.15 and 0.18 by neutron diffraction at low temperatures down to 33 mK and under magnetic field up to 5 tesla applied along [1,-1,0] crystallographic direction. At zero applied magnetic field Cu magnetic sublattice orders at , 210, 130 and 105 K for x = 0, 0.09, 0.13, 0.15, respectively. No long range magnetic order of the Cu could be detected for x = 0.18. The magnetic order of Nd was found in all samples, with a gradual increase of the polarized magnetic moment with decreasing temperature, saturating around 1 K. Hyperfine induced nuclear polarization of the Nd nuclear spin has been observed below about 400 mK for samples with x = 0, 0.13, 0.15 and 0.18. Field variation of the intensities of the principal and superstructure reflections of Nd_2-x Ce _x CuO₄ at millikelvin temperatures shows a field-induced second-order double-k to single-k phase transition at H _c = 0.75 and 0.56 tesla for samples with x = 0 and 0.15, respectively at T = 50 mK. We have also investigated the polarization of the Nd electronic sublattice due to the field of the Cu sublattice by the element specific X-ray resonant magnetic scattering investigation with synchrotron radiation.Received: 9 April 2004, Published online: 14 December 2004PACS: 75.25. + z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source X-ray scattering, etc.)T. Chatterji: Has changed his surname from Chattopadhyay to Chatterji.     

Photoluminescence scanning on InAs/InGaAs quantum dot structures

The photoluminescence spectra of InAs quantum dots (QDs) embedded into four types of In_xGa_1−xAs/GaAs (x = 0.10, 0.15, 0.20 and 0.25) multi quantum well MBE structures have been investigated at 300 K in dependence on the QD position on the wafer. PL mapping was performed with 325 nm HeCd laser (35 mW) focused down to 200 μm (110 W/cm²) as the excitation source. The structures with x = 0.15 In/Ga composition in the In_xGa_1−xAs capping layer exhibited the maximum photoluminescence intensity. Strong inhomogeneity of the PL intensity is observed by mapping samples with the In/Ga composition of x ≥ 0.20-0.25. The reduction of the PL intensity is accompanied by a gradual “blue” shift of the luminescence maximum at 300 K as follows from the quantum dot PL mapping. The mechanism of this effect has been analyzed. PL peak shifts versus capping layer composition are discussed as well.     

Ga填充n型方钴矿化合物的结构及热电性能

用熔融退火结合放电等离子烧结(SPS)技术制备了具有不同Ga填充含量的Ga_xCo₄Sb₁₂方钴矿化合物,研究了不同Ga含量对其热电传输特性的影响规律. Rietveld结构解析表明,Ga占据晶体学2a空洞位置,Ga填充上限约为0.22,当Ga的名义组成x≤0.25时,样品的电导率、室温载流子浓度N_p随Ga含量的增加而增加,Seebeck系数随Ga含量的增加而减小. 室温下霍尔测试表明,每一个Ga授予框架0.9个电子,比Ga的氧化价态Ga³⁺小得多. 由于Ga离子半径相对较小,致使Ga填充方钴矿化合物的热导率κ及晶格热导率κ_L较其他元素填充的方钴矿化合物低. 当x＝0.22时对应的样品在300K时的热导率和晶格热导率分别为3.05Wm^-1·K^-1和 2.86Wm^-1·K^-1.在600K下Ga_0.22Co_4.0Sb_12.0样品晶格热导率达到最小,为1.83Wm^-1·K^-1,最大热电优值Z,在560K处达1.31×10^-3K^-1. 关键词： skutterudite化合物 Ga原子填充 结构 热电性能     

Structural, magnetic and magnetocaloric properties of La0.7−xEuxBa0.3MnO3 perovskites

Polycrystalline perovskite manganites La_0.7−xEu_xBa_0.3MnO₃(x=0.05, 0.1 and 0.15) were prepared by sol-gel method. The prepared samples remain single phase with a perovskite structure, revealed by X-ray diffraction. The structure refinement of La_0.7−xEu_xBa_0.3MnO₃(x=0.05, 0.1 and 0.15) samples was performed in the hexagonal setting of the R3¯c space group. The dependence of magnetization M on applied magnetic field H and temperature T was measured carefully near the Curie temperature T_C for all the samples. With the increasing Eu content, both the unit cell volume and Curie temperature T_C of 298 K has been detected with a maximum of magnetic entropy |ΔS_M^max| for the La_0.7−xEu_xBa_0.3MnO₃ with x=0.15, reaching a value of 2.3 J/kg K when a magnetic field of 10 kOe was applied and the relative cooling power (RCP) is 46 J/kg. These results suggest that the material may be a suitable candidate as working substance in magnetic refrigeration near room temperature.     

