纳米晶软磁复合磁粉芯在中高频段性能研究

介绍了利用球磨后的FeCuNbSiB合金粉末冷压制作纳米晶复合磁粉芯的工艺.探讨了粉末粒度为80～200目,绝缘剂量为1%～8%时纳米晶复合磁粉芯的频率特性,直流叠加特性及品质因数Q.制备出的平均粒度为80目的磁粉芯有效磁导率μe在1MHz范围内恒为85,在100kHz时其峰值Q为65,在f=50kHz,Bm=50mT测试条件下其损耗为102mW/cm3.其功率损耗比传统铁粉芯,Fe-Ni粉芯小.     

粉末挤出成型法制备FeCuNbSiB纳米晶磁粉芯

采用粉末挤出成型法制备了FeCuNbSiB纳米晶磁粉芯,并讨论了纳米晶粉体粒度对磁粉芯磁性能的影响。结果表明,粘结剂配方为硬脂酸1%、聚丙烯40%、石蜡59%采用粉末挤出成型法可以制备粉体与粘结剂比例为5∶1的FeCuNbSiB纳米晶磁粉芯;粉级搭配可提高磁粉芯密度,300、200与100目质量比为6∶3∶2的磁粉芯密度相对于300目FeCuNbSiB纳米晶磁粉芯提高了5%,达到了3.76g/cm2;200目FeCuNbSiB纳米晶粉为33%,180℃、1h热处理,磁粉芯有效磁导率μe为10.44、中心频率为600kHz、中心频率品质因数Q值为44。     

粉末挤出成型法制备FeSiAl/FeCuNbSiB磁粉芯

采用粉末挤出成型法制备了FeSiAl/Fe-CuNbSiB纳米晶磁粉芯,并讨论了FeSiAl粉复合量、粉胶质量比对磁粉芯磁性能的影响。结果表明粘结剂配方为硬脂酸1%、聚丙烯20%、石蜡79%,挤出成型粉胶质量比10∶1的FeSiAl/FeCuNbSiB纳米晶磁粉芯,磁粉芯密度达到4.69g/cm3。200目FeSiAl粉与300目FeCuNbSiB纳米晶粉复合,当磁粉芯磁粉质量配比为"200目FeSiAl粉30%+300目FeCuNbSiB纳米晶粉70%"、粉胶质量比为10∶1、44℃×0.5h石油醚脱脂、热处理温度160℃×1h时,磁粉芯取得最佳的软磁性能,磁粉芯中心频率f为600kHz,有效磁导率μe达到16.48,品质因数Q值为57.5;频率及温度的变化对磁粉芯的有效磁导率的影响小。     

TiB2与BN复相陶瓷的渗流模型

试验结果证实,TiB₂与BN复相陶瓷的导电性能符合渗流理论,原料粉粒度配比下,其渗流阀值为V_c%=22.9%;原料粉粒度比的改变将改变渗流阀值,从而改变各配比下的电阻率值;TiB₂与BN在SPS系统中快速烧结,晶粒的尺度比与原料粉的粒度比基本保持一致。     

原位生成Al2O3/Cu复合材料的新工艺

采用一种新型工艺制备了Al₂O₃/Cu复合材料。高能球磨制备亚稳态的Cu-0.8 wt% Al合金粉,再将Cu₂O粉与其一起进行高能球磨,然后将复合粉末压坯在真空炉中同时进行氧化和烧结。该工艺省略了还原剩余Cu₂O的环节,氧化和烧结时间仅为1 h。生成的Al₂O₃的粒径约250nm,颗粒间距约500 nm,均匀弥散分布;该材料冷加工后性能接近SCM制品性能。该配比的Al₂O₃/Cu复合材料的热稳定性良好,在800℃下循环冷淬20次无裂纹;软化温度为700℃。     

