水热合成单分散球状ZnxCd1-xS及其光催化性质

采用简单的水热合成路线制备高产量单分散球状ZnxCd1-xS,通过X射线衍射、扫描电镜以及紫外-可见漫反射对所得的产物进行表征。结果表明,所得产物呈现六方相纤锌矿结构,并且ZnxCd1-xS产物呈现出很好的均匀性与规则性。采用光催化降解罗丹明B反应来评价ZnxCd1-xS的光催化活性。其中,Zn0.4Cd0.6S具有最高的催化活性,并且在降解反应过程中表现出很高的稳定性。     

Investigation on the synthesis and quantum confinement effects of pure and Mn added Zn(1−x)CdxS nanocrystals

Zn_(1−x)Cd_xS and Zn_(1−x)Cd_xS:Mn²⁺ semiconductor quantum dots (2-4 nm) have been prepared by a novel solvothermal route assisted microwave heating method. The growth parameters governing the smaller size and higher yield have been optimized. The synthesized QDs exhibit a significant blue shift as compared to their corresponding bulk counterpart in the UV-vis optical absorption spectrum. The dielectric constant value varies from 2.79 to 6.17 (at 40 °C, 1 kHz) depending upon the composition of the alloy; lower value corresponds to Zn_0.75Cd_0.25S:Mn²⁺ and the higher value corresponds to Zn_0.25Cd_0.75S:Mn²⁺. The crystallite size to exciton bohr radius ratio being <1 indicates a strong quantum confinement effect in both CdS and ZnS QDs. The quantum confinement effect exists in the sequence of ZnS:Mn²⁺ < Zn_(1−x)Cd_xS:Mn²⁺ (x < 0.5) < ZnS < Zn_(1−x)Cd_xS < CdS < CdS:Mn²⁺.     

Fabrication of Co-doped ZnO nanorods for spintronic devices

Herein, single-crystalline Zn_1?xCo_xO (0.0≤x≤0.10) nanorods were prepared using a facile microwave irradiation method. Structural analyses by X-ray diffraction and transmission electron microscopy revealed the incorporation of Co²⁺ in the lattice position of Zn²⁺ ions into the ZnO matrix. Field emission scanning electron microscopy and TEM micrographs revealed that the length and diameter of the undoped ZnO nanorods were about ～2 μm and ～200 nm, respectively. For Co-doped ZnO, the length and diameter were found to increase with an increase of Co doping. The selected area electron diffraction pattern indicated that the Zn_1?xCo_xO (0.0≤x≤0.10) nanorods had a single phase nature with the preferential growth direction along the [0 0 1] plane. Raman scattering spectra confirmed the shift of the E ₂ ^high mode toward a lower wave number, suggested successful doping of Co ions at Zn site into the ZnO. Magnetic studies showed that Co doped ZnO nanorods exhibited room temperature ferromagnetism and the magnetization value increased with an increase in Co doping. The synthesis method presented here is a simple approach to prepare ZnO based diluted magnetic semiconductors nanostructures for practical application to spintronic devices.     

Studies on the magnetic, magnetostrictive and electrical properties of sol-gel synthesized Zn doped nickel ferrite

Zinc doped nickel ferrite i.e., Ni_1−xZn_xFe₂O₄ (0 ≤ x ≤ 0.6) have been prepared by using sol-gel method. X-ray diffraction of these samples shows the presence of single-phase cubic spinel structure. The room temperature magnetic measurements showed that saturation magnetization (M_s) increases with the substitution of Zn²⁺ ions up to x = 0.4 and thereafter it begins to decrease, whereas magnetostriction (λ) value decreases with the addition of Zn²⁺ in the Ni-Zn ferrite. Dielectric permittivity (?′), dielectric loss tangent (tan δ) and AC conductivity (σ_AC) for all the prepared samples have been studied as a function of frequency and composition in the range from 0.05 Hz to 10 MHz at room temperature. It has been observed that initially ?′, tan δ and σ_AC decreases with the substitution of Zn²⁺ up to x = 0.4 and then increases with the further addition of Zn²⁺ ions. Variation in the slope parameter s with zinc contents indicates the presence of different type of conduction mechanism in different compositions. The dielectric loss curves exhibit relaxation peaks which shift with the addition of Zn contents. The results have been explained on the basis of space charge polarization according to Maxwell-Wagner's two-layer model and the hopping of charges between Fe²⁺ and Fe³⁺ as well as between Ni³⁺ and Ni²⁺ ions at the octahedral sites.     

