共查询到20条相似文献,搜索用时 343 毫秒
1.
采用MOCVD工艺在微米级Ni0.4Zn0.2Mn0.4Ce0.06Fe1.94O4(NZMCF)表面原位生长了纳米级羰基铁(CI)壳层,通过控制沉积温度,调控核壳形貌和吸波性能,得到了具有核壳结构的NZMCF -CI复合吸波剂,利用XRD、SEM、EDS及VNA等分析手段,重点研究了沉积温度对NZMCF -CI核壳粉体微观形貌、晶体结构、电磁参数及吸波性能的影响。结果表明:通过调节沉积温度,可以有效调控核壳粉体的形貌,进而调控吸波性能。沉积温度为220 ℃,NZMCF-CI核壳粉体具有最佳的形貌及吸波性能。利用测得的同轴环样品的电磁参数,计算出NZMCF -CI涂层在厚度为1.8 mm时,反射率最小值为-39.9 dB,小于-10 dB的吸波带宽为14.2 GHz(3.8~18 GHz)。涂层厚度为0.8~2.6mm时,在3.2~ 18 GHz均能实现最小反射率低于-20 dB,在2.5~18 GHz均能实现最小反射率低于-10 dB。仅需要调整厚度,即可以实现2~18 GHz内良好的吸波效果。 相似文献
2.
采用高温固相法合成了Cr3+掺杂的LiNi0.5Mn1.5O4正极材料,研究了掺杂量对材料物理性能和电化学性能的影响。利用XRD、SEM对材料的结构和形貌进行了表征,结果显示样品具有棱边清晰的尖晶石形貌。讨论了不同Cr3+掺杂量对LiCrxNi0.5-0.5xMn1.5-0.5xO4(x=0,0.05,0.1,0.15,0.2)正极材料性能的影响。充放电测试、循环伏安和交流阻抗测试结果表明:当Cr3+的掺杂量为x=0.1时(LiCr0.1Ni0.45Mn1.45O4)正极材料的性能最好,0.1C、0.5C、1C、2C及5C的首次放电比容量依次为131.54mAh g-1、126.84mAh g-1、121.28mAh g-1、116.49mAh g-1和96.82mAh g-1,1C倍率下循环50次,容量保持率仍为96.5%。 相似文献
3.
目的 研究离子掺杂对NiZn铁氧体电磁特性的影响,提高NiZn铁氧体的P波段吸波性能。方法 以NiO、ZnO、Fe2O3、CuO等为原料,采用高温固相反应法,通过球磨、预烧、造粒以及烧结等工艺,制备Cu2+掺杂的Ni0.22Zn0.66CuxMn0.04Co0.08–xFe2O4(x=0.04、0.05、0.06、0.07)铁氧体样品。通过XRD、VSM和SEM分别表征样品的晶格特征、磁学特性和微观形貌,利用阻抗分析仪对样品的电磁特性进行测量。结果 Cu2+掺杂量的增加引起NiZn铁氧体的A-B超交换作用减弱和磁晶各向异性降低,样品的Ms、Hc和Mr都呈现出减小的趋势。样品的复磁导率与其磁特性关系密切,随着Cu2+的增加,实部μ?减小,而虚部μ?增大。此外,Cu2+掺杂量的增加对Fe2+与Fe3+之间的电子迁移率产生影响,使得复介电常数实部ε?增大,而ε?增大的主要原因是Cu2+掺杂量的增加导致铁氧体内部产生了晶格缺陷。Cu2+的掺杂量对样品的P波段吸波性能影响显著,随着Cu2+掺杂量的增加,NiZn铁氧体的阻抗匹配特性明显改善,电磁衰减能力显著提高,这进一步降低了样品的最佳吸波匹配厚度。掺杂量x=0.07的NiZn铁氧体样品,在厚度为6.6 mm时,实现了有效吸波带宽完全覆盖P波段。结论 通过调节Cu2+的掺杂量可以调控NiZn铁氧体的P波段吸波性能,增加Cu2+掺杂量对于降低样品的P波段吸波匹配厚度有积极作用。 相似文献
4.