Magnetic properties and magnetic entropy change in Heusler alloys Ni50Mn35?xCuxSn15

The influence of Cu substitution for Mn on magnetic properties and magnetic entropy change has been investigated in Heusler alloys, Ni₅₀Mn_35−x Cu _x Sn₁₅ (x=2,5 and 10). With increasing Cu content from x=2 to x=5, the martensitic transition temperature, T _M , decreases from 220 K to 120 K. Further increasing Cu up to x=10 results in the disappearance of T _M . For samples Ni₅₀Mn₃₃Cu₂Sn₁₅ and Ni₅₀Mn₃₀Cu₅Sn₁₅, both martensitic and austenitic states exhibit ferromagnetic characteristics, but the magnetization of martensitic phase is notably lower than that of austenitic phase. The magnetization difference, ΔM, across the martensitic transition leads to a considerably large Zeeman energy, μ ₀ΔM⋅H, which drives a field-induced metamagnetic transition. Associated with the metamagnetic behavior, a large positive magnetic entropy change ΔS takes place around T _M . For the sample Ni₅₀Mn₃₃Cu₂Sn₁₅,ΔS reaches 13.5 J/kg⋅K under a magnetic field change from 0 to 5 T.     

Dielectric properties of epitaxial Pb1−x Sn x Te layers at microwave frequencies

The dielectric properties of epitaxial Pb_1−x Sn _x Te layers are investigated at 9 GHz in a composition range betweenx=0 and 0.225. The samples are characterized by fairly low carrier concentrations between 1.4×10¹⁶ and 32×10¹⁶ cm⁻³. Data of the static dielectric constant (ε ^s ) are obtained at temperatures of 77 and 300 K. The results of ε ^s are 25% to 100% higher compared to previous measurements in bulk material from other authors. The observed higher values of ε ^s in the investigated samples may be due to the reduced number of point defects in epitaxially grown Pb_1−x Sn _x Te layers. The model of Kawamura which predicts a dependence of ε ^s on the effective band gap cannot be verified.     

Phase transition and high temperature thermoelectric properties of copper selenide Cu2-x Se （0 ≤ x ≤ 0.25）

With good electrical properties and an inherently complex crystal structure, Cu_2-xSe is a potential “phonon glass electron crystal” thermoelectric material that has previously not attracted much interest. In this study, Cu_2-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 Cu_2-xSe were investigated in the temperature range of 300 K—750 K. The results of X-ray diffraction at room temperature show that Cu_2-xSe compounds possess a cubic structure with a space group of Fm3m (#225) when 0.15 < x le 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.     

Thermoelectric Properties of High-Entropy Wolframite Oxide: (CoCuNiFeZn)1−xGaxWO4

Herein, the synthesis of high-entropy wolframite oxide (CoCuNiFeZn)_1-xGaxWO₄ through standard solid-state route followed by spark plasma sintering and their structural, microstructural, and thermoelectric (TE) properties are investigated. X-ray diffraction pattern followed by patterns matching refinement shows a monoclinic structure with the volume of the unit cell decreasing with increasing Ga content. The optical bandgap for these oxides shows a cocktail effect in high-entropy configuration. The Seebeck coefficient indicates electrons as dominating charge carriers with a nondegenerate behavior. The electrical resistivity decreases with increasing temperature depicting a semiconducting nature. Thermal conductivity in high-entropy samples (κ ≈ 2.1 W m⁻¹ K⁻¹ @ 300 K) is significantly lower as compared to MgWO₄ (κ ≈ 11.5 W m⁻¹ K⁻¹ @ 300 K), which can be explained by the strong phonon scattering due to large lattice disorder in high-entropy configuration. The TE figure of merit zT increases with Ga doping via modifying all three TE parameters positively.     

