Nd3+:Y0.5Gd0.5VO4晶体生长和基本特性

Nd^3 :Y0.5Gd0.5VO4晶体作为一种新的激光材料，可以用中频感应加热提拉法生长。X射线粉末衍射分析表明它的结构与Nd^3 :YVO4晶体结构相同，它的晶格常数介于YVO4和NdVO4晶格常数之间。用ICP光谱法测定晶体中Nd^3 含量为0．8at％，分凝系数为0．8，与Nd^3 :GdVO4晶体中Nd^3 的分凝系数0．78相当；用称重法测定其密度为5．00g／cm^3；用稳态纵向热流法测出其室温热导率为12．5W／mK。实验表明Nd^3 :Y0.5Gd0.5VO4晶体有希望作为高功率ID泵浦激光晶体材料。     

纳米晶复合Nd9.5Fe81-xCoxZr3B6.5永磁材料磁性能的研究

采用熔体快淬及晶化退火工艺制备了Nd9.5Fe81-xCoxZr3B6.5(x=0、2、5、8、10)纳米晶合金条带,研究了Co的添加对快淬合金磁性能和居里温度的影响.结果表明,适量Co元素的添加能够有效降低各相晶粒的尺寸,增强了软、硬磁相晶粒的交换耦合作用,从而提高了合金的磁性能.Co含量为5%(原子分数)的合金,经670℃/4min的晶化处理后所得到的最佳磁性能为`Br=0.90T,jHc=588kA/m,(BH)max=117kJ/m3.     

(Fe0.5 Co0.5)73.5 Cu1 Mo3 Si13.5 B9合金高温磁性的研究

研究了460～580℃等温退火(30min)后纳米晶(Fe0.5 Co0.5)73.5 Cu1Mo3Si13.5B9合金高温软磁性能.结果表明,在Fe73.5Cu1Mo3Si13.5B9纳米晶合金中用Co取代部分Fe仍可形成双相纳米晶结构,并且可显著提高合金的高温特性.与Fe73.5Cu1Mo3Si13.5B9纳米晶软磁合金相比,其室温μi略有下降,但表征高温磁稳定性的居里温度明显提高,同时磁导率在高温下衰减变缓,从而拓宽了纳米晶软磁材料的高温使用范围.文中初步探讨了用Co取代部分Fe后使高温特性得到改善的机理.     

Spectroscopic properties and high-power laser operation of Yb0.14:Y0.77Gd0.09Ca4O(BO3)3 mixed crystal

We report, for the first time to our knowledge, on the spectroscopic properties and continuous-wave laser performance of Yb_0.14:Y_0.77Gd_0.09Ca₄O(BO₃)₃, a mixed rare earth calcium oxyborate Yb-ion crystal. Under simple end-pumping conditions with a 976-nm diode, efficient CW laser operation was demonstrated at room temperature, producing an output power of 14.1 W at 1084.4 nm with an optical-to-optical efficiency of 48%; while operating around 1045 nm, the laser could generate an output power as high as 23.0 W, with optical-to-optical and slope efficiencies amounting, respectively, to 57% and 70% with respect to incident pump power. The polarized absorption and emission cross sections are also presented. The impressive results demonstrated reveal the great potential of these mixed oxyborates in developing new promising Yb-ion laser crystals.     

Fe3O4缓冲层对CoFe2O4薄膜磁性能的影响

采用射频磁控溅射在基片Si（100）和Fe3O4（20nm）/Si（100）上制备了钴铁氧体（CoFe2O4）薄膜，制备的薄膜在空气气氛中进行300～1000℃的退火处理，采用XRD、VSM分析了薄膜的微结构以及磁性能。结果表明，制备的钴铁氧体薄膜均具有尖晶石结构，Fe3O4缓冲层薄膜促进了钴铁氧体薄膜的结晶，但降低了钴铁氧体薄膜的垂直各向异性和垂直于膜面方向的矫顽力，而钴铁氧体薄膜的磁化强度和矩形度得到了一定的提高。     

