Synthesis and characterization of La NixCo1–xO3: Role of microstructure on magnetic properties

Perovskite-type structures with the composition La Ni x Co1–x O3(x=0.3, 0.5, 0.7) were synthesized by a modified sol-gel method. Using transitional metal elements on the lanthanum base perovskites, properties could be tuned by doping the structure. Thermogravimetric analysis(TGA) evidenced a temperature of 350 °C as the start point of the perovskite-phase formation. Scanning electron microscopy(SEM) images showed the microstructure changes(grain size) of the cobalt-doped perovskite due to composition. In addition, it was shown that magnetic properties of the samples were dependent of cobalt content; experimental results pointed to the existence of disordered spins interactions, which were more evident with the decrease of cobalt content and the existence of ferromagnetic coupling among spins of the samples. These results showed the feasibility of producing a family of compounds with the desired properties, manipulating composition and therefore the microstructure.     

Effect of Yb2O3 additives on structure and transport properties of YBa2Cu3O7-δ

The effects of Yb2O3 particles on the microstructure and transport properties of YBa2Cu3O7-δ(YBCO) were investigated through resistance-temperature(R-T),scanning electron microscope(SEM),X-ray diffraction(XRD) and the critical current density(Jc) versus applied magnetic field(Jc-B) measurements.YBCO powder with Yb2O3 additives was synthesized using standard solid state reaction technique.Rietveld refinements of X-ray diffraction showed that both Yb2O3 and YBCO phases coexisted in the products.The critical current density(Jc) exhibited a maximum at x=0.05 in YBCO+xYb2O3 systems.Moreover,small additions of Yb2O3 in YBCO could enhance Jc by applying the magnetic field,although the superconducting temperature(Tc) decreased monotonically with increasing additive content.The characteristic behavior of Jc might come from the counterbalance of two effects simultaneously,which was caused by the inhomogeneity of grains distribution in nano-scale and degradation on superconducting properties.     

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...     

High-frequency magnetic properties of biphase Ce2Fe17N3/α-Fe microflakes with easy-plane anisotropy

Soft magnetic composites(SMCs) are effective as magnetic powder cores in an inductor.Due to high saturation magnetization,large magnetocrystalline anisotropy and high operating frequency of M(metal)-RE(rear earth) soft magnetic composites,it is possible to miniaturize inductor cores by reducing total loss,especially eddy current loss and excess loss at high frequencies.In this article,the characteristics of Ce₂Fe₁₇N₃/α-Fe(CFN/F) loss per volume and effective perm...     

Effects of magnetic annealing on crystallization and magnetic properties of Nd2Fe14B/α-Fe nanocomposite magnets

Crystallization and magnetic properties of Nd2Fe14B/α-Fe nanocomposite magnets have been investigated by annealing the as-spun ribbons with magnetic field.The crystallization process was accelerated by field annealing.The hysteresis loop became to be fat by magnetic annealing at 645 oC for 4 min,which was 690 oC for ribbons annealing without magnetic field.The relative content of α-Fe phase was increased from the results of XRD.The strength of the magnetic field had no obvious influence on the remanence and coercivity,but modified the squareness of hysteresis loop.     

Catalytic combustion of toluene on Pt/Al2O3 and Pd/Al2O3 catalysts with CeO2,CeO2-Y2O3 and La2O3 as coatings

CeO₂,La₂O₃,and CeO₂-Y₂O₃ oxides were coated on the surface of spherical granular AI₂O₃(3-5 mm)through impregnation method,and proved as better supports of Pd and Pt catalysts.The influences of rare earth metal doping on the adsorption rates of Pd and Pt ions,as well as the catalytic performance,were investigated.Results show that the H₂PtCl₆·6H₂O adsorption rates of the Al     

Effects of manganese substitution on magnetic and magnetostrictive properties of Tb0.5Dy0.5(Fe1-xMnx)1.92/epoxy composites with spherical single-crystal particles

Spherical Tb_0.5Dy_0.5(Fe_1-xMn_x)_1.92(x=0,0.05,0.10 and 0.15) single-crystal particles were prepared.The magnetic anisotropy of the alloy decreases as x increases from 0 to 0.15.Subsequently,we prepared giant magnetostrictive composites with these spherical Tb_0.5Dy_0.5(Fe_1-xMn_x)_1.92 single-crystal particles.As a consequence,well <111>-orie nted Tb_0.5Dy_0.5(Fe_1...     