Mössbauer study of tin-doped 1-2-3 and 2-1-4 highT c superconductors

Samples of YBa₂(Cu_0.85Sn_0.15)₃O_7–y (1-2-3), La₂(Cu_0.95Sn_0.05)O4_4–x, and La_1.85Ba_0.15(Cu_0.95Sn_0.05)O_4–x (2-1-4), with different oxygen stoichiometry, have been studied by Mössbauer spectroscopy. These measurements reveal the existence of two inequivalent sites for Sn in the (1-2-3) compounds. The (1-2-3) spectra display two quadrupole doublets which we associate with Sn in Cu(1) and Cu(2) sites, respectively. La compounds show a single quadrupole doublet.     

Investigation of p-type strained-layer InxGa1−xAs/AlyGa1−yAs quantum well infrared photodetectors for long wavelength infrared imaging arrays applications

Two p-type compressively strained-layer (PCSL) In_xGa_1−xAs/Al_yGa_1−yAs (where,x=0.4, 0.2;y=0, 0.15) quantum well infrared photodetectors (QWIPs) grown by MBE on (100) semi-insulating (SI) GaAs substrates have been investigated for 3-5 μm MWIR and 8-14 μm LWIR imaging arrays applications. The In_0.4Ga_0.6As/GaAs PCSL-QWIP utilizing the resonant transport mechanism between the heavy-hole type-I states and the light-hole type-II states shows a broadband double-peak response between 8 and 9 μm range. Using compressive-strain in the InGaAs quantum well, normal incident absorption was greatly enhanced by reducing the heavy-hole effective mass and increasing the density of states in the off-zone center. Maximum responsivities of 93 mA W⁻¹and 30 mA W⁻¹were obtained at peak wavelengths of λ_p1=8.9 μm and λ_p3=5.5 μm, respectively atV_b=1.6 V, and detectivity (D*) at λ_p1=8.9 μm was found to be 4.0×10⁹cm−√Hz/WatV_b=0.3 V andT=75 K for this QWIP. The In_0.2Ga_0.8As/Al_0.15Ga_0.85As PCSL-QWIP achieves two-color detection with peak wavelengths at 7.4 μm in the LWIR band and 5.5 μm in the MWIR band. This detector is under background limited performance (BLIP) atT=63 K for biases varying from −2.7 V to +3 V. A detectivity (D*) of 1.06×10¹⁰cm √Hz/Wwas obtained at λ_p7.4 μm,V_b1.0 V andT=81 K for this QWIP.     

Superconductivity at 40 K in La1.8Sr0.2CuO4

High-T _c superconductivity withT _c onsets up to 42 K (midpoint: 37 K, zero resistance: 34 K) is observed in X-rays homogeneous single phase La_1.8Sr_0.2CuO₄. The quarternary compounds La_2–x Ba _x CuO₄ and La_2–x Sr _x CuO₄ (0x0.3 for Ba and 0x<1 for Sr, depending on the heating conditions) are mixed-valence oxygen defect oxides, characterized by the presence of Cu²⁺ and Cu³⁺ simultaneously. These oxides have a tetragonal symmetry (space group:I 4/mmm) similar to that of K₂NiF₄. We report the synthesis, characterization, and superconducting properties of various high-temperature superconducting La–Ba–Cu–O and La–Sr–Cu–O compounds. Through the substitution of Sr for Ba in these oxygen defect compounds an increasing superconducting transition temperature onset from 28 K to 35 K for La_1.8Sr_0.1Ba_0.1CuO₄ was observed. A positive initial pressure coefficient ofdTc/dp=290 (mK/kbar) has been found for La_1.8Sr_0.2CuO₄ with a magnetic susceptibility change consistent with the 100% diamagnetic expectation value.     

激光光控超导YBa2Cu3Ox薄膜开关的研制

在对光控热电效应开关进行理论分析的基础上,木文提出用YBa₂Cu₃O_x薄膜制作光控开关,并测试了在液氮温度下薄膜开关在不同激光波长下的特征参数,测试的最好结果是响应度R_v(632.8nm,10kHz,1Hz)为217V/W,归一化探测率D_*(632.8nm,10kHz,1Hz)为2.3×10¹¹cm.Hz^1/2/W,响应时间τ为0.21ms.