Fe/Fe_(73.5)Cu_1Nb_3Si_(13.5)B_9纳米晶磁粉芯研究

采用Fe粉复合FeCuNbSiB纳米晶粉体制备了磁粉芯,并讨论了退火温度、Fe粉复合量、纳米晶粉体粒度以及绝缘剂等对磁粉芯磁性能的影响.结果表明,在200～350℃和350～400℃内退火,随着温度的升高,μ_e均呈先增大后减小,375℃时达到最佳;当复合Fe粉后,发现其软磁性能得到了明显改善, Fe粉量为40%时,μ_e达到最大,且在100kHz～1MHz内,频率稳定性良好,其中心频率在500kHz附近,并随Fe粉量的增加而向低频发生偏移.纳米晶粉体的粒度越大,磁粉芯的磁性能越好;粉体粒度为100～200目时,其μ_e达到最大.当375℃退火,由有机绝缘剂、40%(质量分数)Fe粉、100～200目纳米晶粉制备的磁粉芯,其μ_e达52.72、损耗Pu为0.01317J/m~3、Bs为3.92×10~(-3)T、Br=6.48×10~(-5)T、H_c为1.28A/m.     

超临界流体干燥法制备TiO2/ Fe2O3 和TiO2/ Fe2O3/ SiO2 复合纳米粒子及光催化性能

以TiCl₄ 、Fe (NO₃ )₃·9H₂O 和Na₂SiO₃19H₂O 为原料, 采用溶胶凝胶法结合超临界流体干燥法(SCFD)制备了纳米级TiO₂/ Fe₂O₃ 和TiO₂/ Fe₂O₃/ SiO₂ 复合光催化剂。以光催化降解苯酚对所得催化剂的催化活性进行了评价。结果表明, 纳米TiO₂/ Fe₂O₃ 复合粒子与单组分TiO₂ 比较, 复合粒子光催化活性高于单组分的TiO₂, 6h 苯酚降解率高达95.9 %。SiO₂ 的加入可以抑制纳米粒子粒径的长大和晶相的转变, 增强TiO₂ 纳米粒子的热稳定性。复合光催化剂中Fe₂O₃ 最佳掺入量为0.06 %, SiO₂ 最佳掺入量为10 %(摩尔分数) 。并用XRD、TEM 和FTIR 等手段进行了表征。TiO₂ 以锐钛矿型形式存在, SiO₂ 以无定性形式存在。比较了不同制备方法制得的TiO₂/ Fe₂O₃ 复合光催化剂, 得出超临界干燥法制备的光催化剂具有粒径小、比表面积大、分散性好、光催化活性高等特点。采用超临界流体干燥可直接得锐钛型纳米复合光催化剂。     

纳米晶Fe73.5Cu1Nb3Si13.5B9磁粉芯的磁性能研究

利用球磨纳米晶Ｆｅ７３．５Ｃｕ１Ｎｂ３Ｓｉ１３．５Ｂ９合金得到的粉末压制成磁粉芯,研究其磁性。结果表明,在测量的频率范围内（１ｋＨｚ－１００ｋＨｚ）,该粉芯的磁导率几乎不随频率变化的而变化;粉芯的品质因数Ｑ随的增加而增加,在较高频率时有着比坡莫合金粉芯还要高的值,具有应用价值。推导出磁粉芯的静态磁导率的表达式发现分芯的磁导率与磁粉芯的密度有着密切的密度愈大,磁粉芯的静态磁导率愈高。     

γ-l2O3 纳米粉对氧化铝、碳化硅陶瓷纤维烧结特性的影响

研究了纳米γ-l₂O₃ 添加剂对氧化铝、碳化硅陶瓷纤维烧结特性和显微结构的影响。实验结果表明, 在纤维挤压成形过程中, 纳米γ-l₂O₃ 粉填充到微米氧化铝粉的孔隙之中, 提高了纤维的素坯密度, 当添加剂含量为40% 时, 纤维的素坯相对密度达到最大值。纳米γ-l₂O₃ 可以促进氧化铝和碳化硅纤维的烧结, 同时降低纤维的烧结温度, 提高纤维的密度。     

