New TiNiSi-type RMgAg and RMgPd with R=Ca, Yb, and MgZn2-type Ca(Mg,Ag)2 compounds

The phases CaMgAg, YbMgAg, CaMgPd, and YbMgPd were synthesized by melting the constituent metals in sealed tantalum crucibles and by annealing at 1023 K. All the samples were homogeneous, and the crystallographic analysis, which was performed by powder and singlecrystal techniques, shows that the four compounds are isotypic and belong to the orthorhombic TiNiSi type. Magnetic measurements showed that YbMgAg and YbMgPd behave like Pauli paramagnets, according to the divalency of Yb in both phases. Within the Ca-Mg-Ag system, the existence range of the MgZn₂-type phases in the Mg-rich CaMg_2−x Ag _x pseudobinary system goes from CaMg₂ to CaMg_1.6Ag_0.4. Another stability region of the MgZn₂ structure occurs around the Ag-rich composition (Ca_0.94Mg_0.06)(Ag_1.60Mg_0.40), where magnesium replaces both the Ca and Ag atoms.     

First-principles investigations of structural,mechanical, electronic and optical properties of U3Si2-type AlSc2Si2 under high pressure

The structural, elastic, electronic and optical properties for U₃Si₂-type AlSc₂Si₂ compound under pressure were systematically investigated by using the first-principles calculations. The values of elastic constants and elastic moduli indicate that AlSc₂Si₂ keeps mechanical stability under high pressure. The mechanical properties of AlSc₂Si₂ are compared with those of Al₃Sc. The results indicate that AlSc₂Si₂ is harder than Al₃Sc. Anisotropic constant A^U and 3D curved surface of elastic moduli predict that AlSc₂Si₂ is obviously anisotropic under pressure. The electronic structure of AlSc₂Si₂ exhibits metallic character and the metallicity decreases with the elevated pressure. In addition, optical properties as a function of pressure were calculated and analyzed. The present work provides theoretical support for further experimental work and industrial applications.     

The homogeneity ranges of the L12-type intermetallic compounds Ni3Ga and Ni3Ge

The homogeneity ranges of the L1₂-ordered compounds Ni₃Ga and Ni₃Ge and the boundaries of the neighboring phases have been examined by electron probe microanalysis using heterophase alloys in the temperature ranges 1073 to 1373 K (Ni-Ga) and 1073 to 1346 K (Ni-Ge). The composition ranges of the L1₂-ordered phases have been found to be narrower than those reported in the literature, on the Ga-rich side for Ni₃Ga and on the Ge-deficient side for Ni₃Ge.     

New ternary compounds in the Lu-{Ru,Rh}-{Si,Ge} systems

Investigations made by powder X-ray diffraction on new ternary LuRuSi, Lu₂Ru₃Si₅, LuRu₂Si₂, LuRhSi, LuRh₂Si₂, LuRuGe, Lu₄Ru₇Ge₆, LuRhGe, Lu₄Rh₇Ge₆ and Lu₃Rh₄Ge₁₃ compounds are reported. The compounds LuRuSi (a=0.6823(1) nm, b=0.4188(1) nm, c=0.7151(1) nm), LuRhSi (a=0.6691(1) nm, b=0.4146(1) nm, c=0.7365(1) nm), LuRuGe (a=0.6871(1) nm, b=0.4259(1) nm, c=0.7305(1) nm) and LuRhGe (a=0.6736(1) nm, b=0.4216(1) nm, c=0.7493(1) nm) crystallize in the orthorhombic TiNiSi-type structure (space group Pnma). The Lu₂Ru₃Si₅ compound (a=1.0611(1) nm, c=0.5537(1) nm) crystallizes in the tetragonal Sc₂Fe₃Si₅-type structure (space group P4/mnc). The compounds LuRu₂Si₂ (a=0.4131(1) nm, c=0.9411(1) nm) and LuRh₂Si₂ (a=0.4005(1) nm, c=0.9830(2) nm) crystallize in the tetragonal CeGa₂Al₂-type structure (space group I4/mmm). The compounds Lu₄Ru₇Ge₆ (a=0.8239(1) nm) and Lu₄Rh₇Ge₆ (a=0.8244(1) nm) adopt the U₄Re₇Si₆-type structure (space group Im3m). The Lu₃Rh₄Ge₁₃ compound (a=0.8882(1) nm) belongs to the cubic Pr₃Rh₄Sn₁₃-type structure (space group Pm3n).     

