Magnetocaloric effect of Pr2Fe17−x Mn x alloys

Polycrystalline Pr2Fe17-xMnx（x = 0, 1, and 2）alloys were studied by X-ray diffraction（XRD）, heat capacity, ac susceptibility, and isothermal magnetization measurements. All the alloys adopt the rhombohedral Th2Zn17-type structure. The Curie temperature increases from 283 K at x = 0 to 294 K at x = 1, and then decreases to 285 K at x = 2. The magnetic phase transition at the Curie temperature is a typical second-order paramagnetic–ferromagnetic transition. For an applied field change from0 to 5 T, the maximum-△SM for Pr2Fe17-xMnxalloys with x = 0, 1, and 2 are 5.66, 5.07, and 4.31 J·kg^-1·K^-1,respectively. The refrigerant capacity（RC） values range from 458 to 364 J·kg^-1, which is about 70 %–89 % that of Gd. The large, near room temperature △SM and RC values,chemical stability, and a high performance-to-cost ratio make Pr2Fe17-xMnxalloys be selectable materials for room temperature magnetic refrigeration applications.     

Ti50＋x Pd30Ni20—x合金的相变温度

使用热分析和高温X射线研究了Ti50-xPd30Ni20-x合金相变温度的变化情况,发现当Ti的原子分数偏离50%时,合金的相变温度随Ti成分的升高而降低,处于固溶处理的合金的相变温度最高,合金经过轧制及回复处理后,相变温度会降低。分析认为,这与合金内的缺陷、内应力和析出物密切相关。     

Magnetic-field-induced martensitic transformations in Ni47 − x Mn42 + x In11 alloys (with 0 ≤ x ≤ 2)

Magnetic properties and martensitic transformations in the Ni_{47 ? x} Mn_{42 + x} In₁₁ alloys (with 0 ≤ x ≤ 2) have been studied. The magnetic-field-induced martensitic transformation was found to be observed for all the alloys. The critical temperatures of magnetic and structural phase transformations, temperature dependences of spontaneous magnetization of austenite and martensite, and the critical field, at which the martensitic transformation occurs, have been determined based on magnetic measurements performed for the alloys under study. The spontaneous magnetization of the alloys in the martensitic state has been shown to be lower than that in the magnetic-field-induced austenitic state by a factor of six.     

TiMn2-5x(V4Fe)x(x=0.30, 0.35)贮氢合金结构与性能研究

用XRD、SEM等方法与手段,研究TiMn2-5x(V4Fe)x(x=0.30,0.35)贮氢合金的相结构及电化学性能。结果表明:主相为体心立方(bcc)结构的合金,其晶胞参数随x的增加而增大;SEM显示在基体中存在岛状结构,随着x的增加,岛状结构较基体的比率减少;电化学测试表明,x=0.35合金在常温下难以活化,加热到327K才能活化;而x=0.30合金常温下即可活化,该合金在充电过程中出现钝化,327K温度下钝化消除。比较合金在298K的PCT曲线,发现x=0.30合金的平台氢压约为0.2MPa,平台宽度较大,更有开发价值;同时计算x=0.30合金放氢过程的焓和熵,分别为–36.1kJ/mol,–126.9J/(mol·K)。     

The Heusler Phase Ti25(Fe50 − x Ni x )Al25 (0 ≤ x ≤ 50); Structure and Constitution

Alloys with composition Ti₂₅(Fe_50 − x Ni _x )Al₂₅ (0 ≤ x ≤ 50) were investigated employing electron probe microanalysis (EPMA) and X-ray powder diffraction (XPD). For TiFe₂Al, in situ neutron powder diffraction (ND) was used for the inspection of phase constitution covering the temperature range from 27 °C (300 K) to 1277 °C (1550 K). Combined Rietveld refinement of ND and XPD data for TiFe₂Al revealed that Fe atoms occupy the 8c site in space group Ti with a small amount of Al sharing the 4a site, and the remaining Ti and Al atoms adopting the 4b site. This structural model was successfully applied in the refinement of all alloys Ti₂₅(Fe_50 − x Ni _x )Al₂₅ (0 ≤ x ≤ 50). Partial atom order exists on the Fe-rich side while complete order is observed for the Ni-rich side. Profiles recorded by in situ neutron powder diffraction for TiFe₂Al in the range of investigated temperatures show two phases, namely Heusler phase and MgZn₂-type Laves phase. Diffraction peaks from the Heusler phase dominate the profiles at lower temperatures but at higher temperatures the MgZn₂-type Laves phase is the main phase. No CsCl-type phase was found in the alloy in the investigated temperature range. The thermal expansion coefficient of TiFe₂Al is 1.4552 × 10⁻⁵ K⁻¹.     