Cu1.8S作为一种P型半导体热电材料,具有环境友好、原料丰富、价格低廉等优点而受到广泛关注。本研究采用机械合金化(Mechanical Alloying, MA)结合放电等离子烧结(Spark Plasma Sintering, SPS)工艺制备了一系列Cu1.8S-x wt%BaTiO3 (x =0,0.075,0.1,0.15,0.2)块体材料,研究了复合纳米BaTiO3对Cu1.8S的相结构、微观形貌、热电性能及力学性能的影响。结果表明,纳米BaTiO3的加入不影响Cu1.8S的相结构、晶胞参数和载流子浓度;纳米BaTiO3均匀分布在Cu1.8S基体的晶界处产生钉扎效应进而细化晶粒并产生气孔。Cu1.8S-0.2 wt%BaTiO3样品在773 K时获得最低的热导率2.2 Wm-1K-1,所有样品的ZT值基本保持不变约0.39 (773 K)。同时Cu1.8S-x wt%BaTiO3块体样品的维氏硬度由82 (x = 0)增加到87 (x = 0.2)。本研究表明在Cu1.8S中复合纳米BaTiO3可以在不影响材料热电性能的前提下有效提升块体样品的力学性能,为后续Cu-S体系热电性能和力学性能的协同提升提供了思路,有利于制备高机械性能且稳定耐用的Cu-S体系的热电器件。 相似文献
5.
为了探索Ar/N2-Ar共溅射Ti掺杂对Ta2O5涂层光学性能和力学性能的影响,采用射频和直流磁控共溅射技术在玻璃基底表面制备了Ta2O5、N2-Ta2O5、Ti-Ta2O5和N2-Ti-Ta2O5涂层。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、原子力显微镜(AFM)表征了Ta2O5、N2-Ta2O5、Ti-Ta2O5和N2-Ti-Ta2O5涂层的微观结构和表面形貌;通过紫外可见分光光度计测试了涂层的光学参数;采用纳米压痕仪测试了涂层的硬度和杨氏模量。XRD测试结果表明,Ta2O5、N2-Ta2O5、Ti-Ta2O5和N2-Ti-Ta2O5涂层主要以Ta2O5为主体的非晶相结构组成。SEM和AFM结果显示,沉积在玻璃基底上的涂层未出现大面积空隙,溅射粒子在基底表面均匀堆积生长,并且涂层沉积厚度基本一致,厚度误差在5%以内。分别引入N2和Ti及N2-Ti共掺杂,均可降低Ta2O5涂层的粗糙度。光学测试结果表明,分别引入N2和Ti元素,可以提高Ta2O5涂层的平均透射率至81%以上,而N2-Ti共掺杂制备的N2-Ti-Ta2O5涂层平均透射率降低。力学测试结果显示,与Ta2O5涂层对比,N2-Ta2O5和N2-Ti-Ta2O5涂层的硬度显著增大,Ti-Ta2O5涂层硬度基本一致。弹性指数(H/E)和塑性指数(H3/E2)表明,N2-Ta2O5涂层和N2-Ti-Ta2O5涂层具备更好的断裂韧性和抗塑性变形能力。在玻璃表面制备Ta2O5掺杂N2和Ti元素的涂层,可以实现以N2-Ta2O5涂层和N2-Ti-Ta2O5涂层为代表的、同时具备优异光学性能和力学性能的多功能涂层。 相似文献
6.
采用真空电弧熔炼法制备了Zr1-xCoNbx (x = 0,0.05,0.1,0.15,0.2)合金,研究了Nb掺杂对合金晶体结构、吸放氢及抗歧化性能的影响。XRD结果表明:Zr1-xCoNbx (x = 0-0.2)合金主相为ZrCo相,含有少量ZrCo2杂相;其氢化物为ZrCoH3和ZrCo2相。Nb掺杂极大地提高了合金吸氢动力学性能,ZrCo吸氢反应活化时间为7690 s,Zr0.8CoNb0.2缩短至380 s。ZrCo吸氢反应活化能为44.88 kJ mol-1 H2,Zr0.8CoNb0.2降低至32.73 kJ mol-1 H2,有利于吸氢反应动力学性能。DSC测量结果表明:ZrCo放氢温度为597.15 K,Zr0.8CoNb0.2降低至541.36 K,放氢温度降低,有利于抗歧化性能。ZrCo合金放氢反应活化能为100.55 kJ mol-1 H2,Zr0.8CoNb0.2降低至84.58 kJ mol-1 H2。合金歧化程度随着Nb掺杂量增加而降低,798 K保温10 h,ZrCo歧化83.68%,Zr0.8CoNb0.2仅歧化8.71%,Nb掺杂降低8f2和8e位置氢原子数量,减小岐化反应驱动力。 相似文献
7.