纳米Al2O3颗粒增强新型铜基自润滑复合材料

以Cu-Ni-Y₂O₃-MoS₂-Graphite混合粉为基体,加入质量分数分别为0%、1%、2%、3%、4%的纳米Al₂O₃增强相,采用粉末冶金方法制备纳米Al₂O₃增强新型铜基自润滑复合材料。结果表明：随着铜合金粉末中纳米Al₂O₃颗粒含量的增加 , 所制备自润滑复合材料样品的密度下降,但硬度和压溃强度先上升后下降,在Al₂O₃含量为2%时硬度从HV 23.7增加到HV 35.1,压溃强度从189 MPa提高到276 MPa。由石墨和MoS₂组成的混合固体自润滑材料的摩擦系数小且稳定,约0.12。Al₂O₃质量分数为2%的样品磨损量最小,是未加Al₂O₃试样磨损量的1/7～1/8。铜基体经过镍、纳米Al₂O₃等弥散颗粒强化和固体润滑相石墨和MoS₂的加入,所制备的材料已具有一定的自润滑性能。     

Chemical control of superconducting properties of (Y, Ca)(Sr, Ba)2Cu2.7Ga0.3O7?δ

The partial substitution of Ga at the Cu(1) (chain) sites of the YBa₂Cu₃O₇ structure allows synthesis at ambient pressure of Ba-free analogs, e.g., YSr₂Cu_2.7Ga_0.3O_7– . Materials with this composition have been found to be nonsuperconducting, but superconductivity has been induced by one or more of the following methods: Ca substitutions at the Y site; Ba substitutions at the Sr site; annealing in high-pressure oxygen. The influence of these chemical manipulations onT _c has been monitored and all methods have been found to enhanceT _c . The electronic effects of Ba substitutions have been deduced indirectly using powder neutron diffraction, and such substitutions appear to result in a redistribution of hole density into the Cu(1) sites from the superconducting CuO₂ planes.     

Microstructural study of YBa2Cu3O7/SrTiO3/YBa2Cu3O7 heteroepitaxial trilayer films grown on (100) SrTiO3 substrates

Detailed transmission electron microscopic study has been carried out on heteroepitaxial YBa₂Cu₃O₇/SrTiO₃/YBa₂Cu₃O₇ trilayer thin films grown on (100)SrTiO₃ substrates prepared by DC and RF magnetron sputtering. The microstructural results showed the existence of somea-axis-oriented YBCO grains 20–90 nm wide in thec-axis-oriented YBCO matrix. Some of thea-axis grains in the lower YBCO thin film layer have protruded into the above SrTiO₃ layer, which may cause short circuit between the two YBCO superconducting layers. This is unsuitable for the application of trilayer thin films for microelectronic devices. The defects on the surface of the substrates would also influence the growth quality of the YBCO thin films.     

First-principles study on electronic structure, phase stability, and optical properties of In2X2O7 (X═C, Si, Ge or Sn)

In₂Ge₂O₇ and In₂Si₂O₇ are commonly used as scintillation materials. More studies on In₂X₂O₇ (X═C, Si, Ge, or Sn) are important to explore the possibility of using these materials for optoelectronic devices. This work presents results dealing with structural properties, electronic structure, chemical bonding, carrier effective masses, and optical spectra of polymorphs of In₂X₂O₇ obtained from first-principles calculations. The monoclinic phase of In₂Ge₂O₇, cubic and monoclinic phases of In₂Si₂O₇, as well as cubic phase of In₂Sn₂O₇ are known in scientific literature. From the total energy calculations at high pressure/strain we have found that the monoclinic phase of In₂Si₂O₇, In₂Ge₂O₇, and In₂Sn₂O₇ can be transformed into the cubic phase. The cubic phase of In₂Ge₂O₇ and In₂Sn₂O₇ is found to be more stable than the monoclinic phase. However, the monoclinic phase of In₂C₂O₇ and In₂Si₂O₇ is more stable than the cubic phase. The phase stability study suggests that In₂C₂O₇ is not stable, and that it might dissociate into corresponding binary oxides. Effective masses of electrons and holes have been estimated. Analysis of optical properties shows that in Si solar cells In₂Si₂O₇ and In₂Sn₂O₇ can be used as antireflection coating layer.     