A Study of the Origin of Weak Ferromagnetism in Zn1−x Co x O

To study the origin of ferromagnetism in Zn_1?x Co _x O thin films, its thermal diffusivity, in addition to its magnetization measurements, were analyzed. Thin films of Zn_1?x Co _x O (x = 0.03) were deposited on Si (100) substrates through ultrasonic spray pyrolysis. Magnetization M(B) measurements at low temperature showed a hysteresis loop that indicated the existence of ferromagnetic ordering in Zn_0.97Co_0.03O. However, the magnetic moment per Co ion was much lower than expected. A comparison of M(T) measured at zero-field-cooled and field-cooled conditions showed a superparamagnetic-like behavior, with a blocking temperature of about 130 K. Temperature dependence on the thermal diffusivity of Zn_0.97Co_0.03O showed a pronounced lambda-shaped minimum at 130 K, which indicated the existence of a second-order phase transition at this temperature. The weak ferromagnetism in the Zn_0.97Co_0.03O with the Curie temperature of 130 K was ascribed to the uncompensated magnetic moment at the surface of CoO nanoclusters.     

Effect of La-Substitution on the Electrical Conductivity of Sr1−x La x MoO4+δ (x = 0-0.3) Compounds

Various compositions of Sr_1?x La _x MoO_4+δ (x = 0.05, 0.1, 0.2, and 0.3) compounds were prepared by solid state reaction route. The samples were characterized by powder-XRD, TG-DTA, and SEM-EDAX techniques. Formation of single crystalline phases of Sr_1?x La _x MoO_4+δ was confirmed from powder-XRD patterns. The thermal stability of La-doped SrMoO₄ compounds was investigated by TG-DTA. Uniform grain distribution was observed in the SEM image of 10-20 mol.% La-substituted compositions. Needle-shaped structures were observed in the SEM image of Sr_0.3La_0.1MoO_4+δ and were confirmed to be La₂Mo₂O₉ by XRD examination. The electrical conductivity of these compounds was measured by AC-impedance technique in the temperature range of 373-1073 K in air ambience and compared with that of pristine SrMoO₄. The electrical conductivity was found to decrease for La-substituted SrMoO₄ compared to pristine SrMoO₄. The diffusion coefficient calculated from the electrical conductivity was found to be in the range of 1.94 ± 0.02 × 10^?13 to 1.15 ± 0.01 × 10^?11 cm²/S at 873-1173 K for substituted composition and 3.47 ± 0.02 × 10^?13 to 2.48 ± 0.01 × 10^?10 cm²/S for pristine SrMoO₄ at 673-1073 K temperature range.     

Sm_（1＋x）Ba_（2－x）Cu_3O_y（0≤x≤0．4）的热力学稳定性

用测量固体电解质电池电动势（ＥＭＦ）的方法，测试了Ｓｍ－Ｂａ－Ｃｕ－Ｏ体系主要化合物的标准Ｇｉｂｂｓ生成自由能；结果发现，稀土复合氧化物Ｓｍ_（１＋ｘ）Ｂａ_（２－ｘ）Ｃｕ_３Ｏ_ｙ，随着固溶度ｘ增加，化合物稳定性下降ＤＴＡ实验支持这一结论。     

非晶薄膜的x光电子能谱

近年来,对非晶态合金的原子结构、电子输运、磁性、力学性能等都有很多工作,但对其内在的电子能态、光学特性等研究得尚少.大量的实验结果表明(除个别例外),稀土一Co和稀土Ni系非晶合金的磁有序转变温度都比其对应的晶态合金高;而稀土-Fe系的规律正与之相反.     