SiCf/SiC复合材料表面Si/Yb2Si2O7双层涂层结合强度分析

目的 通过选择合适的复合材料拉伸方向和涂层制备工艺,在SiCf/SiC复材上获得高结合强度的Si/Yb2Si2O7双层涂层.方法 采用真空等离子喷涂技术在2.5D编织的SiCf/SiC复合材料表面制备Si涂层、Si/Yb2Si2O7双层涂层.采用金相、XRD、SEM和EDS对试样进行表征,采用拉伸试验测试涂层的结合强度...     

Electronic transport in Si and Ge polymers

Time-resolved transport studies which have now been carried out on a wide variety of alkyl- and aryl-substituted Si and Ge backbone polymers demonstrate the ability of these unipolar systems to transmit holes through the specimen bulk with negligible loss of these positive carriers to deep traps, making these materials attractive candidates for electronic device applications. Transport has been studied by measuring drift mobilities as a function of field, temperature and composition, using the small-signal time-of-flight technique. Transport occurs among chain backbone derived states, yet exhibits behavior essentially identical to systems in which transiting carriers are known to undergo thermally activated tunneling transitions among discrete molecular sites. On this basis it is suggested that disorder causes the chain backbone to be suborganized into domain-like units of varying conjugation length. The sensitivity of transport to large-scale thermodynamic processes, sidegroup substituent and effect of specific dopants is demonstrated.     

Si–Yb2O3/Yb2Si2O7/Yb2SiO5 EBC涂层组织结构及熔盐腐蚀行为研究

目的 研究Si–Yb₂O₃/Yb₂Si₂O₇/Yb₂Si O₅ 3层EBC涂层的抗熔盐腐蚀性能。方法 采用真空等离子喷涂工艺在试样表面单面制备Si–Yb₂O₃/Yb₂Si₂O₇/Yb₂Si O₅ 3层结构的EBC涂层,选用尺寸为Ф25 mm、厚度为5 mm的SiC_f/SiC复合材料基体试样,在900℃、NaCl(质量分数为50%)+Na₂SO₄(质量分数为50%)混合盐中进行连续100 h的熔盐腐蚀试验,采用光学显微镜、扫描电镜、X射线衍射仪等观察和测试3层EBC涂层熔盐腐蚀前后的形貌,分析其组织结构以及该EBC涂层在熔盐腐蚀过程中的化学反应机理。结果 经过连续100 h、900℃的熔盐腐蚀,基体SiC_f     

Magnetic,electronic and transport properties of RAg2Ge2 (R=Pr,Nd) compounds

Magnetization, magnetic susceptibility, electrical resistivity, thermoelectric power, neutron diffraction and X-Ray photoemission spectroscopy measurements were performed on polycrystalline samples of PrAg₂Ge₂ and NdAg₂Ge₂, both crystallizing with a tetragonal structure of the ThCr₂Si₂-type. The data indicate that both compounds order magnetically at low temperatures, PrAg₂Ge₂ at 12 K and NdAg₂Ge₂ at 2 K. Neutron diffraction data for the latter indicate antiferromagnetic collinear structure described by the propagation vector k=(½, 0, ½) at 1.5 K. Both compounds exhibit metallic-like electrical behavior. The X-Ray photoemission data indicate that the valence bands are formed mainly by the Ag 4d bands. The spin-orbit splitting values determined from the XPS spectra of Pr and Nd, 3d_5/2 and 3d_3/2, equal 20.5 eV for the Pr compound and 22.7 eV for the Nd compound. The analysis of these spectra performed on the basis of the Gunnarsson-Schönhammer model indicates a weak hybridization of the 4f electrons with the conduction band.     

Phase stability of the X2AlTi (X: Fe,Co, Ni and Cu) Heusler and B2-type intermetallic compounds

Ordering and phase separation between the B2 and L21 phases in the X2AlTi (X: Fe, Co, Ni, Cu) intermetallic compounds were investigated. The B2/L21 continuous ordering was determined using the diffusion couple technique in the temperature range of 1273–1573 K. It was found that the substitution of Co for Fe results in raising the B2/L21 ordering temperature and that of Cu for Ni brings about widening of the B2+L21 two-phase region on both the NiAl and NiTi sides. It is shown that the maximum temperatures of B2/L21 order–disorder transition (TcB2/L21max), the tricritical temperatures (TtB2/L21) and the phase boundaries of the miscibility gap between the B2 and L21 phases in the XAl–XTi pseudobinary systems can be well described by the 3d+4s electron concentration of the elements occupying the X site. On the basis of this finding, the phase stability and the interchange energies between Al and Ti in the next nearest neighbors of X–Al–Ti (X: Ti, V, Cr, Mn, Fe, Co, Ni and Cu) system are discussed.     

