查看更多>>摘要：In this study,a class of rare earth composite sandwich phthalocyanines(MPcs,M=La,Y,Yb,Sc)were prepared and compounded with graphene and carbon nanotubes to obtain MPc/Gr and MPc/CNTs composites.The electrocatalytic behaviors of MPc/Gr and MPc/CNTs electrodes were further investigated.The results show that the central rare earth metal has a large influence on the electrocatalytic perfor-mance.For the MPcs/Gr samples,ScPc with the smallest ionic radius and molecular size can be more uniformly dispersed in graphene,and the hydrogen precipitation overpotential of ScPc/Gr electrode is 514 mV,corresponding to a Tafel slope of 148 mV/dec,with better electrocatalytic performance than other rare earth metal phthalocyanines.As for the MPc/CNTs composites,LaPc,which has the largest ionic radius and molecular size,is more uniformly dispersed on the surface of CNTs,so that the LaPc/CNT electrode exhibits the best LSV performance with the smallest corresponding Tafel slope(176 mV/dec).The main reason is the different binding modes of MPcs molecules in Gr and CNTs.When rare earth phthalocyanine is combined with layered graphene,the smallest size of rare earth phthalocyanine(ScPc)is more easily embedded in the graphene layer,resulting in better homogeneity of the composite,larger effective contact area and better electrocatalytic performance.In contrast,when rare earth phthalocy-anine is bound to carbon nanotubes in a tubular structure,it is mainly bound by attaching to the surface or being entangled by the carbon nanotubes.In this case,the rare-earth phthalocyanine molecules(LaPc)with larger layer spacing can provide more contact area with CNTs,forming a more uniform and effective composite,which eventually provides more active sites and better electrocatalytic performance.
查看更多>>摘要：In order to analyze the influence of the addition of yttrium and manganese on the soot combustion performance and high temperature stability of CeO2 catalyst,a series of Y/Mn-modified CeO2 catalysts were prepared.The effects of structural properties,textural properties,oxygen vacancies,Ce3+,surface adsorbed oxygen species,reduction properties and desorption properties of oxygen species on the ac-tivity were analyzed by various characterization methods.The results of the activity test show that the addition of manganese is beneficial to enhancement of the activity,while the addition of yttrium in-creases the amount of reactive oxygen species,but decreases the activity.After aging at 700 ℃,the activity of the CeMn catalyst decreases most sharply,while the catalytic activity of the CeY catalyst can be maintained to a certain extent.Interestingly,the addition of yttrium and manganese at the same time can stabilize the activity.The fundamental reason is that yttrium and manganese move to the surface of the solid solution after aging,which increases the reduction performance of the catalyst,thus contrib-uting to the increase of activity.Although the activity of CeYMn catalyst decreases after aging at 800 ℃,it is still higher than that of other catalysts aged at 700 ℃.
查看更多>>摘要：Usually it is generally believed that the Er element forms the Er2Fe14B phase,which will seriously deteriorate the magnetic properties.Distinctly,here we report the balance of corrosion resistance and coercivity in Nd-Fe-B sintered magnets through using simple Er30Cu70 additive whose price is much lower than Dy and Tb.By reasonably controlling Er30Cu70 addition,the corrosion resistance is improved at the minimum limit of reducing the magnetic properties.Through studying the influence mechanism of Er element,it is found that the main effect of Er elements is to replace the Nd elements at the edge of the main phase grains to form a(Er,Nd)2Fe14B shell with low HA,resulting in the reduction of magnetic properties.The improvement of corrosion resistance mainly comes from the more stable Cu element introduced at the grain boundary.At the same time,the target magnets also show different advantages under different heat treatment methods.Above findings may spur progress towards developing the low-cost permanent magnets that rival the commercial Nd-Fe-B counterpart.
查看更多>>摘要：A simple composite Sr1-xNdxMnO3(x=0,0.05,0.1,0.15,0.2)nano powders were successfully prepared by the sol-gel method as a light-weight broadband electromagnetic wave absorber.The effect of Nd3+doping on the structure,microstructure and properties of SrMnO3 was investigated.It is found that with the doping of Nd3+,the space group of the SrMnO3 changes from p63/mmc to pm3m,and the crystalline shape starts to change from hexagonal to cubic crystalline.Scanning electron microscopy(SEM)and Brunauer-Emmett-Teller(BET)tests confirm that the particle sizes of the sample decrease and the specific surface area increases,which are attributed to the inhibition of grain growth after Nd3+is doped.X-ray photoelectron spectroscopy(XPS)shows that after Nd3+doping,the content of oxygen vacancy increases,and Mn4+converts to Mn3+.Due to the defects of the materials,the polarization effect is enhanced,thus,the dielectric and magnetic properties of the doped samples are improved.The maximum reflection loss of the Sr0.85Nd0.15MnO3 is-33.41 dB at 7.84 GHz for a thickness of 2.4 mm,while Sr0.9Nd0.1MnO3 has the best bandwidth performance at 2.32 GHz with a reflection loss below-10 dB.
