Effect of Nd3+ substitution on structural and magnetic properties of Mg–Cd ferrites synthesized by microwave sintering technique

Nd~(3+) substituted spinel ferrites with formula Mg_xCd_(1-x)Nd_(0.03)Fe_(1.97)O_4(x = 0.0.2,0.4,0.6.0.8 and 1.0)were prepared by oxalate co-precipitation method using novel microwave sintering technique. AR grade sulphates were used as starting chemicals. The samples were sintered at optimized power of 70 W for10 min in a microwave oven(800 W). The structural analysis of these samples was done by using X-ray diffraction, scanning electron microscope and Fourier transform IR techniques. The XRD analysis of the synthesized ferrite confirms the formation of cubic spinel structure of ferrite. The influence of Nd3+substitution on various structural parameters of Mg-Cd ferrites was reported. IR study indicates the spectra contain two intense absorption bands around 600 and 400 cm~(-1) in addition with four extra bands. The magnetic properties of all ferrites were studied by using a vibration sample magnetometer.The crystallite and grain size dependant magnetic properties are observed. The composition Mg_(0.6)Cd_(0.4)Nd_(0.03)Fe_(1.97)O_4 has better magnetic properties that can be used in recording media. The fast synthesis of spinel ferrites is yielded due to use of the microwave sintering technique.     

Systematic study of Ce3+ on the structural and magnetic properties of Cu nanosized ferrites for potential applications

Ce~(3+) substituted Cu-spinel nanoferrites CuCe_xFe_(2-x)O_4(x=0.00, 0.02, 0.04, 0.06, 0.08 and 0.10) were synthesized via sol-gel self-combustion hybrid route. Single phase spinel ferrite of Cu nanoferrites were examined using X-ray diffraction(XRD) analysis whereas the multiphase structure was observed as Ce contents increased from x=0.06. Field emission scanning electron microscopy(FESEM), Thermogravimetric and differential thermal analysis(TGA and DTA) and Fourier transform infrared spectroscopy(FTIR) were used to find out the morphology phase and metal stretching vibrations of Ce~(3+) substituted nanocrystalline ferrites. The crystallite size was increased and found in the range of 25-91 nm. The agglomerations in Cu ferrite samples increase as the Ce~(3+) concentration increases. The magnetic properties such as remanence, saturation magnetization, coercivity, Bohr magneton and magnetocrystalline anisotropy constant(K) were determined using M-H loops recorded from a vibrating sample magnetometer(VSM). Saturation magnetization, remanence and coercivity are increased as the Ce~(3+)contents increase in Cu nanocrystalline samples. Moreover, law of approach to saturation(LoA) was used to calculate the maximum value of saturation for Ce-doped Cu nanoferrites. The soft magnetic behaviour of the Cu nanoferrite is observed as compared to the samples substituted with the increased Ce contents in Cu nanocrystalline ferrite. Bohr magneton and magnetocrystalline anisotropy are found to increase with the substitution of rare earth Ce~(3+) contents in Cu spinel nanocrystalline ferrite. Cedoped Cu nanocrystalline ferrites with excellent properties may be suitable for potential applications in sensing, security, switching, core, multilayer chip inductor, biomedical and microwave absorption applications.     

Ultraviolet to near-infrared energy transfer in NaYF_4:Nd~(3+),Yb~(3+) crystals

To convert ultraviolet(UV) light into near-infrared(NIR) light in phosphors is demanded for the development of solar cells.A series of NaYF_4:Nd~(3+),Yb~(3+) white powder samples were prepared via the hydrothermal method.The crystal structure and photoluminescence properties of the samples were carefully studied using X-ray diffractometry(XRD) and photoluminescence spectra.The excitation and emission spectra of NaYF_4:Nd~(3+),Yb~(3+) samples and the luminescence decay curves of Nd~(3+) and Yb~(3+) revealed an efficient energy transfer process from Nd~(3+) to Yb~(3+).This process resulted in the Yb~(3+) NIR fluorescent emission at 980 nm.Moreover,the lifetime of the Nd~(3+4)F_(3/2) level decreased with the increase of Yb~(3+) doping concentration.The build-up time of the decay curves of the Yb~(3+2)F_(5/2) level further verified the energy transfer process.Meanwhile,energy transfer efficiency based on different Yb~(3+) doping concentrations was achieved.     

