Effect of Cu ion substitution on structural and dielectric properties of Ni-Zn ferrites

A series of Cu-substituted Ni_(0.5-x)Cu_xZn_(0.5)Fe_2O_4(x=0.12,0.16,0.20,0.24 and 0.28) spinel ferrites were prepared by conventional ceramic method to investigate the effects of Cu compositional variation on the structure and dielectric properties.XRD patterns demonstrate that all the samples are crystallized in single-phase cubic spinel structure and the lattice constant increases with increasing Cu content.White grains observed by SEM are Cu-rich phase.The dielectric constant versus frequency curve displays a normal dielectric behavior of spinel ferrites.While the frequency dependence of dielectric loss tangent is found to be abnormal,exhibiting a peak at certain frequency for all Cu-substituted Ni-Zn ferrites.A maximum of the resistivity is observed at x=0.2 due to the decrease of hopping electrons between Fe^(2+) and Fe^(3+) in per unit volume,which is in contrast with the Cu content dependence of dielectric constant and dielectric loss.

Nucleophilic Substitution of Halogenonitrobenzenes by Electrogenerated O_2- on Carbon Gas-diffusion-electrode

Introduction The electrochemical reduction of O;was investigated widely during the past two decades. O;can react with various organic compounds. O;as a new synthesis reagent has been being explored.

Nucleophilic Aromatic Substitution of Nitrobenzenes with Nitrite Ion

It is experimentally found that different renction courses exist when mtrite ion reacts with nitrobenzenes with different electron withdrawing groups. when it is substituted with strong electron withdrawing groups. self-condensation in aprotic polar solvent occurs to give symmnetrical disubstituted diphenyl ethers. However. when it is substituted with moderate electron withdrawing groups, no diphenyl ethers are obtained under the same conditions, instead, corresponding carboxylates are yielded. As a result. the applicability of this reaction is distinctly clarified

Dual strategy of A-site ion substitution and self-assembled MoS_(2) wrapping to boost permittivity for reinforced microwave absorption performance

With the rapid development of electronic technology,how to effectively eliminate electromagnetic pollu-tion has become a serious problem.Perovskite oxides have shown great potential in the field of electro-magnetic wave absorption due to their unique structure and excellent physicochemical properties.Herein,by rationally manipulating the A-site ion substitution strategy,the theoretically directed doping of Sr ions into La ionic sites was utilized and the layered MoS_(2) was loaded by the hydrothermal process to modify its surface.Consequently,the introduced polarization phenomenon improved the dielectric performance of the perovskite oxides,achieving a collaborative dielectric/magnetic loss mechanism.Accordingly,the prepared La0.7Sr0.3FeO3(LSFO)/MoS_(2) as coating filler in the epoxy resin coating system can obtain the minimum reflection loss of-67.09 dB at 1.9 mm and the maximum effective absorption bandwidth of 7.28 GHz at 2.3 mm.More importantly,it also exhibits excellent absorption performance for multi-band electromagnetic waves,covering a wide range of specified frequency bands.It provides inspiration for ex-ploring novel perovskite oxide-based electromagnetic wave absorbing coatings and broadens the choice of ideal candidate materials for designing highly efficient,multi-band absorbers to cope with sophisticated electromagnetic environments.

Photocatalytic Reduction of Cr^Ⅵ by Natural Sphalerite Suspensions under Visible Light Irradiation

The photocatalytic reductive capability of a natural semiconducting mineral, sphalerite has been studied for the first time. The sphalerite from the Huangshaping deposit of Hunan Province performed great photoreductive capability that 91.95% of the Cr^6＋ was reduced under 9 h visible light irradiation, higher than the 70.58% under 9.5 h UV light irradiation. The highly reductive ability results from its super negative potential of electrons in the conduction band. Furthermore, Fe substitution for Zn introduces donor states, and the oxidation process of Fe^2＋ to Fe^3＋ makes it an effective hole-scavenger. Cd and Cu substitute for Zn also reduce the bandgap and help broaden the absorbing edge towards the visible light. These substituting metal ions in natural sphalerite make it a hyper-active photocatalyst and very attractive for solar energy utilization.

VINYL RADICAL POLYMERIZATION INITIATED WITH CERIC ION AND N-(SUBSTITUTED PHENYL) ACETAMIDE SYSTEMS

The polymerization of acrylamide (AAM)in H_2O/DMF or in H_2O/CH_3CN mixed solvent initiated with ceric ion (Ce^(4+) )/N-(substituted phenyl)-acetamide systems have been studied. The redox polymerization was revealed by the low value of overall activation energy (E_α) of AAM polymerization using ceric ion/N-(substituted phenyl) acetamide system as an initiator. The end group of polymer formed was detected by IR spectrum analysis method, it revealed the presence of N-(m-acetoxy-methylphenyl) acetamide (m-AAe) moiety end group in the polymer obtained with ceric ion/m-AAe initiation system.