查看更多>>摘要：The present study is a systematic effort to investigate the structure-sensitive magnetic parameters of Ce3+substituted Ba-Sr hexaferrite nanocrystals chemically formulated as Ba0.5Sr05CexFe12-xO19 where x=0.0-0.2 with △x=0.05.The hexaferrite powders were prepared using the sol-gel self-ignition route and structurally characterized by means of powder X-ray diffraction and Fourier transform infrared spectroscopy.The creation of the M-type hexaferrite phase within the synthesized samples was revealed from the Rietveld refinement of the X-ray diffractograms.The occurrence of a secondary phase of CeO2 was revealed within the hexaferrites for the substitution,x＞0.The refined X-ray diffraction data were utilized to compute the lattice parameters,X-ray density,and lattice parameter ratio.The crystal structure plotted from the refined XRD data reveals the occupancy of the ions at different lattice sites.The XPS data of the hexaferrite were analyzed to confirm the oxidation states of the constituent ele-ments.The nanocrystalline nature of the hexaferrites was revealed from the crystallite sizes calculated using Scherer's formula.The analysis of FTIR spectra confirms that only a fraction of Ce3+accommodated in the lattice and the remaining Ce content reside in the form of the CeO2 phase.The morphology of the hexaferrites was analyzed from the FESEM profiles of the ferrite samples.The magnetic behavior study was performed by analyzing the Curie temperature,hysteresis loops,and hyperfine interactions by means of susceptibility,V.S.M,and Mössbauer spectroscopy,respectively.The hexaferrites with increasing coercivity,decreasing saturation magnetization,and decreasing Curie temperature are re-ported in the study.The substituted Ce3+ions inhibit the grain growth and create lattice imperfections giving rise to hexaferrites with tuned magnetic parameters suitable for different applications.
查看更多>>摘要：In this work,the magnetic,dielectric properties and electric modulus of Ce3+substituted cobalt-magnesium(Co0.7Mg0.3CexFe2-xO4)(labeled as CMCF)ferrite nanoparticles were investigated in detail.Saturation magnetization decreases from 50.05 to 34.87 emu/g for further substituting Ce3+ions.Meanwhile,coercivity increases from 738.22 Gs for the CMCFO sample to 912.10 Gs for the CMCF2 sample,then decreases monotonically to 762.1 Gs for the CMCF5 sample.The cerium content and particle size play important roles in controlling the magnetization and coercivity of the CMCF nanoparticles.All CMCF nanoferrites are suitable for microwave applications since their high-frequency response ranges from 7.72 to 11.07 GHz.The CMCF nanoferrites'dielectric parameter dispersion exhibits normal behavior.The pristine Co-Mg nanoferrite only has ε'value of 28.25,but the nanoferrite MCMF2 has ε'value of 365.03,with an enhancing ratio of 1192％.The conduction mechanism of the MCMF nanoferrites was determined by fitting the σac results via the Jonscher power law.At 653 K,large polaron tunnelling is thought to be responsible for this conduction process,which is followed by electron barrier hopping at higher temperatures.Cole-Cole diagrams at different temperatures,assuring the contributions of the grains and their boundaries at lower temperatures(653 K)and only the grains at higher temperatures.Based on our results,the CMCF nanoferrites hold magnetic and semiconducting nature,which can be used in magnetic devices and dielectrics in lower-frequencies or conductors in higher-frequencies.