Spectroscopic properties of HoAl3(BO3)4 single crystal

The Judd–Ofelt theory has been applied to analyze absorption spectra of Ho³⁺ ion in HoAl₃(BO₃)₄ measured in spectral range 300–700 nm at room temperature. The Judd–Ofelt spectroscopic parameters have been determined as: Ω₂ = 18.87 × 10⁻²⁰ cm², Ω₄ = 17.04 × 10⁻²⁰ cm², Ω₆ = 9.21 × 10⁻²⁰ cm². These parameters have been used to calculate radiative lifetimes and branching ratios of the luminescence manifolds. Three luminescent bands were found in the spectral range 450–700 nm ascribed to transitions from the ⁵F₅, (⁵F₄, ⁵S₂) and ³K₈ states to the ground state ⁵I₈. Experimental intensities of these luminescence transitions were compared with those calculated by using Judd–Ofelt theory and the system of kinetic equations for populations of starting luminescing states. Probabilities of radiativeless transitions were evaluated from this comparison.     

Magnetic Properties of Superconducting and Nonsuperconducting (Nd0.33Eu0.33Gd0.33)Ba2Cu3Oy

The temperature dependence of the DC susceptibility (T) is measured between 1.7 and 350 K on superconducting and nonsuperconducting bulk melt-processed (Nd_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_y by means of SQUID magnetometry. A strong superconducting contribution is found to coexist with a large paramagnetic moment provided by the Nd and Gd ions. The paramagnetic contributions measured on both types of samples follow a Curie–Weiss law; however, an antiferromagnetic ordering is not observed down to 1.7 K.     

Spectroscopic properties of Er3+ ions in La2(WO4)3 crystal

Er³⁺-doped La₂(WO₄)₃ single crystals were grown by the Czochralski technique. The absorption spectra, fluorescence spectra and fluorescence decay curves of the crystals were measured at room temperature. The spectroscopic parameters, including intensity parameters Ω_t (t = 2, 4, 6), spontaneous emission probability, fluorescence branching ratio, radiative lifetime, and stimulated emission cross-section were estimated. The fluorescence decay curves of fluorescence manifolds ⁴I_13/2, ⁴I_11/2, and ⁴S_3/2 were measured for crystal and powder samples, respectively. The effect of radiation trapping on the spectroscopic parameters was discussed. Green up-conversion fluorescence bands centered at wavelengths of 530 nm and 550 nm were observed when the crystal was excited at 977 nm. The possible up-conversion mechanisms were proposed.     

Enhancing the microwave dielectric properties of Nd (Mg0.5Sn0.5)O3 ceramics by substituting Nd3+ with Ca2+

The microwave dielectric properties of Nd_(1?2x/3)Ca_x(Mg_0.5Sn_0.5)O₃ ceramics were examined to evaluate their exploitation for mobile communication. Nd_(1?2x/3)Ca_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd_2.9/3Ca_0.05(Mg_0.5Sn_0.5)O₃ ceramics revealed no significant variation of phase with the sintering temperature. Nd_2.9/3Ca_0.05(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1,550 °C for 4 h had the following properties: a density of 6.86 g/cm³, a dielectric constant (ε_r) of 19.3, a quality factor (Q × f) of 99,000 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?65 ppm/°C.     

Effect of the preparation route,PEG and annealing on the phase stability of Fe3O4 nanoparticles and their magnetic properties

Fe₃O₄ nanoparticles are synthesised via two different methods: (1) co-precipitation of Fe²⁺ and Fe³⁺ ions and (2) oxidative alkaline hydrolysis of Fe²⁺ ions under atmospheric pressure using different protective agents (PEG 200 and PEG 3000) and urea as a base. The preparation method and the polyethylene glycol (PEG) used are concurrently affecting the phase stability of the formation of the iron oxides: the co-precipitation method using PEG 200 (E4a) or PEG 3000 (E4b) leads to the formation of different ratios of Fe₂O₃ and Fe₃O₄, whereas the oxidative hydrolysis of Fe²⁺ using PEG 200 gives Fe₃O₄ (E2) powder as a major product. The average crystallites size of E4a and E4b is almost identical, i.e. around 19?nm but the saturation magnetisation of E4b is three times larger than that of E4a. The sample E2 shows the highest saturation magnetisation value 74?emu/g, with an average crystallites size of 71?nm. Transmission electron microscopy analysis confirmed that the E2 sample shows the presence of needles crystals with typical sizes around 10 and 50?nm and its selected area diffraction (SAD) shows a typical diffraction of the spinel structure of magnetite. On the other hand, E4b sample shows elongated nanoparticles with typical sizes around 24?nm and its SAD confirmed the presence of a mixture of Fe₂O₃ and Fe₃O₄ as many dispersed spots were obtained.     