Raising the capacity of lithium vanadium phosphate via anion and cation co-substitution

The pursuit for batteries with high specific energy provokes the research of high-voltage/capacity cathode materials with superior stability and safety as the alternative for lithium iron phosphate.Herein,using the sol-gel method,a lithium vanadium phosphate with higher average discharge voltage(3.8 V,vs.Li+/Li) was obtained from a single source for Mg2+ and Cl-co-substitution and uniform carbon coating,and a nearly theoretical capacity(130.1 mA h g^-1) and outstanding rate performance(25 C) are acquired together with splendid capacity retention(80%) after 650 cycles.This work reveals that the well-sized anion and cation substitution and uniform carbon coating are of both importance to accelerate kinetic performance in the context of nearly undisturbed crystal structure for other analogue materials.It is anticipated that the electrochemistry comprehension will shed light on preparing cathode materials with high energy density in the future.

Visible light responsive photocatalysts developed by substitution with metal cations aiming at artificial photosynthesis

To solve resource,energy,and environmental issues,development of sustainable clean energy system is strongly required.In recent years,hydrogen has been paid much attention to as a clean energy.Solar hydrogen production by water splitting using a photocatalyst as artificial photosynthesis is a promising method to solve these issues.Efficient utilization of visible light comprised of solar light is essential for practical use.Three strategies,i.e.,doping,control of valence band,and formation of solid solution are often utilized as the useful methods to develop visible light responsive photocatalysts.This minireview introduces the recent work on visible-light-driven photocatalysts developed by substitution with metal cations of those strategies.

Dimensional t-factor variation and increase of stability of the ferroelectric state in(Na_(0.5)Bi_(0.5))TiO_(3)-based solid solutions

The influence of the B-site ion substitutions in(1-x)(Bi_(1/2)Na_(1/2))TiO_(3)–xBaTiO_(3)system of solid solutions on the relative stability of the antiferroelectric(AFE)and ferroelectric(FE)phases has been studied.The ions of zirconium,tin,and(In_(0.5)Nb_(0.5)),(Fe_(0.5)Nb_(0.5)),(Al_(0.5)V_(0.5))ion complexes have been used as substituting elements.An increase in the concentration of the substituting ion results in a near linear variation in the size of the crystal lattice cell.Along with the cell size variation,a change in the relative stability of the AFE and FE phases takes place according to the changes of the tolerance factor of the solid solution.An increase in the tolerance factor leads to the increase in the temperature of the FE–AFE phase transition,and vice versa.Obtained results indicate the way for raising the temperature of the FE–AFE phase transition in(Bi_(1/2)Na_(1/2))TiO_(3)-based solid solutions.

Energy transfer process of Nd^(3+)/Ho3+co-doped fluoride halide glasses with anion substituted multi-wavelength tunable mid-infrared luminescence

Ho^(3+)doped ZBLAN glass with 2.0 and 2.9μm emission was prepared.In order to further improve the luminescence of Ho^(3+),halogen ions(Cl,Br,1)were introduced to reduce the maximum phonon energy and phonon state density of the sample.At the same time,Nd^(3+)was introduced to transfer the energy to Ho^(3+)pumped with a 793 nm laser(Nd^(3+):4 F5/2,4 F3/2→Ho^(3+):5 I6).The effect of different halogen ion on the luminescent properties of the fluoride halide glass was compared.The results show that the luminescent intensity of infrared increases with the introduction of different halogen ions.By comparison,it is found that the sample with I-has the strongest luminescence of 1064 nm,2.0μm and 2.9μm.This is consistent with the calculated J-O intensity parameters.In addition,the 2.0 and 2.9μm emission of Ho^(3+)pumped with a 450 nm laser will not disappear.A mid-infrared sample with multi-wavelength excitation and multi-wavelength emission can be obtained.Nd^(3+)/Ho^(3+)co-doped fluoride halide glasses with 1064 nm,2.0μm and 2.9μm luminescence were prepared by melt quenching method.The luminescent mechanism and the energy transfer process between the two ions of Nd^(3+)/Ho^(3+)co-doped fluoride halide glass were studied.The J-O parameters,luminescence lifetime and absorption emission cross-sectional area of Ho^(3+)and Nd^(3+)were calculated,respectively.It is found that the value ofΩ2 in the glass matrix increases with the introduction of different halogen ions,whileΩ4 andΩ6 do not change obviously in different glass compositions.This is because the environment of the crystal field around the rare earth ions changes.The crystal phase and phonon energy of the sample were analyzed by X-ray diffraction pattern and a Fourier transform infrared spectrometer,respectively.Based on the above spectra and data(phonon energy is 634.71 cm-1),it can be predicted that Nd^(3+)/Ho^(3+)co-doped fluoride halide glass is a potential mid-infrared luminescent material.

