MoSi2—Mo5Si3复合材料的低温氧化行为

通过热重分析（TGA）、X射线衍射（XRD）和扫描电镜（SEM）研究了MoSi2-Mo5Si3复合材料的低温氧化行为,指出材料低温氧化时,随Mo5Si3量增多,材料氧化加剧,当Mo5Si3含量超过16％（质量分数）时发生“PEST”现象,所形成的SiO2由于MoS3晶须的大量存在,使其不能均匀连续地分布于材料表面,从而加剧了氧化。     

New fracture morphology of amorphous Fe78Si9B13 alloy

The tensile fracture morphology of a brittle amorphous Fe-based ribbon was investigated by scanning electron microscopy（SEM）. The fracture surface consists of mirror, mist and river-pattern zones with crack propagating. The formation of nanoscale damage cavity structure is a main characteristic morphology on the fracture surface. Approaching the fracture source in the mirror, these damage cavities assemble and form the nanoscale periodic striation patterns, which are neither Wallner lines nor crack front waves. At shear deformation stage, the apparent surface energy yf of amorphous Fe78Si9B13 ribbon is much smaller than that of less-brittle amorphous alloys, which indirectly indicates amorphous Fe7sSi9Bl3 ribbon is perfectly brittle. The crack branching appears at the moment of final fracture due to the high crack propagating velocity.     

New ternary aluminides T5M2Al having W5Si3-type structure

Six new ternary aluminides having W₅Si₃-type structure were found. These are: Zr₅Sn₂Al, Hf₅Sn₂Al, Ti₅Pb₂Al, Zr₅Pb₂Al, Hf₅Pb₂Al and Nb₅Sn₂Al.     

Low-temperature thermoelectric properties of α- and β-Zn4Sb3 bulk crystals prepared by a gradient freeze method and a spark plasma sintering method

The low temperature thermoelectric properties of Zn₄Sb₃ samples prepared by the gradient freeze (GF) method and sintering have been characterized. With decreasing temperature a dramatic rise in the thermal expansion is observed associated with the structural transition from β- to α-phase; Δl/l=2.8×10⁻⁴ at T_s^GF=257.4 K for GF and Δl/l=1.6×10⁻⁴ at T_s^S=236.5 K for sintered samples. Enhancement is observed in electrical conductivity and p-type thermopower at T_s^GF and T_s^S, while a reduction is observed in the magnetic susceptibility. The GF sample exhibits higher thermoelectric performance than the sintered sample. The power factor of the α-phase in the GF sample is twice as large as that of the β-phase; it exceeds 20 μW/cm·K² between 120 and 240 K, indicating that the α-phase Zn₄Sb₃ is one of the prime candidates for thermoelectric materials for cryogenic use.     

Mg2Si热电材料与Cu/Ni复合电极的接头界面及性能

为保证热连接过程中热电材料与导流电极之间实现良好连接,同时形成有效的阻隔界面防止界面元素扩散致使材料性能下降,本研究以Cu片作电极,引入中间层Ni箔作扩散阻挡层,采用电场激活压力辅助烧结(FAPAS)法,在合成高纯硅化镁(Mg_2Si)热电材料的同时,同步制得Cu/Ni/Mg_2Si热电接头。利用SEM、EDS以及XRD对接头界面的微观相组成、元素扩散特征以及新相生长规律进行了探讨,并且采用热震试验和四探针法对接头分别进行了力学性能和电传输性能的测试。结果表明,合成的Mg_2Si纯度高,高温热膨胀性能稳定;Ni层能有效阻隔界面元素扩散,与Mg_2Si实现良好的冶金结合,连接界面新相层的生成次序依次为Mg_2Si Ni3和Mg2Ni。Cu/Ni/Mg_2Si具有较好的热膨胀匹配性能,连接界面在持续60次的热震循环后依然保持完整。随着时效时间延长,界面扩散层增厚,接触电阻有所增大,与t~(1/2)具有近线性关系,且700℃下未时效的接头获得最小接触电阻率112μ?·cm~2。     

On the crystallographic characteristics of ion beam synthesised β–FeSi2

Nanometre-scale β–FeSi₂ precipitates were introduced in a single crystal silicon substrate by low-dose ion-beam synthesis (IBS). The crystallographic relationship between these nanometre β precipitates and the silicon substrate has been studied by high resolution electron microscopy (HREM). The results show that the orientation relationship (OR) between the nanometre β precipitates and the silicon substrate is [100]_β//[110]_Si and (001)_β//(1 1)_Si, with abnormally large strain between the precipitates and the substrate. This OR is important for the formation of 90°-OD boundaries within β–FeSi₂ grains. Also, the relationship between various reported low-index ORs has been analysed and a new low-index OR is predicted.     