Effect of Al3+-substitution on the electrical and magnetic properties of Ni1·05Sn0·05Fe1·9O4 ferrites

The effect of Al³⁺-substitution on d.c. resistivity, dielectric constant, initial permeability, saturation magnetization and Curie temperature has been studied for Ni_1·05Sn_0·05Al _x Fe_1·9−x O₄ ferrites, whereinx varies from 0 to 0·5 in steps of 0·1. The d.c. resistivity increases slowly forx⩽0·3 followed by a rapid increase forx>0·3. The variation is explained on the basis of Verwey hopping as well as polaron hopping mechanisms, and the dilution effect of Al³⁺ ions. The behaviour of dielectric constant is attributed to interfacial polarization and follows the Koops model. The saturation magnetization and the Curie temperature decrease continuously with increasing Al³⁺ content and are explained using the concepts of sublattice magnetization and exchange interactions. The decrease in initial permeability is attributed primarily to decrease in saturation magnetization. The dispersions in initial permeability and magnetic loss tangent are also discussed.     

Cr对纳米晶复合Nd2Fe14 B/α-Fe永磁材料磁性能的影响

采用快淬和晶化退火法制备了成分为Nd8.5Fe75-xCo5Cu1Nb1Zr3CrxB6.5(x=0.5,1,2)的纳米晶复合永磁合金.研究了Cr的添加对合金晶粒尺寸及磁性能的影响,结果表明适量Cr的添加能有效抑制磁性相晶粒长大,提高了合金的矫顽力.Cr含量为1%(at%),快淬速度为15.0m/s的合金经690℃/4min的晶化处理,由晶化磁粉粘结所得到的磁体最佳磁性能为:Br=0.62T,jHc=806.4kA/m,(BH)max=69.0kJ/m3.     

Nb的添加对Fe3B/Nd2Fe14B纳米永磁体磁性能与微观结构的影响

研究了微量合金元素Nb的添加对Fe3B／Nd2Fe14B型纳米复合永磁体微观结构与磁性能的影响规律。结果表明,添加Nb元素可以稳定非晶相,阻碍Fe3B粒子的结晶动力学。Nd5．5Fe70．0Co5Cu0．5Nb0．5B18．5非5晶合金在640℃退火处理30min可获得最佳磁性能：Br=1．05T,JHc=367kA／m,(BH)max=80．2kJ／m^3。Nb与Cu的复合添加对Fe3B晶粒的细化效果更显著;Nb元素的添加可以提高合金的磁性能,但添加量必须适中。     

Fe3O4纳米颗粒的溶剂热法制备及电磁特性研究

采用溶剂热方法分别在聚乙二醇、三乙二醇溶液中热分解乙酰丙酮铁,得到分散性能良好、尺寸均匀、形貌一致的Fe3O4纳米颗粒,颗粒尺寸为7～8nm。通过X射线衍射及透射电镜研究发现,两种溶液中制备样品均为面心立方结构,且在三乙二醇溶液中制备颗粒分散性更好。分别对两种样品进行磁测量,发现室温时均表现出超顺磁性,398kA/m时的磁化强度分别为50、40A·m2/kg。微波吸收测试显示,颗粒的分散性有利于改善样品的反射损耗。     

Structural properties of precipitates formed by hydrolysis of Fe3+ ions in Fe2(SO4)3 solutions