在BiO--(Sr+Ca)O--CuO相图上的Bi2Sr2CaCu2O8+δ(Bi--2212) 相附近选择不同成分, 用分子束外延法制备成薄膜, 利用XRD, EDS,SEM和AFM研究了成分、衬底温度和臭氧分压对Bi--2212相薄膜成相的影响, 分析了生长速率和错配度对Bi--2212相薄膜质量的影响. 结果表明, Bi--2212相薄膜单相生成的成分范围 (原子分数) 分别为Bi 26.3%---32.4%, (Sr+Ca)37.4%---46.5%, Cu 24.8%---32.6%; 当衬底温度为720℃且臭氧分压为1.3×10-3 Pa时, 在MgO(100) 衬底上生长出质量较高的c轴外延Bi--2212相薄膜; 通过调整生长速率、更换衬底和插入不同厚度的Bi2Sr2CuO6+δ过渡层的方法, 可以改善Bi--2212相薄膜的结晶质量、表面形貌和导电特性. 相似文献
8.
采用镁扩散方法制备了Pr6O11纳米颗粒添加的MgB2超导块体,研究了Pr6O11掺杂对其临界电流密度(Jc),不可逆磁场(Hirr)和上临界磁场(Hc2)的影响。实验结果表明Pr6O11纳米颗粒掺杂明显提高了块体的Jc,Hirr和Hc2,但没有降低其超导转变温度Tc。在20 K自场条件下,质量比为1 wt.% Pr6O11掺杂的MgB2块体的Jc较没掺杂样品提高了将近5倍, Jc=3.61×105A/cm2。在10 K温度下,MgB2块体Hc2 和Hirr较没掺杂样品分别提高了1.9 T and 2.6 T。同时讨论了Pr6O11纳米颗粒掺杂对MgB2块体的电性能和磁通钉扎机制的影响。 相似文献
9.
通过模板辅助溶胶-凝胶法制备了一系列的Mn1-xZnxFe2O4(0≤x≤1,步长为0.2)纳米粉体。利用XRD和VSM对材料的物相和磁性能进行了表征,主要研究了Mn1-xZnxFe2O4分子式中Zn含量的变化对样品的微观结构和磁性能的影响。实验结果表明,具有不同Zn含量的Mn1-xZnxFe2O4样品均为尖晶石结构;随着Zn含量的增加,样品的晶面间距d、平均晶粒尺寸D、饱和磁化强度Ms和居里温度Tc都呈现出下降的趋势,而样品的矫顽力Hc则呈现出先升高后降低的趋势。分析认为,Ms的下降可以用Yafet-Kittel倾角理论解释,Tc的降低归因于晶格中反铁磁性耦合的降低,而Hc的变化则主要是由于材料的磁晶各向异性常数K1的变化引起的。 相似文献
10.
制备了不同 Mn 含量的IrO2-Ta2O5-MnOx电极。揭示了Mn含量对该类电极的物理和电化学特性的影响。结果表明,涂??覆的IrO2-Ta2O5-MnOx层由于其凹凸不平的多孔结构而具有较大的比表面积。少量Mn的加入抑制了活性成分IrO2的结晶,并将其转化为Ir3+。适当地用 Mn 代替Ir可以显著提高 IrO2-Ta2O5-MnOx 电极的电催化性能。高的电催化活性、长的寿命和低的成本得益于 Mn 掺杂的电极具有更大的活性表面积,从而促进了硫酸溶液中氧的析出。 相似文献
11.
Xihong Hao Jiwei Zhai Jing ZhouZhenxing Yue Jichun YangWenguang Zhao Shengli An 《Journal of Alloys and Compounds》2011,509(2):271-275
In this paper, we report on the structure and electrical properties of lead zirconate (PbZrO3) thin films doped with barium (Ba2+) and strontium (Sr2+) deposited on platinum-buffered silicon substrates by a sol-gel method. Effects of Ba2+ and Sr2+ dopants on microstructure and electrical properties of the PbZrO3 antiferroelectric thin films were investigated in details. X-ray diffraction patterns and scanning electron microscope micrographs illustrated that orientation and surface microstructure of these antiferroelectric films were dopant-dependent. The dielectric measurements showed that Sr2+ doping stabilized the antiferroelectric phase, while Ba2+ doping destabilized the antiferroelectric phase. It was also found that fatigue property of the antiferroelectric PbZrO3 thin films was improved remarkably by the dopants. 相似文献
12.
