Electrical and dielectric properties of Ni0.5Co0.5GaxFe1.8-xO4(x≤1.0)spinel ferrite microspheres

Microspheres of Ni_0.5 Co_0.5Ga_xFe_2-xO₄(x≤1.0) microsphere spinel ferrites(NiCoGaFe-MSFs) and carbon spheres were prepared via a hydrothermal technique.The micro structure of microspheres was investigated through scanning and transmission electron microscopy(SEM and TEM),respectively,and X-ray diffraction(XRD).The electrical and dielectric properties of NiCoGaFe-MSF at temperatures ranging from20 to 120℃(between 293,1× 10³ and 393.1...     

Mechanical properties,thermal conductivity and defect formation energies of samarium immobilization in Gd2Zr2O7:First-principles study and irradiation experiment

A density functional theory(DFT) study was employed to investigate the mechanical property,thermal conductivity,Debye temperature,electronic structure and defect chemistry of(Gd_1-xSm_x)₂Zr₂O₇.All the(Gd_1-xSm_x)₂Zr₂O₇ compounds exhibit an excellent structural and mechanical stability(Gd_0.25Sm_0.75)₂Zr₂O₇ has the lowest Young’s modulus of...     

(Ni45Mn40Sn10Co5)100-xGdx合金的微观结构、马氏体相变及力学性能

研究了稀土Gd合金化对(Ni₄₅Mn₄₀Sn₁₀Co₅)_100-xGd_x(x=0,0.1,0.2,0.5,2,原子数分数,下同)磁性形状记忆合金的显微结构、马氏体相变及力学性能的影响.结果表明：低Gd掺杂量(x=0.1,0.2)对合金的相组成和显微组织影响甚微;当x(Gd)≥0.5时,合金中有第二相析出;在各成分合金中均观察到一步热弹性马氏体相变,随着Gd掺杂量的增加,单相合金(x=0～0.2)的马氏体相变温度单调上升,双相合金(x=0.5,2)的马氏体相变温度先下降后上升;适当的Gd掺杂量(x=2)能显著提高合金的压缩强度和延展性.     

微波辅助液相沉淀法合成Ca(MoO4)1-x(WO4)x:Eu3+红色荧光粉

以尿素为沉淀剂，采用微波辅助液相沉淀法合成了类球状双基质Ca(MoO₄)_1-x(WO₄)_x:Eu3+红色荧光粉，通过采用XRD、SEM、荧光光谱(PL)等现代分析技术对荧光粉的结构、形貌及发光性能进行了表征.结果表明，制备的Ca(MoO₄)_1-x(WO₄)_x:Eu3+红色荧光粉晶型完整，纯度高，为白钨矿结构；掺杂WO₄2-离子后，CaMoO₄:Eu3+红色荧光粉的发光性能明显增强，当WO₄2-离子的掺杂量x=0.4时，在395 nm激发下，在616 nm处的主发射峰的发光强度达到最大，掺杂浓度过高时会出现浓度淬灭现象.其较优的煅烧温度为1 000 ℃，煅烧时间为4 h.      

Effective regulation of electronic structures and luminescence properties of LiGd9(SiO4)6-x(GeO4)xO2:Dy3+ phosphors by tetrahedral substitution

A series of Dy³⁺-activated phosphors with the general formula LiGd₉(SiO₄)_6-x(GeO₄)_xO₂:Dy₃₊(0 ≤ x≤ 3)characterized by an apatite-type structure were successfully synthesized via a simple solid-state technique involving a partial substitution of [SiO₄]^4-with [GeO₄]^4- species.The effects of homovalent[GeO₄]^4--[SiO₄]^4- substit...     

Glycine-nitrate auto-combustion synthesis and magnetic properties of nanocrystalline NdAlxFe1-xO3 perovskites

The effect of substitution of Fe³⁺ by Al³⁺ on the structure and magnetic properties of NdAl_xFe_1-xO₃ perovskite nano-powders(x=0.0,0.1,0.2,0.3,0.4,and 0.5) prepared by the glycine-nitrate auto-combustion method was studied.All samples were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FT-IR),and energy dispersive X-ray spectroscopy(EDX).The magnetic properties of the samples ...     

Multiple magnetic transitions and magnetocaloric effect of Tb4Coln alloy

We report on the magnetic,magnetocaloric,thermal,and electrical transport properties of Tb₄Coln alloy,which crystallizes in two phases,Tb₆Co_2.1In_0.8(space group Immm) and Tb₂In_0.9Co_0.1(space group P6₃/mmc),respectively.The alloy reveals three successive magnetic transitions around T₁(163 K),T₂(50 K),and T₃(29 K),respectively,associated with paramagnetic to ferromagnetic transi...     