Characterization of X80 and X100 Microalloyed Pipeline Steel Using Quantitative X-ray Diffraction

Quantitative X-ray diffraction characterization of four (4) X80 and three (3) X100 microalloyed steels was undertaken. The effect of through-thickness position, processing parameters, and composition on the measured crystallite size, microstrain, and J index (relative magnitude of crystallographic texture) was determined. Microstructure analysis using optical microscopy, scanning electron microscopy, transmission electron microscopy, and electron-backscattered diffraction was also undertaken. The measured value of microstrain increased with increasing alloy content and decreasing cooling interrupt temperature. Microstructural features corresponding to crystallite size in the X80 steels were both above and below the detection limit for quantitative X-ray diffraction. The X100 steels consistently exhibited microstructure features below the crystallite size detection limit. The yield stress of each steel increased with increasing microstrain. The increase in microstrain from X80 to X100 is also associated with a change in microstructure from predominantly polygonal ferrite to bainitic ferrite.     

Structural characterization and optical properties of long-lasting CaAl_2O_4:Eu~(2+),Nd~(3+) phosphors synthesized by microwave-assisted chemical co-precipitation

The present paper reported the structural and luminescent properties of Eu~(2+) and Nd~(3+) doped CaAl_2O_4 phosphor. The samples were prepared by microwave-assisted chemical co-precipitation(MA-CCP), a synthesis technique which is suitable for small and uniform particle that could be used directly without grinding. The effects of different microwave temperatures on structure and photoluminescence behavior were studied. Formation of a phosphor and phase purity were confirmed by X-ray diffraction technique(XRD) with variable microwave temperatures. XRD analysis showed that the phosphors prepared by MA-CCP method at the temperature of 750, 900oC, respectively and solid-state reaction(SSR) method at 1300oC consisted of impurities. Commission Internationale de L'Eclairage(CIE) color coordinates of CaAl_2O_4:Eu~(2+),Nd~(3+) were suitable as blue light emitting phosphor. Excitation and emission peaks of the samples prepared by different methods in this study were almost the same. The images of SEM showed that the size of the phosphors prepared by MA-CCP method reached a submicrometer.     

H2BPMPBD和TOPO协同萃取Ln3+的研究

研究了1,4-双(1'-苯基-3'-甲基-5'-氧代吡唑-4'-基)丁二酮(H2BPMPBD,简为H2A)和三正辛基氧化膦(TOPO)的氯仿溶液从硝酸介质中对Ln3+的协同萃取.用斜率法确定了萃合物的组成为LaA·HA·TOPO,考察了萃取剂浓度和溶液酸度对萃取机理的影响,测定了半萃取pH1/2值和萃取反应平衡常数Ks.e,求得了反应的焓变和熵变.     

Spectroscopic properties and energy transfer of Nd3+/Ho3+-doped Ga2O3-GeO2 glass by codoping Yb3+ ion

This study presented the luminescence properties of Nd³⁺/Yb³⁺/Ho³⁺ dopant ions inside a host based on Ga₂O₃-GeO₂-Li₂O（GGL） glass. The measured differential scanning calorimetry result showed that GGL glass exhibited excellent stability against devitrification with ?T=135 oC. Obvious 543 and 657 nm emissions were observed in Nd³⁺/Ho³⁺-codoped sample. The incorporation of Yb³⁺ into Nd³⁺/Ho³⁺-codoped glass system had resulted in enhanced upconversion emission intensity under the excitation of 808 nm and/or 980 nm laser diode（LD）. The possible mechanisms and related discussions on this phenomenon were presented. It was noted that the presence of Yb³⁺ yielded an enhancement about 7 and 11 times in the 543 and 657 nm emission intensities respectively under 808 nm excitation due to the energy transfer from Nd³⁺ to Ho³⁺ via Yb³⁺ ion. Here Yb³⁺ played a major role as a bridging ion. While enhanced 543 and 657 nm emission intensities under the excitation of 980 nm LD originated from the sensitization effect of Yb³⁺. Our results showed that Nd³⁺/Ho³⁺/Yb³⁺ triply doped GGL glass might be a promising candidate for the development of visible-laser materials.     