少量B_2O_3对（2x）B_2O_3·（50－x）PbO·（50－x）Bi_

通过传统熔体冷却方法确定了（２ｘ）Ｂ２Ｏ３·（５０－ｘ）ＰｂＯ·（５０－ｘ）Ｂｉ２Ｏ３（ｘ为摩尔分数）三元系统形成玻璃的最少Ｂ２Ｏ３引入量；利用ｘ射线衍射分析、红外光谱及密度测定等手段考察了（２ｘ）Ｂ２Ｏ３·（５０－Ｘ）ＰｂＯ·（５０－ｘ）Ｂｉ２Ｏ３二元系统（ｘ＝０）和三元系统（０＜ｘ＜７）物质的结构变化，初步探讨了少量Ｂ２Ｏ３的引入对该三元系统形成玻璃的作用。     

球磨Mg50Ni50＋x wt%Ti（x=0,1,3,5）合金的贮氢性能

为了改善镁基贮氢合金的贮氢性能,在合金中加入不同量的Ti作为催化剂,用机械球磨法制备出Mg50Ni50＋x wt%Ti（x=0,1,3,5）合金粉末。用XRD、SEM分析了合金的微观结构,研究了Ti含量的变化对合金气态吸氢动力学及电化学性能的影响。结果表明：随着Ti含量的增加,合金相中出现了TiNi2相,TiNi2相不利于气态吸氢及电化学贮氢性能,但对合金的容量保持率及高倍率放电性能有很好的促进作用。     

TEM analysis of Gd5(SixGel−x)4, where x=1/2

The material Gd₅(Si_xGe_l−x)4, with x=1/2 was investigated using transmission electron microscopy. The material possesses a complex crystallographic structure and undergoes a unique, reversible, transformation at low temperatures and an irreversible high temperature transformation. The high, room and low temperature microstructures of arc-melted and heat treated samples are reported. Direct observation of the transformation with a discussion on the mechanism of the reversible, low temperature, phase transformation is detailed.     

固相反应合成Sr_(1+x)Zr_4P_(6-2x)Si_(2x)O_(24)磷酸盐粉体

以SrCO_3、SiO_2、ZrO_2和(NH_4)H_2PO_4为实验原料,采用固相反应法制备出磷酸盐Sr_(1+x)Zr_4P_(6-2x)Si_(2x)O_(24)(x=0～0.4)粉体.XRD和SEM分析表明:在1100 ℃,4 h温度下煅烧能够合成单相Sr_(1+x)Zr_4P_(6-2x)Si_(2x)O_(24)(x=0～0.4)粉体,1100 ℃,4 h条件下制备的Sr_(1+x)Zr_4P_(6-2x)Si_(2x)O_(24)(x=0～0.4)粉体成球状,平均粒径在300～500 nm之间.在1100 ℃煅烧温度下适当延长保温时间,有利于Sr_(1+x)Zr_4P_(6-2x)Si_(2x)O_(24)(x=0～0.4)单相粉体的形成.     

Ag掺杂的赝两元合金（PbTe）1—x（SnTe）x热电性能

通过对Ag元素掺杂的赝两元合金（PbTe)1-x(SnTe)x(0≤x≤0.4）热电性能进行研究发展，处于本征态的PbTe合金电导率对掺杂较为敏感。但当摩尔分数增大时，赝两元合金（PbTe)1-x(SnTe)x电导率随掺杂量的增大受到抑制，这在高温情况下尤为显著。当温度低于约423K时，掺杂量对PbTe合金的Seebeck系数影响不大；但当温度大于423K时，PbTe合金的Seebeck系数随掺杂量而增大。掺杂量越大，摩尔分数越高，同一合金的Seebeck系数变化越小。热电优值计算表明，掺杂0.02mol%的合金系较适宜于制作成分递变的热电材料（FGM）。     