查看更多>>摘要：The main focus of this work is to study the effect of the ionic radius of different rare earth dopant cations RE3+(RE=La,Sm,Dy,and Ho)on structural and various physical properties of sodium bismuth titanate(Na0.5Bi0.5TiO3,NBT)based perovskite nanomaterials.The X-ray diffraction data indicate the successful formation of the rhombohedral phase(space group R3c)of NBT nano perovskite incorporated with various rare earth ions in Bi-site.The lattice parameters were found to increase linearly with the ionic radius of the dopant cation.The ionic radii and atomic mass of rare earth dopants appear to be essential factors in the grain growth of the prepared compositions.The grain growth results in better crystallinity of the sample by reducing the microstrain with the increase of dopant ionic radius.Field emission scanning electron microscopy and energy-dispersive X-ray spectra confirm the prepared compositions'phase purity and stoichiometry.The UV-Vis spectra reveal that La-doped NBT composition exhibits the lowest optical band gap,which unfolds the application of NBT-based perovskite as photoactive material.The ac conductivity and complex impedance spectra unveil that the composition with the largest ionic radius,i.e.,La-doped NBT compound,exhibits the highest dc and bulk conductivity with the lowest activation energy.The frequency-dependent dielectric data follows Havriliak-Negami(HN)formalism and non-Debye type relaxation phenomena.Results also indicate that La-doped NBT composition ex-hibits the highest dielectric strength value.Thus,this study first elaborates that the increasing ionic radius of the rare earth dopant cation in the Bi-site of NBT perovskite improves its microstructural,optical,and electrical properties.
查看更多>>摘要：Although solid-state lithium electrolytes have the potential to reduce the safety issues associated with organic liquid electrolytes,disadvantages such as low total conductivity,large interface impedance,and delamination of the interface due to cyclic stress still need to be addressed.The solid-state lithium-ion conductor Li0.33La0.56TiO3(LLTO)was prepared via a hydrothermal route by using CTAB as templates in this paper.Perovskite LLTO with micro-porous channels was obtained and the total conductivity is comparable to the non-porous LLTO.Porous LLTO pellets are infiltrated with the non-porous LLTO pre-cursor solution,and the total conductivities of the infiltrated porous LLTO are all higher than those without infiltration.After infiltration,the porous LLTO calcined at 600 ℃ achieves the highest total conductivity,7.88 × 10-5 S/cm.The fracture toughness of the infiltrated LLTO is higher than that of the non-porous LLTO.The results demonstrate a new way to prepare solid-state lithium-ion conductors with high ionic conductivity and great tolerance to cyclic stress.
查看更多>>摘要：We hereby report the room-temperature structural and optical characterization of RECr0.85Mn0.15O3(RECMO,RE=Ho,Gd and Pr)compounds synthesized by the auto-combustion sol-gel route.Their low temperature dielectric properties are also presented.The RECMO compounds crystallize in an ortho-rhombic Pbnm symmetry with an average grain size range of 51-80 nm.Structural analysis reveals an increase in the structural distortion compared to that of the undoped bulk compounds.Optical mea-surements exhibit a significant reduction in bandgap values for RECMO nanoparticles when compared with their undoped bulk compounds.Further,from the absorbance measurements various optical pa-rameters such as skin depth,extinction coefficient,refractive index and optical conductivity were also calculated.The dielectric analysis confirms the lower values of the dielectric permittivity and dielectric loss than those of their corresponding bulk compounds.AC conductivity versus frequency and tem-perature data are fitted according to the Jonscher's power law and Arrhenius law,respectively.The small polaron hopping is responsible for the electric conduction in these compounds.The tunability of the optical and dielectric properties as a result of substitution and particle size reduction makes these materials useful for various potential applications in photocatalysis,optoelectronics and low permittivity dielectrics.
查看更多>>摘要：To find a greener and more economical approach for treating the Mountain Pass rare earth concentrate(MPREC),a novel"Combination Method",including the processes of oxidizing roasting,HCl leaching and sulfuric acid roasting,is proposed in this research.In this paper,the effect of phase transition behavior in hydrochloric acid leaching during oxidative roasting at 450-600 ℃ was studied.During roasting,the bastnasite in MPREC is decomposed into CeLa2O3F3 and(Ce0.33,La0.33,Ca0.33)O1.5.As the CeLa2O3F3 phase has the fluorine-fixation effect,the generated CeLa2O3F3 phase can not be dissolved by HCl after roasting at 500 and 550 ℃,but it can be decomposed by HCl after roasting at over 600 ℃,resulting in the improvement of the leaching rate of total F element.The maximum leaching efficiency of rare earth elements(REEs)can reach 70.32 wt％at the roasting temperature of 550 ℃.After roasting at over 600 ℃,some F-ions in the solution combined with RE3+to form REF3 precipitate and enter the leaching residue,and the others are in the form of[CeF3]+in the leaching solution during leaching,therefore,the leaching efficiency of non-cerium REEs decreases while that of cerium element increases.This work provides basic research for optimizing the actual production process of MPREC.
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