Structure formation in grade 20 steel during equal-channel angular pressing and subsequent heating

The structure formation and the mechanical properties of quenched and tempered grade 20 steel after equal-channel angular pressing (ECAP) at various true strains and 400°C are studied. Electron microscopy analysis after ECAP shows a partially submicrocrystalline and partially subgrain structure with a structural element size of 340–375 nm. The structural element size depends on the region in which the elements are formed (polyhedral ferrite, needle-shaped ferrite, tempered martensite, and pearlite). Heating of the steel after ECAP at 400 and 450°C increases the fraction of high-angle boundaries and the structural ferrite element size to 360–450 nm. The fragmentation and spheroidization of cementite lamellae of pearlite and subgrain coalescence in the regions of needle-shaped ferrite and tempered martensite take place at a high ECAP true strain and heating temperature. Structural refinement ensures considerable strengthening, namely, UTS 742–871 MPa at EL 11–15.3%. The strength slightly increases, whereas the plasticity slightly decreases when the true strain increases during ECAP. After ECAP and heating, the strength and plastic properties of the grade 20 steel remain almost the same.     

Near-infrared luminescent Nd~(3+)/Yb~(3+)-codoped metal-organic framework for ratiometric temperature sensing in physiological range

Self-calibrating luminescent thermometry employing luminescence within the optical transparency windows provides a promising prospect for temperature measurement in the biological fields.In this work,a new Nd~(3+)/Yb~(3+)-codoped metal-organic framework Nd_(0.95)Yb_(0.05)BPTC showing threedimensional anionic network,obtained by reacting ligand [1,1'-biphenyl]-3,3',5,5'-tetracarboxylic acid(H_4BPTC) with Nd~(3+) and Yb~(3+) ions under solvothermal conditions,is reported.Upon 808 nm photoexcitation,Nd_(0.95)Yb_(0.05)BPTC simultaneously emits the characteristic near-infrared luminescence of Nd~(3+) and Yb~(3+) ions based on the efficient energy transfer from Nd~(3+) to Yb~(3+) ions.In addition,the emission intensity ratio of Yb~(3+) and Nd~(3+) shows good exponential-like response to temperature in the physiological range of 293-323 K.The feature properties of Nd_(0.95)Yb_(0.05)BPTC include near-infrared absorption and emission,favorable temperature sensitivity and accurate temperature uncertainty,as well as good chemical stability,making such system useful in biomedical applications.     

Recent progress of energy transfer and luminescence intensity boosting mechanism in Nd~(3+)-sensitized upconversion nanoparticles

Rare earth doped upconversion nanoparticles can be considered as the spice of research in the field of luminescence nanomaterials due to their unique optical properties such as near-infrared excitation.Enormous works have been reported about biomedical applications of 980 nm excited and Yb~(3+)-sensitized upconversion nanoparticles.However,980 nm excitation wavelength overlaps with the absorption band of water molecules in the biological environment,leading to overheating effect that can induce thermal damages of normal cells and tissues.Recently,Nd~(3+)-sensitized upconversion nanoparticles which can be excited with 808 nm has been widely investigated as alternative nanoparticles that can surmount this issue of overheating effect.Even though Nd~(3+)-sensitized upconversion nanoparticles can reduce the overheating effect by 20 fold as compared to Yb~(3+)-sensitized counterpart,there are several factors that reduce the upconversion luminescence intensity.In this review article,photon energy harvesting and transferring mechanisms in Nd~(3+),Yb~(3+)and emitter ions co-doped upconversion nanoparticles under 808 nm excitation are briefly discussed.Factors that affect upconversion luminescence intensity and quantum yield of Nd~(3+)-sensitized upconversion nanoparticles are also addressed.Besides,some of the important strategies that have been recently utilized to boost upconversion luminescence intensity of Nd~(3+)sensitized upco nversion nanoparticles are tho roughly summarized.Lastly,the future challenges in the area and our perspectives are in sight.     