微合金化对双相中熵合金组织与力学性能影响研究

采用水冷铜坩埚磁悬浮熔炼和铜模负压吸铸法制备了(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_100-xCu_x,(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_100-xAg_x以及(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_100-2xCu_xAg_x (x=0,0.5,1,1.5和2;原子分数)3种中熵合金体系,探究了通过添加正的混合焓元素Cu,Ag合金化于面心立方(fcc)结构的中熵合金基体,调控组织制备了双相fcc的新型中熵合金,并采用Olson-Cohen热力学模型计算fcc中熵合金的层错能...     

Ce替代La对合金LaNi4.5Al0.5储氢性能及热力学的影响

金属Ce替代LaNi_4.5Al_0.5合金中的La用以提高金属吸/放氢热力学性能。通过研究合金La_1-xCe_xNi_4.5Al_0.5(x=0～0.4)的相结构、储氢热力学以及吸/放氢动力学发现,所制备的合金主相为六方晶系LaNi₅相;随着Ce替代量的增加(x=0～0.4),合金晶体结构中a轴呈现减小的趋势、c轴及各向异性(c/a)呈现出先增大后减小再增大的趋势;储氢性能测试表明,随着Ce替代量的增加,合金的吸/放氢平台压升高,最大储氢量减小;合金吸/放氢反应热优化程度与各向异性(c/a)呈现出相同趋势,当x=0.2时,合金吸放氢反应焓变分别降低至26.33 kJ/mol和24.30 kJ/mol。     

La1-x(La-Ce-Pr-Nd)xFe11Co0.5Si1.5合金的物相分析与磁热效应

采用电弧熔炼法制备了原子配比为La_1-x(La-Ce-Pr-Nd)_xFe₁₁Co_0.5Si_1.5(x=0、0.2、0.4、0.6、0.8、1.0)的合金,其中La-Ce-Pr-Nd为混合稀土。采用X射线衍射、扫描电镜和磁性测试方法研究了合金的物相组成和磁热效应。研究结果表明,当x≤0.4时,合金主要由NaZn₁₃型立方结构主相与少量的α-Fe杂相组成,当x>0.4时,除了NaZn₁₃型立方结构主相与α-Fe杂相,还出现了Th₂Zn₁₇型菱形结构的杂相,且其含量随x的增加而增多。随着混合稀土含量x的增加,NaZn₁₃型主相的晶格常数减小,居里温度降低。居里温度附近的Arrott曲线说明所有合金都发生了二级磁相变,但合金都具有较大的磁热效应,当外磁场变化为2 T时,x=0.6合金的等温熵变最大值为14.2 J·kg^-1·K^-1     

Magnetostriction and hysteresis of <110> oriented TbDyHoFe1.95 alloy

(Tb_0.36Dy_0.64)_1-xHo_xFe_1.95 magnetostrictive alloys with >110< orientation were prepared by zone melting directionally solidified method. The magnetostrictive performance and hysteresis of >110< aligned polycrystalline (Tb_0.36Dy_{0 64})_1-xHo_xFe_1.95 were investigated under applied magnetic field H (0>H>4 kOe) in the temperature range from ?60 to 80 °C with 0, 5 and 10 MPa pre-stress. The (Tb_0.36Dy_0.64)_1-x Ho_xFe_1.95 alloys (x>0.3) have the character of giant magnetostriction from ?60 to 80 °C. An obvious magnetostrictive “jump” effect was observed in these samples from ?60 to 80 °C. The pre-stress and temperature dependence of the W_h was also examined. Between the temperature range from ?60 to 80 °C, the magnetostriction increased with temperature decreased, while the magnetostriction hysteresis decreased, with the pre-stress increased, but the magnetostriction and the magnetostrictive hysteresis increased.     