Morphology, optical and magnetic properties of Zn1−xNixO nanorod arrays fabricated by hydrothermal method

Zn_1−xNi_xO (x = 0, 0.05, and 0.1) nanorod arrays were prepared by hydrothermal method. Morphology and structure analysis indicate that the nanorods have single-crystalline wurtzite structure, and no metallic Ni or NiO phase exists. Room temperature ferromagnetism (RTFM) was observed in the Zn_0.9Ni_0.1O nanorods. In addtion, photoluminescence spectra of Zn_1−xNi_xO (x = 0, 0.05, 0.1 and 0.2) samples exhibit near band edge UV emissions and orange-red emissions. And the orange-red emission is confirmed to have originated from the interstitial oxygen defects.     

Structural, magnetic and electrical properties of Al substituted Ni-Zn ferrite nanoparticles

Nanocrystalline ferrite materials having the general formula Ni_0.7Zn_0.3Fe_2−xAl_xO₄ (0.0 ≤ x ≤ 0.5) have been synthesized by citrate-gel auto combustion method and characterized using X-ray diffraction (XRD), energy dispersive X-ray (EDX), field emission scanning electron microscopy (FE-SEM), dc magnetization, dielectric and impedance spectroscopy measurements. XRD studies confirm that all the samples show single phase cubic spinel structure. The crystallite size of Ni_0.7Zn_0.3Fe_2−xAl_xO₄ (0.0 ≤ x ≤ 0.5) nanoparticles calculated using the Debye-Scherrer formula was found in the range of 13-17 nm. The value of lattice parameter ‘a’ is found to decrease with increasing Al³⁺ content. EDX patterns confirm the compositional formation of the synthesized samples. FE-SEM micrographs show that all the samples have nano-crystalline behavior and particles show spherical shape. The variation of dielectric properties ?′,?″, and tan δ with frequency shows the dispersion behavior which is explained in the light of Maxwell-Wagner type of interfacial polarization in accordance with the Koop's phenomenological theory. The dc magnetization studies infer that magnetic moment of Ni_0.7Zn_0.3Fe_2−xAl_xO₄ (0.0 ≤ x ≤ 0.5) nanoparticles was found to decrease with Al doping. Impedance spectroscopy techniques have been used to investigate the effect of grain and grain boundary on the electrical properties of the synthesized compounds.     

A study of structural, optical and magnetic properties of Zn0.97−xCuxCr0.03O diluted magnetic semiconductors

A set of Zn_0.97−xCu_xCr_0.03O (0 ≤ x ≤ 0.03) samples has been synthesized by the sol-gel method. The structural, optical and magnetic properties of the samples were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and vibrating sample magnetometer (VSM). With Cu doping concentration increasing up to 2 at%, the XRD results showed that all diffraction peaks corresponded to wurtzite structure of ZnO, but for Zn_0.94Cu_0.03Cr_0.03O, the secondary phase of Cu emerged. PL measurements showed that Zn_0.97−xCu_xCr_0.03O powders and pure ZnO with the Cu concentration varied from 0.00 to 0.02 exhibited obvious blue shift; the green emission peak could be effectively enhanced with the increase of the Cu concentration. Magnetic measurements indicated that room-temperature ferromagnetism of Zn_0.97−xCu_xCr_0.03O was an intrinsic property when Cu concentration was less than 0.02. The saturation magnetization of Zn_0.97−xCu_xCr_0.03O (x = 0, 0.01, 0.02) increased with the increase of the Cu concentration.     

Multiwavelength excited novel red-emitting phosphor Eu-activated Li2Zn2(MoO4)3

Eu³⁺-activated Li₂Zn₂(MoO₄)₃ multiwavelength excited red-emitting phosphors were synthesized via a solid state reaction. The structure and photoluminescence characteristics were investigated by X-ray powder diffraction and fluorescent spectrophotometry, respectively. The excitation spectrum included a strong broadband ranging from 250 to 350 nm and some sharp peaks at 363, 384, 395, 465, and 533 nm, which matchs the radiations of near-UV or blue light-emitting diodes chip well. Upon excitation either of near-UV or blue even green light, the intense red emission with 615 nm peak can be observed, which is ascribed to the ⁵D₀-⁷F₂ transition of Eu³⁺ ions. The chromaticity coordinates (x = 0.65, y = 0.34) of the as-obtained phosphor is very close to the National Television Standard Committee standard values (x = 0.67, y = 0.33). All these characteristics suggest that Eu³⁺-doped Li₂Zn₂(MoO₄)₃ wavelength-conversion material to be suitable candidate red component for phosphor-converted white light-emitting diodes.     