Ordering in the sublattices of Fe3Al during the phase transformation B2↔D03

The temperature dependence of the iron concentrations in the individual sublattices of hyperstoichiometric binary Fe₇₂Al₂₈ and ternary Fe₆₈Al₂₈Cr₄ alloys were obtained from X-ray diffraction data measured in a high temperature vacuum chamber during linear heating around the phase transformation B2↔D0₃. A method for the processing of the diffraction pattern based on the splitting of the diffraction lines of the structure D0₃ into three groups is presented. Applying this method it was found that the structure B2 was not well developed in both samples. The maximum value of c_C≈0.8 gives S_B2 equal to 0.4 and 0.3 for binary and ternary alloy, respectively. The D0₃-order was not well developed too, because structure D0₃ arises from the structure B2. D0₃-ordering, i.e. redistribution of atoms within the sublattices A and B, is given only by the total number of iron atoms in these sublattices before the phase transformation B2↔D0₃.     

Fabrication and thermoelectric properties of crystal-aligned nano-structured Bi2Te3

With a view to experimental demonstration for an improved thermoelectric performance, a slip casting method under high magnetic field for uni-directionally aligned crystals has been investigated. The sintered body of Bi₂Te₃ powder, its size between 300 and 500 nm, green-bodied under 6 T magnetic field showed a 33% variation in the fraction of the directionally aligned crystals. According to increasing this fraction, electrical resistivity was reduced with keeping thermal conductivity and Seebeck coefficient unchanged. This could be explained from the fact that the aligned crystals by magnetic field has increased the carrier mobility keeping carrier concentration unchanged.     

Fe2O3对自保护药芯焊丝性能的影响

通过改变自保护药芯焊丝药芯中Fe2O3的加入量，系统地研究Fe2O3对预处理剂熔点、熔敷金属残留铝含量、焊缝的力学性能和断口的影响。结果表明，在一定范围内，随着药芯中Fe2O3含量的增加，预处理药粉的熔点增高，熔敷金属残留铝量减少，焊缝的抗拉强度和屈服强度下降而延伸率和低温冲击韧度提高，拉伸试棒的韧窝断口比例增加，夹杂物的尺寸和数量减少。焊缝中的夹杂物是由Ba、Ca、Al、Mg为主的复合夹杂物，形态以圆形和长形为主。但是，Fe2O3的加入量是有一定限制的，当Fe2O3的加入量大于焊丝总量的4．5％时，焊丝在焊接过程中对电弧电压十分敏感，甚至出现气孔。综合考虑焊接工艺性能和力学性能．药芯中Fe2O3的加入量应该占焊丝总重的2．5％～3．5％。     

Magnetic, electrical and plastic properties of Fe76Nb2Si13B9, Fe75Ag1Nb2Si13B9 and Fe75Cu1Nb2Si13B9 amorphous alloys

Influence of 1 h annealing in vacuum on magnetic, electrical and plastic properties of Fe₇₆Nb₂Si₁₃B₉, Fe₇₅Ag₁Nb₂Si₁₃B₉ and Fe₇₅Cu₁Nb₂Si₁₃B₉ melt spun ribbons were carefully investigated. It was shown that in all cases soft magnetic properties can be significantly enhanced by applying 1-h annealing at characteristic temperatures T_op. This optimization annealing causes that permeability increases more than 15-times and magnetic losses (tangent of loss angle) achieves a minimum in relation to the as quenched state. Using structural examinations (X-ray and HRTEM) it was shown that for the Fe₇₅Cu₁Nb₂Si₁₃B₉ alloy the optimized microstructure corresponds to a nanocrystalline αFe(Si) phase whereas in other alloys to a relaxed amorphous phase free of iron nanograins. As a consequence of this fact the Fe₇₆Nb₂Si₁₃B₉ and Fe₇₅Ag₁Nb₂Si₁₃B₉ alloys show higher plasticity in comparison to the nanocrystalline Fe₇₅Cu₁Nb₂Si₁₃B₉ alloy. Temperatures of the first stage of crystallization, and related diffusion parameters were determined using measurements of resistivity versus temperature with different heating rates.     

Microstructural behavior of the heat treated n-type 95% Bi2Te3-5% Bi2Se3 gas atomized thermoelectric powders

In this research, n-type 95% Bi₂Te₃-5% Bi₂Se₃ doped with 0.04% SbI₃ thermoelectric powders were manufactured by gas atomization process and subsequently, the effects of rapid solidification and heat treatment on the microstructure of the powder particles were investigated. The crystal structures were analyzed by X-ray diffraction (XRD) and cross-sectional microstructures were observed by the scanning electron microscopy (SEM). The rapidly solidified powders consist of homogeneously distributed needle shape intermetallic compounds. However, the size of the intermetallic compounds increased with the increasing powder size, whereas the oxygen content in the produced powder decreased. Heat treatment of the powders for various temperatures and periods showed a significant increase in the grain size resulting in a reduction in hardness. In addition, with the increasing heat treatment temperatures and periods, the orientation factor of the powder particles decreased, which is also evident in case of the reduction treated powders.     