Controlled synthesis and luminance properties of lanthanide-doped β-NaYF4 microcrystals

Hexagonal Yb3+,Er3+-doped Na YF4 crystals with different morphologies were synthesized by a facile hydrothermal method at 140–200 oC. Their shape and size could be controlled by varying hydrothermal temperature, time and doping effect of Ce3+ ions. Interestingly, the products displayed hexagonal sheet, plate, crown-like prism to tube changes in the temperature range from 140 to 200 oC. A combination of diffusion-controlled growth and selective adsorption was proposed to understand the formation of the Na YF4 crystals with well-defined shapes. Na YF4:Yb3+/Er3+ crystals exhibited shape-dependent up-conversion(UC) luminescence under excitation of 980 nm, and their luminescence property could be tuned by doping Ce3+ ions.     

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...     

Tailoring effect of Y2O3 on water resistance of Na2O-ZnO-Al2O3-B2O3 glasses

To explore the improving effect of Y₂O₃ on the water resistance of xY₂O₃-(100-x)(0.05 Al₂O₃-0.15 ZnO-0.15 Na₂O-0.65 B₂O₃)(x=0,0.7 mol%,1.4 mol%,2.1 mol%,2.8 mol%) glasses,glass structure and ion migration characteristics were respectively characterized by an infrared spectrometer and an electrochemical workstation.X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive Xray spect...     

Sol-gel synthesis,surface and magnetic properties of nanocrystalline SmAlO3

Nanocrystals of single-phase samarium monoaluminate (SmAlO3) were synthesized and studied for the first time. Malic acid was employed as a new complexing agent in the sol-gel process. The material was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDS), specific surface area and density. The lowest size of the nanoparticles was about 50–60 nm and some of them formed agglomerates. The binding energies of core-level electrons of Sm (3d, 4d, 4f, ...     

Effect of synthesis conditions and surrounding medium on luminescence properties of YVO4:Eu3+nanopowders

Nanocrystalline yttrium vanadate doped with europium ions powders were synthesized via sol-gel method based on decomposition of metal-polymer complex. X-ray diffraction analysis showed that samples had pure tetragonal phase without any impurities. Scanning electron microscopy and static light scattering technique were used to study morphology and size of prepared nanoparticles. Average diameter of the nanoparticles was about 40 nm. The changes in structural and luminescence properties were observed as a function of the first and second calcination temperature. The optimal conditions for synthesis of nanoparticles were determined as Т1=500 °С, t1=1 h; Т2=950 °С, t2=1.5 h. The effect of different media surrounding the nanoparticles on their luminescence properties and lifetime was investigated and discussed in terms of effective refractive index. It was found that the observed lifetime of YVO4:Eu3+ 5 at.% nanophosphor was decreased from 0.64 ms in air(nmed=1) to 0.45 ms in chalcogenide glass As39S61(nmed=2.39).     

Magnetic properties and magnetic entropy change of perovskite manganites La_(0.9-x)Eu_xSr_(0.1)MnO_3(x=0.000,0.075) by experimental method and numerical fitting

Polycrystalline samples La_(0.9-x)EuxSr_(0.1)MnO_3(x = 0.000, 0.075) were prepared by the standard solid-state reaction method. The results show that the samples preform a characteristic of clusters spin-glass state at low temperature. The samples show a characteristic of ferromagnetism(FM) characteristic in the temperature range of 15-125 K and 15-150 K respectively; the samples show preformed clusters in the temperature range of 125-343 K and 150-325 K, respectively, the samples show paramagnetism(PM)characteristic above 343 and 325 K, respectively. The second-order transitions are found at 118 and 135 K for undoped and doped sample, respectively. When the applied magnetic field is 7 T, the maximum magnetic entropy change |△S_M| value of the samples is near the Curie temperature(Tc), and the value of|△S_M| reaches 2.76 and 3.03 J/(K kg), respectively. In addition, the relative cooling power(RCP) is found to be 425.28 and 443.53 J/kg. The numerical fitting data fit well with experimental data. These results indicate that both the samples have the potential to realize magnetic refrigeration in the high temperature region(T 77 K).     