Role of Cr ions on the microstructure development, and magnetic phase evolution of Ni0.7Zn0.3Fe2O4 ferrite nanoparticles

A series of ferrite samples with the chemical formula Ni_0.7Zn_0.3Cr_xFe_2−xO₄ (x = 0.0-0.5) were prepared by a sol-gel auto-combustion method and annealed at 600 °C for 4 h. The resultant powders were investigated by various techniques, including X-ray diffractometry (XRD), vibrating sample magnetometry (VSM), and permeability studies. The prepared samples have a cubic spinel structure with no impurity phase. As the Cr³⁺ content x increases, bulk density and crystallite size decrease, whereas porosity increases. The saturation magnetization decreases linearly from 58.31 to 42.90 emu/g with increasing Cr³⁺ content. However, coercivity increases with increasing Cr³⁺ substitution. The magnetic moments calculated from Neel's molecular-field model are in agreement in the experiment results. The initial permeability (μ_i) decreases with increasing Cr³⁺ substitution. The decrease in initial permeability (μ_i) is attributed to decrease in magnetization on addition of Cr³⁺. The real part of the permeability decreases gradually with increasing frequency in accordance with Snoek's law. The Curie temperature decreases linearly with increasing Cr³⁺ content.     

A novel photocatalyst and improvement of photocatalytic properties by Cu doping

A new series of photocatalysts, Bi₂Zn_2/3−xCu_xTa_4/3O₇ (Cu-β-BZT) crystals with pyrochlore structure were synthesized by the method of solid-state reaction (SSR). With small amount of Cu doped (0.01 ≤ x ≤ 0.04), the phase structure was kept to be monoclinic pyrochlore as pure β-BZT. The diffuse reflectance spectrum of Cu-β-BZT samples showed a red shift. The method of Cu doping enhanced the photocatalytic activity, and when the value of x is 0.03, the sample showed the highest activity, which is about 10 times higher than that of pure β-BZT under UV light. Especially, the samples of Cu-β-BZT showed photocatalytic activities under visible light irradiation (λ > 400 nm). Effects of the Cu doped on the photocatalytic activities of the catalysts were also discussed.     

Effect of chromium substitution on structural,electrical and magnetic properties of NiZn ferrites

Ni_0.5Zn_0.5Fe_2−xCr_xO₄ (0≤x≤0.5) ferrites were successfully prepared by conventional solid state reaction method to investigate the effect of chromium substitution on the structural, electrical and magnetic properties. X-ray powder diffraction results demonstrate that all the prepared samples are well crystallized single-phase spinel structures without secondary phase. As chromium concentration increases, the lattice parameter and crystallite size gradually decrease. The magnetic measurement indicates that saturation magnetization is substantially suppressed by Cr³⁺ doping, changing from 73.5 A·m²/kg at x=0 to 46.3 A·m²/kg at x=0.5. While the room-temperature electrical resistivity is more than four orders of magnitude enhanced by Cr³⁺ substitution, reaching up to 1.1×10⁸ Ω·cm at x=0.5. The dielectric constant monotonously decreases with rising frequency for these ferrites, showing a normal dielectric dispersion behavior. The compositional dependence of dielectric constant is inverse with that of electrical resistivity, which originates from the reduced Fe²⁺/Fe³⁺ electric dipole number by doping, indicating inherent correlation between polarization and conduction mechanism in ferrite.     

Phase evolution, crystal structure and dielectric behavior of (1 − x)Nd(Zn0.5Ti0.5)O3 + xBi(Zn0.5Ti0.5)O3 compound ceramics

The phase evolution, crystal structure and dielectric properties of (1 − x)Nd(Zn_0.5Ti_0.5)O₃ + xBi(Zn_0.5Ti_0.5)O₃ compound ceramics (0 ≤ x ≤ 1.0, abbreviated as (1 − x)NZT-xBZT hereafter) were investigated. A pure perovskite phase was formed in the composition range of 0 ≤ x ≤ 0.05. The B-site Zn²⁺/Ti⁴⁺ 1:1 long range ordering (LRO) structure was detected by both XRD and Raman spectra in x ≤ 0.05 samples. However, this LRO structure became gradually degraded with an increase in x. The dielectric behaviors of the compound ceramic at various frequencies were investigated and correlated to its chemical composition and crystal structure. A gradually compensated τ_f value was obtained in (1 − x)NZT-xBZT microwave dielectrics at x = 0.03, which was mainly due to the dilution of dielectric constant in terms of Claussius-Mossotti differential equation.     