Magnetostrictive properties and detection efficiency of TbDyFe/FeCo composite materials for nondestructive testing

In order to develop a highly sensitive material for nondestructive testing (NDT), (Tb_0.3Dy_0.7)Fe_1.95 thin films were deposited on FeCo substrates at room temperature by magnetron sputtering and annealed. The magnetostrictive properties and the detection efficiency of the composite films were investigated. Results demonstrate that the detection efficiency roughly shows regular consistency with the magnetostrictive strain of the TbDyFe films. Heat treatment has a great effect on the crystalline state and the magnetostrictive strain of the composite materials. The as-deposited (Tb_0.3Dy_0.7)Fe_1.95 films are amorphous, and the saturation magnetostriction (λ_s) is only 90 ppm. However, the nanostructured crystalline REFe₂ is partially separated out in amorphous matrix after annealing at 600 °C for 1 h, and the λ_s increases to 265 ppm. Simultaneously, the detection efficiency of the composite materials is obviously improved compared to that of the as-deposited films. The detection signal of traditional FeCo strip is 0.4 V at the excitation power of 1.0 P and frequency of 128 kHz and that of the strip increases significantly by depositing one layer of (Tb_0.3Dy_0.7)Fe_1.95 film. The detection signal of the composite material annealed at 600 °C is the best, even reaching saturation value of 2.5 V (1.0 P, 128 kHz). The results may provide us with a method for preparing new materials for NDT.     

Ce3+ sensitized Tb3+ and Dy3+ photoluminescence in β-LaB5O9 prepared by sol–gel method

Rare earth (RE) pentaborates, both α- and β-polymorphs, are good candidates for photoluminescent hosts suitable for various RE activators. Ce³⁺ acts not only as an activator itself, but also as a sensitizer to other rare earth activators, like in the case of commercial green phosphor CeMgAl₁₁O₁₉:Tb³⁺. In this work, two solid solutions of β-La_0.9–xCe_0.1Tb_xB₅O₉ (0 ≤ x ≤ 0.15) and β-La_0.9–yCe_0.1Dy_yB₅O₉ (0 ≤ y ≤ 0.07) were prepared by sol–gel method with high crystallinity, and the phase purity was confirmed with careful analyses on powder X-ray diffraction patterns. Energy transfers are expected due to the overlapping of Ce³⁺ emission with the Tb³⁺/Dy³⁺ excitation. Indeed, the steady photoluminescence spectra indicate the decrease of the Ce³⁺ emission and the increase of the Tb³⁺/Dy³⁺ emission, and the fluorescence decay curves exhibit the decrease of the average lifetime of Ce³⁺. The energy transfer efficiency is estimated to be 60% at x = 0.15 and 55% at y = 0.07, respectively. The mechanism is likely through the dipole–dipole electric interactions for both cases. With this rationale, the Tb³⁺ and Dy³⁺ emissions are greatly enhanced, in particular, the white emission of Dy³⁺ in β-La_0.85Ce_0.1Dy_0.05B₅O₉ is enhanced by 20 times.     

Influence of dysprosium concentration on sensitivity of luminescent thermometers of phosphors Ca_9Tb(PO_4)_5(SiO_4)F_2

Tb~(3+),Dy~(3+)-co-doped Ca_9 Tb_xDy_(1-x)(PO_4)_5(SiO_4)F_2 phosphors were prepared via high-temperature solidphase reaction method and the potential application in optical temperature measurements due to their color-tunable property was investigated in detail.The photoluminescence emission(PL) and photoluminescence excitation(PLE) spectra results show that the as-prepared phosphors exhibit both Tb~(3+) and Dy~(3+) emissions at 546 nm(~5 D_4-~7 F_5 transition of Tb~(3+)) and 587 nm(~4 F_(9/2)-~6 H_(13/2) transition of Dy~(3+)) upon376 nm excitation,respectively.In addition,the fluorescence decay analysis shows that the lifetime of the Tb3+emission rapidly decreases,which confirms the energy transfer existence between Dy~(3+) and Tb~(3+).Under 376 nm excitation,the temperature dependence of the fluorescence intensity ratios for the dualmission bands peaked at 546 and 587 nm was studied in the temperature range from 303 to 573 K.The results show that with the increase of Dy~(3+) concentration,the relative sensitivity first increases and then decreases,what's more,the maximum relative sensitivity is 3.142×10~(-3)%/K for Ca_9 Tb_xDy_(1-x)(PO_4)_5(SiO_4)-F_2(x=0.4).As a consequence,this preliminary study provides a novel method for exploring the novel thermo meters.     

Relationship between crystal growth mode,preferred orientation and magnetostriction of （Tb0.3Dy0.7）Fe1.95 alloys

The relationship between crystal growth mode, preferred orientation and magnetostrictive properties of （Tb0.3Dy0.7）Fe1.95 alloys was investigated at different directional solidification rates. The results showed that preferred orientation had a strong influence on the characteristics of （Tb0.3Dy0.7）Fe1.95 alloys. At lower solidification rates, the sample with 〈110〉 preferred orientation showed larger low-field magnetostriction and apparent compressive stress effect. The excessive solidification rate resulted in failure of preferred orientation and a poor magnetostrictive performance. With an increase in solidification rates, the crystal growth modes changed gradually from cellular and primary dendrite morphology to developed dendritic morphology. In addition, domain configurations were observed using magnetic force microscopy, and the change of magnetostrictive properties was interpreted in terms of revealing the domain configurations.     