Electron microscopy examination of R5T4 alloys,where R = Ho,Yb and Gd,and T = Si,Ge, Ga and Sb

Optical and electron micrographs reveal that R₅(Si_xGe_1–x)₃-type compounds, existing as thin plates, are prevalent in R₅(Si_x,Ge_1–x)₄ compound systems. The purpose of this research is an attempt to improve understanding of the formation of these thin plates by extending microstructural examination to other R₅(Si_xGe_1–x)₄ systems where formation of R₅(Si_xGe_1–x)₃ compounds may face additional constraints. Ho₅(Si_0.8Ge_0.2)₄, Ho₅Ge₄, Yb₅Ge₄, Gd₅Ge_3.5Sb_0.5, Gd₅Ge₃Ga and Gd₅Ge₃Sn alloys were examined by X-ray powder diffraction, scanning and transmission electron microscopy and energy dispersive spectroscopy. R₅(Si_xGe_1–x)₃-type thin plates were observed in all alloys studied except for the Sb substituted system, which may be related to deviation of the valence electron concentration from normal R₅(Si_xGe_1–x)₄ systems. Calculations of lattice misfit based on various assumptions indicate that the formation of thin plates is less sensitive to small lattice distortion than initially believed, and also appears fairly insensitive to slight composition variations.     

快速凝固Gd5Si2Ge2合金的显微组织与相组成

研究了在真空电弧炉和快淬炉2种快速凝固条件下制备的Gd5Si2Ge2合金的显微组织与相组成。结果表明，Gd5Si2Ge2合金亿电弧炉熔炼条件下，具有不同质蟹的样品可以获得不同的显微组织与相组成。不同速度下，快淬甩带实验表明，在小于40m／s的快淬速度下，Gd5Si2Ge2合金为单斜Gd5Si2Ge2-型晶体结构：在50m／s的快淬速度下Gd5Si2Ge2合金包含Gd5Si4-型和Gd5Si2Ge2-型两相。证实了冷却速度对Gd5Si2Ge2合金的相组成有重要影响。     

Overview of magnetoelastic coupling in(Mn,Fe)_2(P,Si)-type magnetocaloric materials

(MnFe)_2(P, Si)-type compounds are, to date, one of the best candidates for magnetic refrigeration and energy conversion applications due to the combination of giant magnetocaloric effect (MCE), tunable working temperature range and low material cost. The giant MCE in the (Mn,Fe)_2(P, Si)-type compounds originates from strong magnetoelastic coupling, where the lattice degrees of freedom and spin degrees of freedom are efficiently coupled. The tunability of the phase transition, in terms of the critical temperature and the character of the phase transition, is essentially attributed to the changes in the magnetoelastic coupling in the (Mn, Fe)_2(P, Si)-type compounds. In this review, not only the fundamentals of the magnetoelastic coupling but also the related practical aspects such as magnetocaloric performance, hysteresis issue and mechanical stability are discussed for the (Mn, Fe)_2(P, Si)-type compounds. Additionally, some future fundamental studies on the MCE as well as possible ways of solving the hysteresis and fracture issues are proposed.     

MAXIMUM SOLUBILITY VARIATION OF Si, Ge, Sn OR Pb IN Ti

本文用统计分析的方法,研究了IVA族元素Si,Ge,Sn,Pb在α-Ti及β-Ti中的最大固溶度C_α,C_β的变化规律并建立了相应的方程式。研究结果表明,C_α和C_β的变化受本族元素的金属性(或非金属性)和原子半径差△r的控制,其中主要控制因素是金属性。金属性对C_β的影响大于对C_α的影响,而原子半径差对C_β的影响小于对C_α的影响。对Ti来说,上述基本规律具有一定的普遍意义。     

添加Si对A_2B_7型电极合金结构及电化学贮氢性能的影响(英文)

为改善La–Mg–Ni系A2B7型合金的电化学贮氢性能,在合金中添加一定量的Si元素,通过真空熔炼及退火处理的方法制备La0.8Mg0.2Ni3.3Co0.2Six(x=0-0.2)电极合金。研究Si元素的添加对合金结构及电化学贮氢性能的影响。结果表明,铸态及退火态合金均为多相结构,分别为Ce2Ni7型的(La,Mg)2Ni7相和CaCu5型的LaNi5相以及少量的残余相LaNi3。Si元素的添加没有改变合金的主相,但使得合金中的(La,Mg)2Ni7相减少而LaNi5相增加。添加Si显著地影响了合金的电化学性能。随着Si含量的增加,铸态及退火态合金的放电容量逐步降低,但循环稳定性却随着Si含量的增加而增强。此外,合金电极的高倍率放电性能、极限电流密度、氢扩散系数以及电化学交流阻抗谱的测试均表明合金的电化学动力学性能随着Si含量的增加先增加而后减小。     