The Enthalpies of Mixing of Liquid Ni-Sn-Zn Alloys

The partial and integral enthalpies of mixing of liquid ternary Ni-Sn-Zn alloys were determined. The system was investigated along two sections x _Ni/x _Sn ≈ 1:9, x _Ni/x _Sn ≈ 1:6 at 1073 K and along two sections x _Sn/x _Zn ≈ 9:1, x _Sn/x _Zn ≈ 4:1 at 873 K. The integral enthalpy of mixing at each temperature is described using the Redlich-Kister-Muggianu model for substitutional ternary solutions. In addition, the experimental results were compared with data calculated according to the Toop extrapolation model. The minimum integral enthalpy of approx. ?20000 J mol^-1 corresponds to the minimum in the constituent binary Ni-Sn system, the maximum of approx. 3000 J mol^-1 is equal to the maximum in the binary Sn-Zn system.     

Optical properties and magnetic properties of antisite-disordered Ni1–xCoxCr2O4 spinels

From the UV–Vis absorption spectra, the FT-IR absorption spectra and the Raman spectra, it is deduced that Co ions primarily occupy the tetrahedral (A) site, with a minor number of them entering into the octahedral (B) site in the Ni_1-xCo_xCr₂O₄ compounds. The origin of the position disorder of the Co ions is consistent with the similar ionic radii of the Co ion (0.65 Å) and the Cr ion (0.62 Å) at B site. The FT-IR peak at about 510 cm^?1 shifts towards high frequency side with the increasing cobalt content. It is resulted from the reduction of the cation–oxygen distance in the octahedron by the replacement of the Ni²⁺ with the Co²⁺ ions. The magnetic measurement shows that Curie temperatures (T_C) are 75 and 90 K for the compounds with x=0.2 and 0.8, respectively.     

Synthesis and study of nanocrystalline Ni-Cu-Zn ferrites prepared by oxalate based precursor method

Nanocrystalline ferrites of compositions Ni_0.5+1.5xCu_0.3Zn_0.2Fe_2−xO₄ (0 ≤ x ≤ 0.5) have been synthesized by using oxalate based precursor method at very low temperature. The Ni-Cu-Zn ferrite powder particles were obtained at 450 °C and they exhibit a crystallite size of 16-24 nm. The lattice constants were found nearly equal in all these samples due to minute difference in the ionic radius between Ni²⁺ and Fe³⁺ ions. The thermal analysis has showed the ferrite phase formation at very low temperature 377 °C. The two main spectroscopic bands corresponding to lattice vibrations were observed in the wavelength range from 300 to 1000 cm⁻¹. The IR bands at 570 cm⁻¹ (v₁) and 390 cm⁻¹ (v₂) were assigned to tetrahedral (A) and octahedral [B] groups. The spectroscopic bands shift with the increase of doping concentration. The magnetization was found to decrease with increasing doping concentration. The dielectric constant (?′) and dielectric loss tangent (tan δ) decreased with increase of frequency. The dielectric constant and dielectric loss obtained for the nanocrystalline ferrite samples appeared to be lower than that of the ferrites prepared by other synthesis techniques.     

Ni2+和Co2+复配（MoO2-4+Zn2+）对A20碳钢的缓蚀率研究

    用静态失重法研究了在标准配制水中Ni²⁺和Co²⁺复配（MoO^2-₄+Zn²⁺）对A20碳钢的缓蚀行为.结果表明,Langelier饱和指数（LSI）、MoO^2-₄浓度、Ni²⁺和Co²⁺浓度对缓蚀率的影响程度依次为：LSI>MoO^2-₄≈Co²⁺>LSI与MoO^2-₄的交互作用;Ni²⁺对提高缓蚀率几乎无贡献.     