The effect of LMO doping on the structure, magnetic and magnetotransport properties of La0.8Sr0.2MnO3 (LSMO)/xLaMnO3 (LMO) has been investigated. Two types of LSMO/xLMO composites, named as SLx (low temperature sintered samples) and SHx (high temperature sintered samples) samples, were prepared by different sintering temperature and solid-state reaction method. The presence of LMO at the grain boundaries increases the disordered states at the surface of the grains and therefore the magnetization and transition temperature decrease by increasing the amount of LMO doping level. Results show that the rate of decreasing of transition temperature is much more for high temperaure sintered samples. Also the resistivity of samples increases by the increase of LMO doping level. Results also show that the LMO doping has an effect on a low field magnetoresistance (LFMR). The value of LFMR increases for low doping level of 0 ≤ x ≤ 15, for SLx samples and 0 ≤ x ≤ 10 for SHx samples. Also LFMR decreases at high doping level. The spin dependent tunneling and scattering at the interfaces of the grain boundaries are responsible for the increase of LFMR at low doping level, while reduction of LFMR at high doping level may result from the grain boundary becoming too thick for electron tunneling. 相似文献
13.
The structural, electrical transport and magnetic properties have been studied for compounds: La1−xSrxFe1−xMnxO3 (0.3 ≤ x ≤ 0.7). The lattice parameter, a, first decreases with x, and followed by an increase when Sr2+ and Mn4+ was continuously doped. The cell parameters, b and c, slightly decrease with coupled substitution of Sr2+ for La3+ and Mn4+ for Fe3+. In the paramagnetic temperature range, formation of magnetic clusters is suggested; the sizes of clusters decrease with x up to 0.5, following that they increase sharply with continuing doping. The electrical behaviors of all specimens demonstrate insulators and the electrical resistivity increases with content of Mn4+ and Sr2+ ions doped. A variable range hopping model is suitable to describe electrical transport process for the compounds at low temperature. At high temperature the electrical transport process can be described by bipolaron model for all compounds. 相似文献
14.
Zupei Yang Lijuan ZhangXiaolian Chao Lirong XiongJie Liu 《Journal of Alloys and Compounds》2011,509(35):8716-8719
The Ca1−xSrxCu3Ti4O12 (CSCTO) giant dielectric ceramics were prepared by conventional solid-state method. X-ray diffraction patterns revealed that a small amount of Sr2+ (x < 0.2) had no obvious effect on the phase structure of the CSCTO ceramics, while with increasing the Sr2+ content, a second phase of SrTiO3 appeared. Electrical properties of CSCTO ceramics greatly depended on the Sr2+ content. The Ca0.9Sr0.1Cu3Ti4O12 ceramics exhibited a higher permittivity (71,153) and lower dielectric loss (0.022) when measured at 1 kHz at room temperature. The ceramics also performed good temperature stability in the temperature range from −50 °C to 100 °C at 1 kHz. By impedance spectroscopy analysis, all compounds were found to be electrically heterogeneous, showing semiconducting grains and insulating grain boundaries. The grain resistance was 1.28 Ω and the grain boundary resistance was 1.31 × 105 Ω. All the results indicated that the Ca0.9Sr0.1Cu3Ti4O12 ceramics were very promising materials with higher permittivity for practical applications. 相似文献
15.
Ti3SiC2/cordierite coatings with different critical plasma spray parameters (CPSP) were fabricated via atmospheric plasma spraying method. The microstructure and phase constitution of the as-sprayed Ti3SiC2/cordierite coatings were characterized. The effects of CPSP conditions on the electromagnetic shielding, and dielectric and microwave absorption properties of coatings in the frequency of 8.2-12.4 GHz were also measured and investigated. The results showed that both real and imaginary part of the complex permittivity decrease with increasing CPSP values, which can be ascribed to the decomposition of some Ti3SiC2 into TiC. The calculated reflection loss of the as-sprayed Ti3SiC2/cordierite coatings with different CPSP conditions and thicknesses indicates that coatings with CPSP 0.3, 0.35, and 0.425 exhibit excellent microwave absorption property in the thickness of 1.5 mm. In order to broaden the bandwidth of the coatings, a double-layer coating system was designed. The calculated reflection loss results show that when the thickness of matching layer is 0.3 mm and the thickness of absorbing layer is 1.5 mm, the double-layer coating system shows a proper microwave absorption property with a minimum absorption value of ?17.37 dB at 9.67 GHz and a absorption bandwidth (RL less than ?5 dB) of 4.16 GHz in the investigated frequency. 相似文献
16.
Young-Min Kang Alexander N. Ulyanov Sung-Yun Lee Sang-Im Yoo 《Metals and Materials International》2011,17(6):1045-1053
We report the low field magnetoresistance (LFMR) properties of (La0.75Sr0.25)1.05Mn0.95O3(LSMO) films on a-SiO2/Si substrates, prepared by ex-situ solid phase crystallization of amorphous films deposited by dc-magnetron sputtering at room temperature. The average grain
size of the LSMO films was gradually increased with increasing annealing temperature (T
an
) and film thickness. High T
an
also caused the growth of an amorphous inter-diffusion layer between a-SiO2 and LSMO. The highest LFMR values of 16 and 1.0 % were achieved at 100 K, 1.2 kOe and 300 K, 0.5 kOe, respectively, from
an LSMO film of 200 nm thickness annealed at 900 °C. In accordance with a modified brick layer model, grain boundary areal
resistance gradually increased with increasing T
an
and decreasing film thickness due to the penetration of the amorphous inter-diffused phase into the LSMO grain boundary.