Microwave electromagnetic and absorbing properties of Dy3+doped MnZn ferrites

Dy3+ doped Mn-Zn ferrites Mn0.3Zn0.7Fe2-xDyxO4(x=0,0.01,0.02,0.03,0.04)were prepared by the conventional solid-state reaction.The crystal structure,surface morphology and electromagnetic properties of the calcined samples were characterized by X-ray diffraction analysis(XRD),scanning electron microscopy(SEM) and network analyzer(Agilent 8722ET).All the XRD patterns showed the single phase of the spinel-type ferrite without other intermediate when x≤0.03.The average crystallite size was about 44?56 nm.The mi...     

Effect of transformation substructure on the strength and toughness of Fe−Mn alloys

Phase transformations in Fe?Mn alloys containing up to 9 pct Mn were studied by optical and electron transmission microscopy. Either equiaxed ferrite, massive ferrite, or massive martensite can form on cooling from austenite. The particular type of transformation product formed was found to depend on the alloy content, austenite grain size, and cooling rate. The mechanical properties of all the transformation products were evaluated using tensile and impact testing and are discussed in terms of the observed microstructural features. Yield strength and impact transition temperature were found to be relatively insensitive to manganese content but were strongly influenced by the transformation substructure and grain size of the transformed phase. In martensite it has been shown that the structural unit analogous to grain size in ferrite is the martensite packet size, which in turn is controlled by the prior austenite grain size. The fracture surface of broken impact specimens and the fracture profile were examined by means of electron and optical microscopy techniques. These fractographic observations were correlated with impact test data and microstructural observations of the various transformation products.     

Influence of La-Co substitution on the structure and magnetic properties of low-temperature sintered M-type barium ferrites

La-Co substituted M-type barium ferrites (BaM) were prepared by traditional solid state method and sintered at low tem-perature (1173 K). X-ray diffraction (XRD), scanning electron microscopy (SEM) and...     

Structure and magnetic properties of nanocrystalline Ni0·64Zn0·36Fe2O4 powders prepared by ball milling

Abstract

In this study, nanocrystalline Ni_0·64Zn_0·36Fe₂O₄ powders were prepared using a planetary ball mill. The evolution of the microstructure and magnetic properties during the milling were studied by X-ray diffraction technique, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometre. It is revealed from the results of the phase analysis that nanocrystalline Ni_0·64Zn_0·36Fe₂O₄ ferrite with average crystallite size of 6·18 nm and non-uniform lattice strain of 0·33% has been formed after 60 h of milling time. A progressive increase of saturation magnetisation and a dramatic decrease in coercivity were also observed with increasing milling time.     

Effect of RE~(3+) electronegativities on luminescence property of Ba_5Si_8O_(21):Eu~(2+) persistent phosphor

A series of Ba_5Si_8O_(21):0.02Eu~(2+),0.09RE~(3+) persistent phosphors were synthesized by the solid-state reaction method.The measurement results of photoluminescence(PL),phosphorescence and thermoluminescence(TL)were analysed and discussed.The XRD results showed that samples codoped with different RE~(3+) were Ba_5Si_8O_(21) single pure phase.Under the excitation,all samples exhibited a broad Eu~(2+) characteristic emission,and the La~(3+) co-doped sample emitted the brightest photoluminescence even though its persistent luminescence property was the worst because of the weakest electronegativity.However,Nd~(3+) electronegativity was suitable,thus after activation,the Ba_5Si_8O_(21):Eu~(2+),Nd~(3+) sample had the best persistent luminescence performance with the highest phosphorescence intensity and the persistent luminescence decay time beyond 8 h.The Nd~(3+) co-doped sample also had the largest thermoluminescence integral area which proved effectively it had longer persistent luminescence time.The luminescence mechanism was also proposed to study the photoluminescence and persistent luminescence process.These results showed that RE~(3+) electronegativities were distinctly important for persistent phosphors and choosing suitable electronegativity codopant was conducive to enhancing the phosphorescent performance.     