Efficient Near-infrared Down-conversion Phosphor of Ce^(3+)/Yb^(3+)Co-doped La3Ga5SiO14 and Its Spectral Structural Modulation

A series of near-infrared(NIR)down-conversion phosphors of La_(3)Ga_(5)SiO_(14)(LGS):Ce^(3+)/Yb^(3+)were synthesized via high-temperature solid-state reaction.Under excitation at 345 nm,the phosphors show strong NIR emission around 978 nm,which matches well with the optimal spectral response of crystalline silicon(c-Si)solar cells.The emission spectra and decay curves were used to demonstrate the energy transfer from Ce^(3+)to Yb^(3+).The energy transfer mechanism was discussed in detail,indicating that the energy transfer from Ce^(3+)to Yb^(3+)is dominated by a single photon process,and the energy transfer efficiency is up to 51%.In addition,La_(3)Ga_(5-z)Al_(2)SiO_(14)(z=0,1,2,3):Ce^(3+)/Yb^(3+)were also synthesized.The NIR emission intensity of La_(3)Ga_(2)Al_(3)SiO_(14):1%Ce^(3+)/5%Yb^(3+)is 4.6 times that of LGS:1%Ce^(3+)/5%Yb^(3+),and the thermal relaxation was used to explain this phenomenon.The results show that La_(3)Ga_(5-z)Al_(2)SiO_(14)(z=0,1,2,3):1%Ce^(3+)/5%Yb^(3+)phosphors have the potential to increase the conversion efficiency of c-Si solar cells.

B-site substituted solid solutions on the base of sodium-bismuth titanate

The paper presents results of studies of the formation of phases during the solid-state synthesis in the[(Na_(0.5)Bi_(0.5)T_(0.80)Ba_(0.20)]Ti_(1-y)B_(y)TO_(3)system of solid solutions with B-site substitutions.The substitutions by zirconium,tin and ion complexes(In_(0.5)Nb_(0.5)T and(Fe_(0.5)Nb_(0.5)T have been studied.It has been found that the synthesis is a multi-step process associated with the formation of a number of intermediate phases(depending on the compositions and calcination temperatures).Single-phase solid solutions have been produced at the calcination temperatures in the interval 1000–1100℃.An increase in the substituting ions concentration leads to a linear increase of the crystal cell size.At the same time,the tolerance factor gets reduced boosting the stability of the antiferroelectric phase as compared to that of the ferroelectric phase.

Analysis of the linkage positions and isomers of monosaccharide units in oligosaccharides by negative secondary ion mass spectrometry in combination with the stereoselective reaction with substituted boronic acid

The negative secondary ion mass spectrometry,in combination with the stereoselective derivatizations with substituted boronic acid RB(OH)_2,was used in the analysis of fourteen oligosac- charides.The mass spectra of the derivatives provide information on their linkage Positions and iso- merism of the individual monoscaccharide units.The results indicated that among the derivatives of the oligosaccharides analyzed,those with 1—4 and 1—6 linkages all presented the ion peaks at m/z 287,sometimes one more peak at m/z 449.Furthermore,a relationship was found between the linkage positions and the intensity orders of the derivative ions.Finally,the derivatives of the disaccharides with a galactose presented an intense ion peak at m/z 347,and those of oligosaccharides with 1—6 linkage to a galactose at terminal presented the ion at m/z 317.In the case of oligosaccharides with a fructose residue,characteristic ion of m/z 155 was produced.The conditions of stereoselective derivatizations and mass spectrometry were studied,in order to obtain a better reproducibility of the mass spectra.

Cytocompatible 3D chitosan/hydroxyapatite composites endowed with antibacterial properties:toward a self-sterilized bone tissue engineering scaffold

Bone tissue scaffolds based on bioactive polymer–hydroxyapatite composites have caused infections that seriously limit their extended application. In this study, we proposed a practical ion substitution method to synthesize in situ silver phosphate on the surface of a two-level, threedimensional chitosan/nano-hydroxyapatite scaffold. A release test of silver ions in a phosphate buffered saline(PBS) solution was performed to demonstrate that silver ions were released continuously from the silver phosphate during the initial 6 days of the study. The antibacterial property and cytocompatibility of the scaffolds treated with different concentrations of silver nitrate solution were assessed by in vitro assays with Escherichia coli and MC3T3-E1, respectively. The ability of the silver-containing scaffolds to induce bacteriostasis was confirmed by the inhibition zone(15 mm) and high bactericidal rate([99 %). Cell proliferation, morphology and the alkaline phosphatase activity of MC3T3-E1 cultured on the scaffold with low silver phosphate contents were comparable with those cultured on control samples.