Improved LFMR values are attributable to modification of the LSMO grain boundary into a more effective spin-dependent scattering
center. 相似文献
17.
G. Murtaza Rai Faiza aenMisbah-ul-Islam M.U. Rana 《Journal of Alloys and Compounds》2011,509(14):4793-4796
We have prepared BaCd2−xSrxFe16O27 (x = 0, 0.5, 1, 1.5 and 2.0) W-type hexagonal ferrites by standard ceramic method. In this work, the structural, dielectric and magnetic properties have been studied of the prepared samples. The XRD analysis of the samples reveals single phase behavior sintered at 1400 °C for 6 h. The saturation magnetization (Ms) shows increasing behavior with the increasing concentration of Sr2+. While the coercivity (Hc) decreases rapidly up to 409 G for x = 1.5 and then increases for (x > 1.5) due to the preference of Cd2+ for tetrahedral sites and the number of spin-down magnetic ions. The real and imaginary parts of the dielectric constant (?′,?″) and dielectric loss tangent (tan δ) are determined in the frequency range 0.1-107 Hz. It is observed that both the real and imaginary parts of the dielectric constant and tan δ decrease with the increasing concentration of Sr2+, which is due to the contribution of Cd2+ ions in addition to Fe3+ and Fe2+ ions to interfacial polarization. 相似文献
18.
Fuhe Le Luxiang Wang Wei Jia Dianzeng Jia Shujuan Bao 《Journal of Alloys and Compounds》2012,512(1):323-327
A novel phosphor Sr2P2O7 co-doped with europium ion and chlorine ion was firstly synthesized by solid state reaction under air atmosphere. Its properties were systematically analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fluorescence spectra. The introduction of chlorine into the system was helpful and necessary to Eu3+ substitute Sr2+ site and subsequently to reduce Eu3+ to Eu2+, XPS results confirmed that some amount of Eu3+ ions could be reduced to Eu2+ ions under air atmosphere at high temperature. The reduction tendency of Eu3+ depends not only on the doping Cl− content, but also on the sintering temperature and time. Photoluminescence spectra also revealed that europium ions were present in divalent as well as trivalent oxidation states, the emission peak at 415 nm is ascribed to the typical 5d-4f transition of Eu2+, 592 nm and 613 nm assigned to the characteristic transitions of 5D0-7F1,2 of Eu3+. Such abnormal reduction was attributed to the electronegative defects formed by nonequivalent substitution of Eu3+ on the Sr2+ sites in the investigated phosphors. 相似文献
19.
La0.8Ba0.2MnO3 nano-particles were synthesized by sol-gel process, and the crystal structure and morphology' were characterized by XRD and SEM, respectively. The complex permittivity and permeability were determined by microwave vector network analyzer in the frequency range of 2-18 GHz. The relationship between reflection coefficient and microwave frequency of La0.8Ba0.2 MnO3 was calculated based on measured data. The results show that the average diameter of La0.8Ba0.2MnO3 crystal powders is about 80 nm and the crystal structure is perovskite when being calcined at 800 ℃ for 2 h. The microwave absorbing peak is 13 dB at 6.7 GHz and the effective absorbing bandwidth above 10 dB reaches 1.8 GHz for the sample with the thickness of 2.6 mm. The microwave absorption can be attributed to both the dielectric loss and the magnetic loss from the loss tangents of the sample, but the former is greater than the latter. 相似文献
20.
Fenghe Wang Dongzhan ZhouShuyuan Ma Hongwei YuPanlai Li Zhiping Yang 《Journal of Alloys and Compounds》2011,509(14):4824-4827
Eu2+-doped Sr3La(PO4)3 phosphors were synthesized by solid-state reaction method. Their luminescent properties were investigated. The phosphor could be excited by ultraviolet light effectively. The emission spectra exhibit two emission peaks located at 418 nm and 500 nm, respectively. These two peaks originated from two different luminescent centers, respectively. One is nine-coordinated Eu(I) center, other is six-coordinated Eu(II) center. It was found that the doping concentration of Eu2+ ions affected the shape of emission spectra. As the doping concentration increasing, Eu2+ ions are more likely to form Eu(I) luminescent centers and emit purple light. 相似文献