Sn合金化对Gd5Si2Ge2磁致冷材料结构和性能的影响

以商业纯Gd为原料,采用非自耗电弧炉氩气保护下熔炼了Gd5Si2Ge2-xSnx(x=0.2,0.5,1)和Gd5Si2-yGe2Sny(y=0.1,0.2,0.5)系列合金,研究Sn合金化对Gd5Si2Ge2晶体结构和磁热性能的影响.粉末XRD结果表明Sn代Ge样品具有正交Gd5Si4型结构;Sn少量代Si(y=0.1,0.2)的样品具有单斜Gd5Si2Ge2型结构;Gd5Si1.5Ge2Sn0.5则为单斜和正交的混合结构.用超导量子磁强计(SQUID)测定了样品的M-T和不同温度的M-H曲线,结果表明Gd5Si2Ge2-xSnx(x=0.2,0.5,1)不具有巨磁热效应;Gd5Si1 9Ge2Sn01合金的最大磁熵变达15.3 J/kg·K(0 T～5 T),具有巨磁热效应.     

New ternary Yb5Sb3-type R5PtX2 compounds (R = Y,Gd and Er; X = Sb and Bi) and their magnetic properties

Six novel Yb₅Sb₃-type compounds (space group Pnma) have been synthesized: Y₅PtSb₂, Gd₅PtSb₂, Er₅PtSb₂, Y₅PtBi₂, Gd₅PtBi₂ and Er₅PtBi₂. The Gd₅PtSb₂, Gd₅PtBi₂, Er₅PtSb₂ and Er₅PtBi₂ undergo a ferromagnetic-type ordering followed by lower-temperature field sensitive magnetic transitions.     

红色荧光粉Ca_3Y_2Si_3O_(12):Eu~(3+)的制备及发光特性

采用高温固相法合成了红色荧光粉Ca_3Y_2Si_3O_(12):Eu~(3+)。研究了Eu~(3+)离子掺杂浓度、助熔剂及Gd~(3+)共掺杂对荧光粉发光特性的影响。XRD检测结果显示,荧光粉的主晶相为Ca_3Y_2Si_3O_(12),属单斜晶系。荧光光谱分析表明:硅酸盐荧光粉Ca_3Y_2Si_3O_(12):Eu~(3+)的发射光谱包含2个主峰,峰值分别位于590和614 nm,归属于Eu~(3+)离子从~5D_0→7~F_1和~7F_2的特征跃迁。用614 nm最强峰监测,得到激发光谱为一多峰宽带(200~500 nm)。改变Eu~(3+)离子掺杂浓度发现:随着掺杂量增加,荧光粉发光强度先增加后降低,最佳掺杂量为20 mol%;讨论了几种助熔剂的影响:NaCl、CaF_2作为助熔剂,对荧光粉的发光强度影响不大,H_3BO_3作为助熔剂降低荧光粉的发光强度,而NH_4F能显著提高荧光粉的发光强度;Gd~(3+)可以作为一种很好的共激活剂,敏化Eu~(3+)离子发光。     

Modification effect of Yb and Na_3PO_4 on microstructure of Mg_2Si/Mg-4Si alloy and mechanism

The modification effects of ytterbium(Yb), Na_3PO_4 and Yb + Na_3PO_4 on primary Mg_2Si phase in Mg-4Si alloys were investigated by means of X-ray diffraction(XRD), optical microscopy(OM), scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS) analysis in this work. The results indicate that the morphology of the primary Mg_2Si phase apparently changes from coarse dendrites to fine dispersive polygonal particles and the mean size decreases from 276.6 μm to 7.1 μm, with combined modification of 0.8wt.% Yb and 2.64 wt.% Na_3PO_4. Such a morphological evolution results in improvement in the ultimate tensile strength and elongation of the alloys as compared to the base alloy. This may be attributed to the formation of the YbP particles that acted as the heterogeneous nucleation substrates for the primary Mg_2Si particles, resulting in a refined distribution of these precipitates. The results of XRD examination show that there was no reaction between Si and Yb or Na_3PO_4. Solo addition of Yb or Na_3PO_4 into the melt has no real modification effect on the microstructure, but the primary Mg_2Si particles and α-Mg phases become coarser than that in the unmodified alloy.