Synthesis and conductivity of GdPO4 nanorods: Impacts of particle size and Ca doping

A series of Gd_1−xCa_xPO₄·nH₂O nanorods were prepared using a simple hydrothermal reaction which was optimized by tuning the pH values of the precursor. The resulted nanorods were characterized by X-ray diffraction, transmission electron microscopy, Fourier transformation infrared spectroscopy, and alternative current impedance technique. It is demonstrated that all Gd_1−xCa_xPO₄·nH₂O nanorods crystallized in a pure hexagonal structure. For x = 0, the particle dimension decreased with increasing the pH value. For x > 0, the solid solution limit of Ca²⁺ in GdPO₄·nH₂O nanorods was about 3 mol%, below which the lattice volume increased with increasing the doping level of Ca²⁺. The conductivities of nanorods were highly dependent on both the particle size and Ca²⁺ concentration, as indicated by the increased conductivity as particle size reduces or Ca²⁺ doping level increases. These observations were understood in terms of the dehydration and the introduction of HPO₄²⁻ defects by Ca²⁺ doping.     

Synthesis and characterization of MWCNTs/Co1−xZnxFe2O4 magnetic nanocomposites and their use in hydrogels

A novel magnetic nanocomposite of multiwalled carbon nanotubes (MWCNTs) decorated with Co_1−xZn_xFe₂O₄ nanocrystals was synthesized successfully by an effective solvothermal method. The as-prepared MWCNTs/Co_1−xZn_xFe₂O₄ magnetic nanocomposite was used for the functionalization of P/H hydrogels as a prototype of device to show the potential application of the nanocomposites. The nanocomposites were characterized by X-ray diffraction analysis, transmission electron microscopy and vibrating sample magnetometer. The results show that the saturation magnetization of the MWCNTs/Co_1−xZn_xFe₂O₄ magnetic nanocomposites increases with x when the Zn²⁺ content is less than 0.5, but decreases rapidly when the Zn²⁺ content is more than 0.5. The saturation magnetization as a function of Zn²⁺ substitution reaches a maximum value of 57.5 emu g⁻¹ for x = 0.5. The probable synthesis mechanism of these nanocomposites was described based on the experimental results.     

Magnetic properties and large magnetocaloric effect in Gd-Ni amorphous ribbons for magnetic refrigeration applications in intermediate temperature range

Amorphous Gd_68−xNi_32+x (x = −3, 0, 3) ribbons were prepared by melt-spinning method. The crystallization onset temperatures T_x1 for Gd_68−xNi_32+x amorphous ribbons with x = −3, 0, and 3 are 561, 568, and 562 K, respectively. All the samples undergo the second-order magnetic transition at temperatures between ∼122 (x = −3 and 3) and 124 K (x = 0). The Curie temperature T_C does not change with the composition significantly. The maximum isothermal magnetic entropy changes (−ΔS_M)_max of Gd₇₁Ni₂₉, Gd₆₈Ni₃₂, and Gd₆₅Ni₃₅ amorphous ribbons for a magnetic field change of 0-5 T were 9.0, 8.0, and 6.9 J kg⁻¹ K⁻¹, respectively. Large values of the refrigerant capacity (RC) were obtained in these ribbons. For example, Gd₇₁Ni₂₉ amorphous ribbon has a maximum RC value of 724 J kg⁻¹. Large magnetic entropy change and RC values together with high stability enable the Gd₇₁Ni₂₉ amorphous alloy a competitive candidate among the magnetic refrigeration materials working at temperatures near 120 K.     

A Study of the Origin of Weak Ferromagnetism in Zn1−x Co x O

To study the origin of ferromagnetism in Zn_1?x Co _x O thin films, its thermal diffusivity, in addition to its magnetization measurements, were analyzed. Thin films of Zn_1?x Co _x O (x = 0.03) were deposited on Si (100) substrates through ultrasonic spray pyrolysis. Magnetization M(B) measurements at low temperature showed a hysteresis loop that indicated the existence of ferromagnetic ordering in Zn_0.97Co_0.03O. However, the magnetic moment per Co ion was much lower than expected. A comparison of M(T) measured at zero-field-cooled and field-cooled conditions showed a superparamagnetic-like behavior, with a blocking temperature of about 130 K. Temperature dependence on the thermal diffusivity of Zn_0.97Co_0.03O showed a pronounced lambda-shaped minimum at 130 K, which indicated the existence of a second-order phase transition at this temperature. The weak ferromagnetism in the Zn_0.97Co_0.03O with the Curie temperature of 130 K was ascribed to the uncompensated magnetic moment at the surface of CoO nanoclusters.