焊接热循环参数对大线能量焊接用钢EH40热影响区组织和性能的影响

利用热模拟技术及光学显微镜、透射电镜研究了焊接热循环参数对大线能量焊接用船板钢热影响区组织和性能的影响.发现模拟焊接热影响区组织主要由粒状贝氏体、铁素体和珠光体组成,且随着峰值温度和冷却时间的变化,热影响区的组织发生较大的变化;热影响区的冲击韧性总体水平较高,均在200 J以上,冲击韧性并不随着峰值温度和冷却时间的增加而单调变化;热影响区M-A岛的数量、尺寸、分布和形态影响热影响区的韧性.      

Ultrafine Structure and High Strength in Cold-Rolled Martensite

Structural refinement by cold rolling (10 to 80?pct reductions) of interstitial free (IF) steel containing Mn and B has been investigated from samples with different initial structures: (a) lath martensite, (b) coarse ferrite (grain size 150???m), and (c) fine ferrite (22???m). Unalloyed IF steel with a coarse grain size (120???m) has also included based on a previous study. Deformation microstructures and structural parameters have been analyzed by transmission electron microscopy and electron backscatter diffraction, and mechanical properties have been characterized by hardness and tensile testing. At low to medium strains, lath martensite transforms into a cell block structure composed of cell block boundaries and cell boundaries with only a negligible change in strength. At medium to large strains, cell block structures in all samples refine with increasing strain and the hardening rate is constant (stage IV). A strong effect of the initial structure is observed on both the structural refinement and the strength increase. This effect is largest in lath martensite and smallest in unalloyed ferrite. No saturation in structural refinement and strength is observed. The discussion covers the transformation of lath martensite into a cell block structure at low to medium strains where the driving force is suggested to be a decrease in the dislocation line energy. Medium to large strain-hardening mechanisms are discussed together with structure-strength relationships assuming additive stress contributions from dislocations, boundaries, and elements in solid solution. Good agreement is found between flow stress predictions and stress values observed experimentally both in the initial undeformed martensite and in deformed samples.     

Study on Compound Effect of Bonded Magnets

The compound effect of Nd2Fe14B/Fe3B-Ferrite bonded magnets was studied.The result shows that the value ofβjHC obviously decreases with the ferrite content increasing.In addition, a functional relation between magnetic properties and ferrite content was clearly revealed by the physical relation in the magnetic powders.     

高钢级管线钢的组织特征和强韧性

背散射(EBSD)和扫描(SEM)电子显微镜及力学性能试验表明,微合金化X70、X80和X100管线钢的组织由针状铁素体、粒状贝氏体和少量下贝氏体组成;随钢的有效晶粒尺寸降低、贝氏体含量增加以及组织均匀性提高,高钢级管线钢的强韧性明显增加。     

Experimental charge density distribution and its correlation to structural and optical properties of Sm~(3+) doped Nd_2O_3 nanophosphors

Pure and Sm~(3+) doped Nd_2 O_3 nanophosphors were synthesized using modified Pechini method. The phase formation with symmetry of the sample is confirmed by the Rietveld refinement of the powder Xray diffraction(PXRD) data. The surface morphology and the crystallite size were examined using scanning electron microscopy(SEM) and transmission electron microscopy(TEM) and the results confirmed that the synthesized particles are in nanosize. The energy-dispersive X-ray(EDX) analysis was done to confirm the purity of the sample. The optical properties of the sample were studied using ultraviolet-visible range(UV-Vis) spectroscopic analysis and photoluminescence studies. The calculated band gap of the synthesized Nd_2 O_3 was found to be higher than that of bulk Nd_2 O_3. The photoluminescence(PL) of the prepared samples reveals that doping with Sm3+ ion has influenced the optical properties. Quantitative investigation on charge density distribution was done by analysing the 3-dimensional and 2-dimensional charge density maps drawn along the bonding directions. The maximum entropy method(MEM)/Rietveld analysis was used for the first time to analyse the charge density in the chosen system. Charge density arrangement in the unit cell is correlated to the analysed photoluminescent(PL) properties. The spectral behaviour of the samples has been explained through charge ordering which are verified using experimental data obtained. The studies on these materials have shown that these nanophosphors will provide promising application for near-ultraviolet lightemitting diodes(n-UV-LEDs).