Microstructural changes in particles detected during the transformation from β-FeOOH to α-Fe2O3 in dense aqueous suspensions

The hydrothermal transformation from β-FeOOH to α-Fe₂O₃ in dense aqueous suspensions, obtained by partial neutralization of concentrated FeCl₃ solution with concentrated NaOH solution, was investigated. Mössbauer spectroscopy was used for the phase analysis of samples, as well as the complementary techniques XRD and FT-IR. The size and morphology of the particles were inspected with FE-SEM. At the beginning of the crystallization process very fine β-FeOOH particles were formed, which transformed to α-Fe₂O₃ (end-product) with a prolonged time of heating. A small amount or traces of α-FeOOH as an intermediate phase were detected by FT-IR and FE-SEM. Gradual formation of α-Fe₂O₃ double spheres with ring was monitored. Double spheres with ring were formed by the aggregation mechanism. The orientation effect of α-Fe₂O₃ subunits in double spheres with ring was observed. α-Fe₂O₃ double spheres with ring also showed two narrow particle size distributions.     

Power factor of La1−xSrxFeO3 and LaFe1−yNiyO3

The electrical conductivity (σ), Seebeck coefficient (S), and power factor (σS²) of perovskite-type LaFeO₃, La_1−xSr_xFeO₃ [0.1 ≤ x ≤ 0.4] and LaFe_1−yNi_yO₃ [0.1 ≤ y ≤ 0.6] were investigated in the temperature range of 300–1100 K to explore their possibility as thermoelectric materials. The electrical conductivity of LaFeO₃ showed semiconducting behavior, and its Seebeck coefficient changed from positive to negative around 650 K with increasing temperature. The electrical conductivity of LaFeO₃ increased with the substitutions of Sr and Ni atoms, while its Seebeck coefficient decreased. The Seebeck coefficient of La_1−xSr_xFeO₃ was positive, whereas that of LaFe_1−yNi_yO₃ changed from positive to negative with increasing Ni content. The substitutions of Sr and Ni were effective in increasing the power factor of LaFeO₃; 0.0053 × 10⁻⁴ Wm⁻¹ K⁻² for LaFeO₃ (1050 K), 1.1 × 10⁻⁴ Wm⁻¹ K⁻² for La_1−xSr_xFeO₃ (x = 0.1 at 1100 K) and 0.63 × 10⁻⁴ Wm⁻¹ K⁻² for LaFe_1−yNi_yO₃ (y = 0.1 at 1100 K).     

Thermoelectric properties of Fe0.98Co0.02Si2 with ZrO2 and rare-earth oxide dispersion by mechanical alloying

The n-type Co-doped β-FeSi₂ (Fe_0.98Co_0.02Si₂) with dispersion of several oxides, such as ZrO₂ or several rare-earth oxides (Y₂O₃, Nd₂O₃, Sm₂O₃ and Gd₂O₃), was synthesized by mechanical alloying and subsequent hot pressing. The effects of these oxide dispersions on the thermoelectric properties of Fe_0.98Co_0.02Si₂ were investigated. ZrO₂ was decomposed in the β phase, and the ZrSi and -FeSi phases, which are metallic phases, were formed in the samples with ZrO₂ addition. The Seebeck coefficient and the electrical resistivity were significantly decreased with increasing amount of ZrO₂, indicating that a part of the Zr atoms was substituted for Fe atoms in the β phase. In the case of the samples with rare-earth oxide addition, a decomposition of a large amount of these added oxides did not occur. However, the rare-earth oxide addition caused a slight increase in the amount of the phase. The Seebeck coefficient was significantly enhanced by the rare-earth oxide addition especially in the low temperature range. These facts indicated that a small amount of rare-earth oxides was decomposed in the β phase, and rare-earth elements were substituted for Fe atoms as a p-type dopant, resulting in the decrease in the carrier concentration. The rare-earth oxide addition was also effective in reducing the thermal conductivity.     