Crystal structures of PrAlxGe2−x compounds

The PrAl_xGe_2−x cross-section of the Pr–Al–Ge system at 1073 K was studied. The homogeneity ranges of two ternary praseodymium alumogermanides, PrAl_1.55–1.48Ge_0.45–0.52 and PrAl_1.42–0.98Ge_0.58–1.02, were determined and their crystal structures refined from X-ray single-crystal diffraction data. The former has a hexagonal structure of the AlB₂ type (hP3, P6/mmm, a=4.3223(3), c=4.2585(4) Å for x=1.476(2)) and the latter a tetragonal structure of the LaPtSi type (tI12, I4₁md, a=4.2534(5), c=14.641(2) Å for x=1). For both structures, the Al–Ge interatomic distances are close to the sum of the covalent radii, whereas the Pr–Al(Ge) distances agree well with the sum of the metallic radii. The solubility of Ge in the cubic Laves phase PrAl₂ was found to be less than 2 at.%, that of Al in off-stoichiometric PrGe_2−x less than 8 at.%. Al(Ge)-centered R₆ trigonal prisms constitute a common geometrical feature of the structures of the germanides RGe_2−x and alumogermanides RAl_xGe_2−x formed by the light rare-earth elements. Substitution of Ge for Al, or replacement of a large rare-earth element by a smaller one, leads to a reduction of the prism volume.     

x射线精确测定点阵常数专题总结

一.概况我们会同全国50多个单位完成五次多晶硅点阵常数精确测定。制订了用“X射线精确测定多晶硅点阵常数测试方法标准“草案”。并以“草案”为依据,对20个实验室衍射仪法及8个实验室的照相法的测试结果进行综合统计。     

Phase transformation behavior and mechanical properties of Ti50Ni49−x Fe1Co x shape memory alloys

In this article, the influence of Co addition on phase transformation behavior and mechanical properties of TiNiFe shape memory alloy was investigated extensively. Differential scanning calorimetry (DSC) measurements shows that martensitic start transformation temperatures (Ms ) decrease drastically with increasing Co content, while the R phase transformation start temperatures (Rs ) vary slightly. Nevertheless, the substitution of Ni with Co does not exert substantial influence on the two-stage transformation behavior of the TiNiFe alloy. The results from stress-strain curves indicate that higher critical stress for stress-induced martensitic transformation (rSIM ) has been obtained because of Co addition. In such cases, the Ti50Ni48Fe1 Co1.0 alloy maintains a good shape memory effect, and a maximum recoverable strain of 7.5 % can be obtained.     

A review of direct metamorphic In x Ga1− x As and InP epilayers on GaAs substrates by MOCVD

This is a review of direct growing high-quality In _x Ga_{1? x} As or InP buffer layers on GaAs substrates by metal-organic chemical vapour deposition (MOCVD). This low-temperature growth method benefits the improvement of metamorphic device performance. A simple and novel method of directly depositing thin In _x Ga_{1? x} As or InP buffer layers (<1?µm) on GaAs substrates is presented, instead of the strained-layer superlattice, two-step, graded or CS (compliant substrates) methods, while maintaining low dislocation density, high crystal quality, uniform and mirror-like surfaces. For the direct growth technique of In _x Ga_{1? x} As on GaAs, we found that an excellent quality In_0.54Ga_0.46As buffer of r.m.s surface roughness of only 0.686?nm by AFM and FWHM of 925 arcsec by XRD can be obtained at a low growth temperature of 440°C with a constant Ga/In_gas partial pressure of 5. An MIS-like Schottky diode with Au/i-InGaAs/n⁺-GaAs structure is investigated to check the film quality. A distinguished I–V characteristic with cut-in voltage of 0.23?V and reverse breakdown of 3?V, corresponding to the electric field of 2?×?10⁵?V?cm^?1, is also achieved. The superior results are mainly due to the use of low-temperature growth technology. In addition, we also found this growth technology is available to directly grow the InP buffer layers on GaAs. Experimental results conclude that the growth temperature of 480°C in harmony with the V/III ratio range of 130–210 is a suitable window to directly grow InP on GaAs substrates.

A review of direct metamorphic In _x Ga_{1? x} As and InP epilayers on GaAs substrates by MOCVD

All authors

Kao-Feng Yarn, Chin-I Liao & Chien-Lien Lin

https://doi.org/10.1080/08893110600664965

Published online:

25 January 2007

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