Electrochemical synthesis,structure characterization and magnetic properties of Tb_xFe_7Co_3(x=0,0.6,0.8) nanowires

Highly ordered Tb_xFe_7 Co_3(x=0,0.6,0.8) nanowires were synthesized in alumina templates by electrochemical deposition method.Here,the effects of Tb content and annealing treatment on the phase composition,morphology,crystalline structure and magnetic properties were investigated.The asdeposited Tb_0 Fe_7 Co_3 nanowires comprise Fe_7 Co_3 phase.While after adding Tb,the diffraction peaks slightly shift left,indicating the infiltration of Tb atoms into Fe_7 Co_3 phase.After annealing,Tb_0 Fe_7 Co_3 nanowires still consist of Fe_7 Co_3 phase with a slight enhancement on coercivity.While the annealed nanowires with Tb doped present a complex phase composition containing Fe3 Tb,Fe_2 Tb,Co_3 Tb,Co_(17)Tb_2,TbFeO_3 and Fe_2 O_3 phases distribute in the central portion,and Co_(0.72)Fe_(0.28) at the nanowire outer walls.The annealed Tb_xFe_7 Co_3(x=0.6,0.8) nanowires show higher magnetic performance owing to the formation of hard magnetic phases,the interfacial elastic coupling between hard and soft phases and the coherent Fe3 Tb/Co_3 Tb interface which restrain the domain wall motion.To be specific,the coercivity and remanence ratio of TbxFe_7 Co_3(x=0.6,0.8) nanowires significantly enhance with increasing Tb content.     

Structure,magnetism and magnetic thermal properties of heavy rare earth Tb_(1-x)Tm_xFeO_3(x=0.00,0.15,0.25) polycrystalline samples

Tb_(1-x)Tm_xFeO_3(x = 0.00,0.15,0.25) polycrystalline series were synthesized using a solid-state reaction.Our results show that all three prepared samples are in a distorted orthogonal structure and their space group is pbnm.When the Tm~(3+)doping amount increases,the characteristics of the spin-flip of the sample decreases following an initial increase at the beginning;the antiferromagnetic property almost reaches zero;the magnetization decreases at the beginning but increases later on.The maximum magnetic entropy change and magnetic refrigeration effect RCP are reduced at varying degrees.Under a 7 T magnetic field,the maximum magnetic entropy change,△S_(max),for the three samples of Tb_(1-x)Tm_xFeO_3 with x=0.00,0.15,0.25 is 13.78,-9.28,and 10.69 J/(K·kg),respectively;the magnetic refrigeration capacity(RCP) is 316.85,175.2,and 297.60 J/kg,respectively.In summary,doping with the element Tm reduces △S_(max) and RCP of the sample.Since the maximum magnetic entropy change and the cooling capacity for the three samples are relatively large,they can be used as an alternative for magnetic refrigerants.     

CO2 sensing properties and mechanism of PrFeO3 and NdFeO3 thick film sensor

The CO_2 sensing of PrFeO_3 and NdFeO_3 sensors were investigated. Experimental results show that the resistances for PrFeO_3 and NdFeO_3 in CO_2 gas are larger than those in air and the responses for PrFeO_3and NdFeO_3 sensors increase with an increase in room-temperature relative humidity. When exposed to1000 ppm CO_2, the response of PrFeO_3 thick film based on nano-powders annealed at 700℃can reach8.44 at 160℃for the background of wet air with 58%of room-temperature relative humidity (RH),which is much larger than the corresponding value (3.03) in wet air with 25%RH. The sensing response S of NdFeO_3 thick-film sensor based on nano-powders annealed at 600℃to 3000 ppm CO_2 at the operating temperature 200℃can reach 2.36 for the background of wet air with 72%RH, which is larger than the corresponding value (1.83) in the air with 25%RH. Compared with other CO_2 sensing materials, the PrFeO_3 sensor has larger response at lower operating temperature for CO_2 gas and may be used as a new CO_2 sensing material.     

Enhanced magnetic properties of Ce17Fe76.5Co1Zr0.5B6 alloys by magnetic field heat treatment

In the present work, Ce₁₇Fe_76.5Co₁Zr_0.5B₆ ribbons were prepared by a direct melt spinning method. The effects of chamber pressure and magnetic field annealing temperature on the magnetic properties and microstructures of the alloys were investigated. The grain size and content of Ce₂Fe₁₄B phase can be changed by adjusting the chamber pressure, and the optimal magnetic performance is obtained at 0.04 MPa. The magnetic properties can be influenced under magnetic field heat treatment. When the annealing temperature is lower than the Curie temperature, the refinement and a uniform distribution of the grains is obtained. The irreversible magnetic susceptibility curve reveals that magnetic field heat treatment enhances the exchange coupling interaction between grains of the Ce₂Fe₁₄B phase. When the magnetic field annealing temperature is 438 K, the alloy displays the optimal magnetic properties. Compared with the as-spun sample, the values of intrinsic coercivity (H_ci), remanence (B_r) and maximum energy product ((BH)_max) increase by 3.4%, 9.8% and 18.7%, respectively. This work provides an effective approach by which to enhance the magnetic properties of Ce–Fe–B alloys.     