Structure and unusual magnetic properties in the itinerant electron system Hf0.8Ta0.2(Fe1−xCox)2

The crystal structure and magnetization of Hf_0.8Ta_0.2(Fe_1−xCo_x)₂ are investigated by X-ray powder diffraction and magnetization measurements. The compounds exhibit the Laves C14 structure for x=0.0–0.2 and the C15 structure for x≥0.3. The structural transition from C14 to C15 leads to an anomaly of the unit cell volume between x=0.2 and 0.3. When x=0.0, the compound undergoes a magnetic phase transition from ferromagnetic to paramagnetic state via the antiferromagnetic state, in which a field-induced metamagnetic transition is observed. When x=0.1 and 0.2, the compounds exhibit unusually small saturation moments, which are considered as antiferromagnetism (with weak ferromagnetic impurities) and weak ferromagnetism or ferrimagnetism, respectively. The formation of the AFM state is associated with a small bond length of Fe atom in the 6h site. When x≥0.3, the compounds exhibit a ferromagnetic to paramagnetic transition, which can be explained by itinerant electron metamagnetism.     

Magnetic phase diagrams of the TbRh2−xPdxPdxSi2 and TbRu2−xPdxSi2 systems

The a.c. susceptibility and high field magnetization on TbRh_2−xPd_xPd_xSi₂ and TbRu_2−xPd_xSi₂ compounds were investigated up to 140 kOe. The (T,x) magnetic phase diagrams were determined. For both systems, an increase in the Pd content causes a decrease in the Néel temperature and changes the magnetization curves.     

Modification of primary Mg2Si in Mg-5Si alloys with Y2O3

The Y2O3 addition to Mg-5Si alloys has a good modification effect on the primary Mg2Si. With 0.05% or 0.1% （mass fraction） Y203 additions, the primary Mg2Si begins to change from coarse dendritic shape （about 100 μm） into small polyhedral shape and therefore the alloys exhibits sub-modified microstructure. With 0.2% Y2O3 addition, most of the primary Mg2Si becomes polyhedral shape and its average size is only 25 μm or less. The Mg-5Si alloy exhibits modified microstructure. In addition, the experiments show that the reaction between Mg and Y2O3 cannot occur in the sintered Mg-6Y2O3 compact; however, the reaction among Mg, Si and Y2O3 can occur in the sintered Mg-5Si-6Y2O3 compact. Apart from the adsorption and poisoning manners, other mechanisms may exist in the modification of Y2O3 addition on the primary Mg2Si.     

High temperature thermoelectric properties and energy transfer devices of Ca3Co4−xAgxO9 and Ca1−ySmyMnO3

The high temperature oxide thermoelectric materials of p-type Ca₃Co_4−xAg_xO₉ (denoted as p-Co349/Ag_x) and n-type Ca_1−ySm_yMnO₃ (denoted as n-Mn113/Sm_y) were prepared by the self-ignition method combined with a sintering technique. The influence of doping Ag and Sm on the thermoelectric properties of the corresponding materials was evaluated. The figures of merit, ZT, for the p-Co349/Ag_0.2 and n-Mn113/Sm_0.02 materials reached maxima of 0.20 and 0.15 at 973 K, respectively. The performances of thermoelectric devices constructed with the p- and n-type pairs were evaluated in terms of the maximum output power (P_max) and manufacturing factor. The P_max and volume power density for the four-leg devices reached 36.8 mW and 81.9 mW cm⁻³ at ΔT of 523 K, respectively.     

Temperature dependent conductivity and thermoelectric power of the iodine doped poly(vinyl alcohol)–Cu chelate

We have investigated the temperature dependence of electrical conductivity and thermoelectric power (TEP) at 1.7 K < T < 300 K in an organo metallic complex, the iodine doped poly(vinyl alcohol)–Cu²⁺ chelate. We observed intrinsic metallic temperature dependence of resistivity from room temperature to 68 K with a broad minimum [ρ(68 K)/ρ(300 K) 0.75], which has not been observed previously in similar organo metallic complexes. There occurs an unusual metal-insulator transition at T 68 K and the resisitivity increases upon cooling below 68 K. However, the low temperature resistivity becomes finite (instead of going to infinity), [ρ(1.7 K)/ρ(300 K) 0.98] indicating that a quantum mechanical tunneling conduction is dominant at this low temperature. It is remarkable that the resistivity at 1.7 K is as small as that of room temperature. Such unusual temperature dependence of conductivity could be understood as thermally assisted hopping conduction between metallic islands. However, the observed intrinsic metallic temperature dependence of resistivity implies that such hopping conduction barrier is not important at high temperature (T > 68 K). The intrinsic metallic characteristics are confirmed by the quasi-linear temperature dependence of TEP for the whole measured temperature range (1.7 K < T < 300 K) with a small slope change at low temperature, T < 68 K, which is understood as an effect of variable range hopping (VRH) conduction at low temperature. The results of magneto resistance (MR) and magneto thermoelectric power (MTEP) are consistent with the above interpretation.