The structural properties of the solid phase, formed by the hydrolysis of Fe³⁺ ions in Fe₂(SO₄)₃ solutions at 90 or 120 °C, were investigated using X-ray diffraction,⁵⁷Fe Mössbauer spectroscopy, Fourier transform-infrared spectroscopy (FT—IR) and transmission electron microscopy. The concentration regions of Fe₂(SO₄)₃ were determined for the precipitation of goethite, -FeOOH, or hydronium jarosite, H₃OFe₃(OH)₆(SO₄)₂ as a single phase. Superparamagnetic behaviour of -FeOOH particles was observed. Hydrolysis of Fe³⁺ ions in 0.1 M Fe₂(SO₄)₃ solutions at 120 °C produced H₃OFe₃(OH)₆(SO₄)₂ and basic sulphate, Fe₄(OH)₁₀SO₄. The interpretation of⁵⁷Fe Mössbauer and FT—IR spectra is given.     

Nd3+A位置换对(Pb0.5Ca0.5)(Fe0.5Nb0.5)O3陶瓷微波介电性能的影响

研究了Nd³⁺离子A位置换改性(Pb_0.5Ca_0.5)(Fe_0.5Nb_0.5)O₃陶瓷的微波介电性能.[(Pb_0.5Ca_0.5)_1-xNd_x](Fe_0.5Nb_0.5)O₃(PCNFN)陶瓷的微波介电性能得到改善是由于少量过剩的Nd³⁺与(Pb,Ca)²⁺的固溶能够消除氧空位.当x=0.02时,能够形成单相的钙钛矿相,随着Nd³⁺置换量的增加,过剩的Nd³⁺将导致第二相焦绿石的形成,焦绿石会恶化PCNFN的微波介电性能.PCNFN介电性能随x的增加而下降是由于焦绿石相随x增加的结果.当x=0.02-0.05,PCNFN陶瓷有很好的微波介电性能,介电常数K>100,Qf值为5385-5797GHz,频率温度系数TCF随Nd³⁺含量的增加从正的变为负的.     

HDDR工艺条件及均匀化处理对Nd12.6Fe69.3Co11.6 B6.0 Al0.5合金磁性能的影响

研究了HDDR工艺条件(包括HD温度、HD时间、DR温度、DR时间)对Nd12.6Fe69．3Co11.6B6．0Al0．5合金磁性能的影响；比较了均匀化处理和未均匀化处理的合金经HDDR工艺后磁性能的差异；通过对两种舍金原始态的XRD谱线分析，找出存在差异的原因。     

Tuning of crystal phase and luminescence properties of Gd2(MoO4)3:Dy3+ phosphors

The orthorhombic and monoclinic Gd₂(MoO₄)₃:Dy³⁺ were successfully synthesized by a hydrothermal process with a subsequent annealing treatment at 800 °C for 4 h. The crystal phase of Gd₂(MoO₄)₃:Dy³⁺ was controlled as a function of the pH value of the solution. The crystallization and microstructures of the samples were characterized by Powder X-ray diffraction (XRD) and scanning electron micrograph (SEM). Furthermore, the optical properties were investigated by the diffuse reflection, excitation and emission spectra. The mechanisms of different crystal phases affected on the luminescence properties of Gd₂(MoO₄)₃:Dy³⁺ were discussed. The electric dipole–dipole interaction between Dy³⁺ ions was identified as the main mechanism for the concentration quenching of the two structures. Finally, the chromatic natures of all the samples were analyzed in detail. The results indicate that the orthorhombic phosphor Gd_1.84(MoO₄)₃:Dy_0.16³⁺ can be considered as a suitable candidate for white light emitting diodes (W-LEDs).     

Nd58Fe20Al10Co10B2大块非晶合金磁性能的研究

利用示羔扫描量热法，X射线衍射法、振动样品磁强计和扫描电镜研究了热处理对硬磁性非晶合金Nd58Fe20Al10Co10B2磁学性能的影响。研究表明，随着热处理温度的升高，非晶基体中的团簇的数量不断减少以及晶化过程中析出的晶体相或亚稳相对磁畴的钉扎作用的破坏，使矫顽力、剩余磁化强度、饱和磁化强度都逐渐降低。大量晶化后，Nd-Fe、Nd—Fe-(Al、Co)团簇之间耦合作用的消失是硬磁性消失的主要原因。