Effects of Sm-doping on microstructure,magnetic and microwave absorption properties of BiFeO_3

In this paper,polycrystalline samples of Bi_(1-x)Sm_xFeO~3(x=0,0.05,0.1,0.15) were successfully synthesized by sol-gel method.The effects of Sm concentration on the crystal structure,morphology,chemical states,magnetic properties and microwave absorption performance were studied by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),a vibrating sample magnetometer(VSM) and a Vector network analyzer(VNA),respectively.The results show that the rare earth Sm doping causes the crystal structure to change.When x≤0.1,Bi_(1-x)Sm_xFeO_3 is the distorted rhombohedral structure with space group R3 c.With the increase of Sm doping amount to x=0.15,the phase structure of Bi_(1-x)Sm_xFeO_3 changes from rhombohedral structure to cubic structure with the space group Pm3 m.The particle size decreases with the increase of the Sm doping amount.The analysis results show that Sm doping can effectively reduce the oxygen vacancies and significantly improve its magnetic properties.The results exhibit that moderately doped rare earth Sm element can effectively improve microwave absorption properties of Bi_(1-x)Sm_xFeO_3 powders.When Sm doping amount of x is 0.1,the Bi_(0.9)Sm_(0.1) FeO_3 compound has good microwave absorption performance,and the minimum reflection loss value of Bi_(0.9)Sm_(0.1)FeO_3 powder reaches about-32.9 dB at11.7 GHz,and its effective absorption bandwidth(RL -10 dB) is 2.6 GHz with the optimal matching thickness of 2.0 mm.     

Reordering kinetics and magnetic properties of mechanically disordered nanocrystalline Ll2-type Ni3Al + Fe alloys

The paramagnetic disordered high temperature states of Ll₂ or γ′-Type Ni₃AlFe alloys become ferromagnetic at low temperatures if retained in metastable disordered (γ) state. Using mechanical attrition (milling) which also transforms the material into nanocrystalline form, various Ni₃AlFe alloys have been prepared in metaastable-γ form and their magnetisations M(γ) and M(γ′) and Curie temperatures T_c(γ) and T_c(γ′) measured. Fe atoms possess a giant magnetic moment in these alloys and polarise neighbouring Ni atoms but this polarisation effect is lower in the disordered state due to a lower number of FeNi nearest neighbours resulting in M(γ) < M(γ′) and T_c(γ) < T_c(γ′). Currently available expressions for magnetic ordering energies based on Bragg-Williams nearest neighbour interactions are found to be inadequate for these giant-moment-type alloys. Isothermal ordering kinetics of the metastable-γ-state which is also nanocrystalline indicate that the ordering reaction cannot propagate across the disordered nanograin boundaries and each grain must obtain its own γ′ nucleus. This results in a Johnson-Mehl-Avrami exponent n ≈ 1.     

Impact of La3+ substitution on electrical,magnetic, dielectric and optical properties of Ni0.7Cu0.1Zn0.2LaxFe2–xO4 (0 < x < 0.035) system

The oxalate co-precipitation method was used to synthesize the La³⁺ substituted Ni–Cu–Zn (La–NCZ) nanoferrites having chemical composition Ni_0.7Cu_0.1Zn_0.2La_xFe_2–xO₄ (x = 0, 0.015, 0.025 and 0.035). DC resistivity study of nanoferrites shows both the conducting and semiconducting behaviour. The room temperature DC electrical resistivity of Ni–Cu–Zn (NCZ) nanoferrites decreases, whereas Curie temperature increases with increasing La³⁺ content. In the temperature range of 30–170 °C nanoferrites show p-type semiconducting behavior except x = 0.015; thereafter, they show n-type behaviour. The frequency dispersive initial permeability (μ_i) associated with its real and imaginary (μ′ and μ") parts are attributed to the domain wall movement and magnetic spin resonant. The μ_i, μ′ and μ" of La–NCZ nanoferrites are higher than those of pure NCZ nanoferrite. Dielectric constant (ε′), dielectric loss (ε″) and AC resistivity (ρ_AC) of La–NCZ nanoferrites show normal dielectric behaviour. It is found that ε′ of NCZ nanoferrites decreases with the increasing content of La³⁺ ions. The bandgap energy of La–NCZ nanoferrites is achieved in the range 1.36–1.70 eV confirming the semiconducting nature of materials.