Magnetic properties of Pr-Dy-Fe-Co-B sintered materials with a high cobalt content

Materials (Pr_1?x Dy _x )_12–17(Fe_1?y Co _y )_balB_5–15 (x = 0.44–0.51 at %, y = 0.15–0.87 at %) have been studied. It is shown that the abrupt decrease in the coercive force of the (Pr_1?x Dy _x )_12–17(Fe_1?y Co _y )_balB_5-15 sintered materials with x = 0.44–0.51 and y > 0.25 is determined by the amount of boron-containing phases. In this case, an increase in the boron content in the (Pr_0.72Dy_0.28)_14.5(Fe_0.50Co_0.50)_balB _z material with an unchanged dysprosium content leads to an increase in the coercive force by 4.5 times. It is assumed that the escape of boron from the near-surface areas of R ₂ F ₁₄B-phase grains leads to the formation of regions characterized by a low anisotropy constant, which serve as nuclei for the formation of reverse-magnetization domains.     

Energy transfer,superior thermal stability and multi-color emitting properties of langbeinite-type solid-solution phosphor K_2Dy_(1.5-x)Eu_xTa_(0.5)(PO_4)_3

Langbeinite type compounds are a large kind of oxometallate with good flexibility structure.Herein,we synthesized a new langbeinite type compound K_2 Dy_(1.5)Ta_(0.5)(PO_4)_3,in which the Dy~(3+) and Ta~(5+) were blended to occupy the same crystallographic sites.Simultaneously,solid solutions of K_2 Dy_(1.5)_(-x)Eu_xTa_(0.5)(PO_4)_3(x=0-1.5) were prepared and their photoluminescence properties were investigated.Due to energy transfer from Dy~(3+) to Eu~(3+),both Dy~(3+) and Eu~(3+) characteristic emissions are observed under 393 nm light excitation.The emitting color of K_2 Dy_(1.5-x)Eu_xTa_(0.5)(PO_4)_3 turns from green through yellow to red by simply adjusting the Eu~(3+) concentration from 0 to 0.4.Moreover,K_2 Dy_(1.48)Eu_(0.02)Ta_(0.5)(PO_4)_3 phosphor possesses excellent fluorescence thermal stability and exhibits zero thermal quenching at 150 ℃.These results manifest that K_2 Dy_(1.5-x)Eu_xTa_(0.5)(PO_4)_3 solutions are promising multi-color emitting phosphors candidate for near-UV LED.     

Directional solidification and heat treatment of terfenol-D magnetostrictive materials

Directional solidification techniques have been developed to produce grain-aligned rods of the highly magnetostrictive material Terfenol-D, Tb_xDy_1-xFe_y The magnetostrictive properties have been compared to those of single-crystal, bicrystal, and polycrystal rod prepared by a float zone melting (ZM) technique. It was found that the properties of the grain-aligned material were comparable to three-and four-grain ZM material and the magnetostriction for both materials was less than the ZM single crystal and the better bicrystal rods by around 20 pct. It was demonstrated that a heat treatment consisting of a 1-hour hold at 950 °C was very effective at improving the magnetostrictive properties of all of the materials. Experiments have demonstrated that, to be effective, the heat-treatment temperature must be above somewhere between 850 °C and 900 °C. It is postulated that the mechanism for the improved properties involves a relief or redistribution of residual stresses produced by localized melting near second-phase particles at the predicted eutectic temperature of around 875 °C in the Terfenol-D material.     

Wastewater treatment using Fe-doped perovskite manganites by photocatalytic degradation of methyl orange,crystal violet and indigo carmine dyes in tungsten bulb/sunlight

We documented(ⅰ) the decolorization of wastewater in visible light,which contains methyl orange,crystal violet and indigo carmine dyes,using La_0.7Sr_0.3Mn_1-xFe_xO₃(x=0.0,0.05,0.1 and 0.5) manganites and(ⅱ) efficient separation of photocatalysts from water using magnetic field.These ceramic photocatalysts were sintered at 1050℃ for 12 h.Ceramics were characterized by X-ray diffraction(XRD),soft X-ray absorption spectroscopy(SXAS),Fourier transf...