Structure and Superconducting Properties of Cd0.8Ba2(Y0.7Ca0.4)Cu3.5Oy

A new Cd-containing superconductor with nominal composition ofCd_0.8Ba₂(Y_0.7Ca_0.4)Cu_3.5O _y was synthesized and investigated. The obtained Cd and Ca-doped 123 phase exhibits an orthorhombic (T _c=80 K) or tetragonal (T _c=65 K) modification depending on the reaction atmosphere. It was shown that the combined Cd and Ca substitution facilitates the 123 phase formation. The results of the EDX analysis, as well as the comparison of the obtained lattice parameters with those of undoped, Cd-doped, and Ca-doped 123 have shown that both Cd and Ca enter the 123 phase and form a new Cd–Ba–Y–Ca–Cu–O superconducting compound.     

Two-gap superconductivity in R2Fe3Si5 (R=Lu,Sc) and Sc5Ir4Si10

R₂Fe₃Si₅ (R= Sc, Y, Lu) contains nonmagnetic iron and has a relatively high superconducting transition temperature T_c among iron-containing superconductors. An anomalous temperature dependence of specific heat C(T) has been reported for polycrystalline samples down to 1 K. We have grown R₂Fe₃Si₅ single crystals, confirmed the anomalous C(T) dependence, and found a second drop in specific heat below 1 K. In Lu₂Fe₃Si₅, we can reproduce C(T) below T_c, assuming two distinct energy gaps 2Δ ₁/k_BT_c = 4.4 and 2Δ ₂/k_BT_c = 1.1, with nearly equal weights, indicating that Lu₂Fe₃Si₅ is a two-gap superconductor similar to MgB₂. Hall coefficient measurements and band structure calculation also support the multiband contributions to the normal-state properties. The specific heat in the Sc₂Fe₃Si₅ single crystals also shows the two-gap feature. R₅Ir₄Si₁₀ (R = Sc, rare earth) is also a superconductor where competition between superconductivity and the charge-density wave is known for rare earths but not for Sc. We have performed detailed specific heat measurements on Sc₅Ir₄Si₁₀ single crystals and found that C(T) deviates slightly from the behavior expected for weak-coupling superconductors. C(T) for these superconductors can also be reproduced well by assuming two superconducting gaps.     

Some thermodynamic aspects of the high-temperature transition in doped V2O3

Measurements of the entropy change are reported for the high-temperature metal-insulator (MI) transitions in the (V_1–xCr_x)₂O₃ and (V_1–xAl_x)₂O₃ systems. It is emphasized that the entropy of the I phase exceeds that of the M phase. Evidence is presented to show that the M and I phases coexist over a narrow temperature range. The transformation is attended by enormous hysteresis effects; these indicate that the lattice plays an important role in the transition. The probable role of Cr³⁺ and Al³⁺ as a dopant in the V₂O₃ lattice is briefly discussed. A phase diagram for the dilute V₂O₃-Al₂O₃ alloy system is presented.     

Structural and magnetic study of nitrided Co74Fe8B12Si6 and Co74Fe4Mn4B12Si6 ribbons

The nitriding thermochemical treatment (NTT) is commonly used for steels. In this paper, the experimental conditions required for NTT, and the influence of such treatments on the structure and hysteresis loops of Co₇₄Fe₈B₁₂Si₆ and Co₇₄Fe₄Mn₄B₁₂Si₆ ribbons are reported. The results have been compared with those obtained with ribbons treated according to conventional thermal treatment (CTT) as well.     

Two-gap superconductivity in R2Fe3Si5 (R=Lu,Sc) and Sc5Ir4Si10

Abstract

R₂Fe₃Si₅ (R= Sc, Y, Lu) contains nonmagnetic iron and has a relatively high superconducting transition temperature T_c among iron-containing superconductors. An anomalous temperature dependence of specific heat C(T) has been reported for polycrystalline samples down to 1 K. We have grown R₂Fe₃Si₅ single crystals, confirmed the anomalous C(T) dependence, and found a second drop in specific heat below 1 K. In Lu₂Fe₃Si₅, we can reproduce C(T) below T_c, assuming two distinct energy gaps 2Δ ₁/k_BT_c = 4.4 and 2Δ ₂/k_BT_c = 1.1, with nearly equal weights, indicating that Lu₂Fe₃Si₅ is a two-gap superconductor similar to MgB₂. Hall coefficient measurements and band structure calculation also support the multiband contributions to the normal-state properties. The specific heat in the Sc₂Fe₃Si₅ single crystals also shows the two-gap feature. R₅Ir₄Si₁₀ (R = Sc, rare earth) is also a superconductor where competition between superconductivity and the charge-density wave is known for rare earths but not for Sc. We have performed detailed specific heat measurements on Sc₅Ir₄Si₁₀ single crystals and found that C(T) deviates slightly from the behavior expected for weak-coupling superconductors. C(T) for these superconductors can also be reproduced well by assuming two superconducting gaps.     

Luminescence properties of Sn2P2Se6 crystals

A large family of Sn_2yPb_2(1−y)P₂S_6xSe_6(1−x) semiconductor-ferroelectric crystals were obtained by the Bridgman technique. The photoluminescence properties of the Sn_2yPb_2(1−y)P₂S_6xSe_6(1−x) family crystals strongly depend on their chemical composition, excitation energy and temperature. The influence of the Pb → Sn and S → Se isovalent substitutions on the luminescence properties of a crystal with the Sn₂P₂Se₆ basic composition was investigated. A broad emission band observed in the Sn₂P₂Se₆ crystal with a maximum roughly at 600 nm (at T = 8.6 K) was assigned to a band-to-band electron-hole recombination, whereas broad emission bands, peaked near 785 nm (at T = 8.6 K) and 1025 nm (at T = 44 K) were assigned to an electron-hole recombination from defect levels localised within the bandgap. Possible types of recombination defect centres and specific mechanisms of luminescence in the Sn₂P₂Se₆ semiconductor-ferroelectric crystals were considered and discussed on the basis of the obtained results and the referenced data.     

Synthesis of a novel langanite-type compound La3Al5.5Nb0.5O14 by the sol-gel process

Langanite (La₃Ga_5.5Nb_0.5O₁₄, LGN) and its isomorphs are a few piezoelectric materials which have the unique temperature compensation and piezoelectric properties. But the high Ga₂O₃ content makes them very expensive and limits their applications. We reported a new langanite-type compound La₃Al_5.5Nb_0.5O₁₄ (LAN) which has the advantage of no Ga₂O₃ content. Chemically homogeneous La₃Al_5.5Nb_0.5O₁₄ sol was synthesized using La (NO₃)₃·6H₂O, Al (NO₃)₃·9H₂O and niobium citrate as starting materials. Single-phased LAN powder was prepared by decomposition of a citrate polymer precursor and subsequent reactions at high temperatures. TG-DTA, XRD and FTIR were employed to investigate the transformation process of gel to LAN powder. The results showed that, after calcination at 900 °C, pure La₃Al_5.5Nb_0.5O₁₄ polycrystalline powder with a narrow particle size distribution was obtained, which has the same structure with La₃Ga_5.5Nb_0.5O₁₄.