Effect Of Co Substitution Research Articles

Neutron diffraction analysis and electrochemical performance of spinel Ni(Mn2−xCox)O4 as anode materials for lithium ion battery

The effects of Co substitution on the structure and electrochemical performances of spinel Ni(Mn2−xCox)O4 (x=0, 0.5, and 1.0) have been investigated. With the increase of Co content the lattice parameters decrease owing to the smaller ion radius of Co than Mn. The reversible capacity and cyclability of Ni(Mn2−xCox)O4 first increase and then decrease with the increase of Co content and NiMn1.5Co0.5O4 shows the best electrochemical performance in compared to the other two samples. Neutron diffraction and Rielveld refinement are further applied to analyze the site occupancies of the elements of Mn, Co, O and Ni. A certain amount of Co ions substitution are favorable to enhance the electrochemical performance, but excessive Co ions in 8a and 16d sites reduce the stability of host structure which leads to the poor electrochemical performance.

Controllable Eu valence for photoluminescence tuning in apatite-typed phosphors by the cation cosubstitution effect.

By cosubstituting [Ca(2+)-P(5+)] for [La(3+)-Si(4+)] in the Eu-doped Ca(2→8)La(8→2)(SiO4)6-x(PO4)xO2 (0 ≤ x ≤ 6) system, Eu(3+) ions are controllably and gradually transformed to Eu(2+). Thus, the emission colors consecutively changed from red to blue/green light. Furthermore, excellent warm-white lights with the low correlated color temperature (CCT) range of 3500-3800 K and a high color rendering index (Ra) (88.4-93.2) have been achieved by mixing the as-prepared phosphors at different cation cosubstitution ratios.

Effect of Co substitution for Mn on spin polarization and magnetic properties of ferrimagnetic Mn2VAl

Bulk (Mn1-xCox)2VAl (x = 0, 0.25, 0.50) alloys in highly ordered L21 structure with a very small amount of B2 disorder have been prepared and their magnetic properties have been measured. The value of saturation magnetizations of the alloys with x = 0, 0.25 and 0.50 are 1.88 μB, 0.84 μB and 0.07 μB, respectively, being consistent with 2.00 μB, 1.00 μB and 0 μB, respectively, predicted by the Slater–Pauling rule. This indicates that the stoichiometric MnCoVAl alloy is a fully compensated ferrimagnet (FCF). Spin polarization measurements using point contact Andreev reflection technique showed that the quaternary alloys exhibited higher intrinsic spin polarization than the parent ternary composition. The spin polarization of 0.60 deduced for the MnCoVAl alloy suggests that spin-polarized current can be extracted from FCF. Curie temperature (TC) and the effective anisotropy constant of (Mn1-xCox)2VAl alloys decrease with increase in Co content.

Spin-glass behavior in single crystals of hetero-metallic magnetic warwickites MgFeBO4, Mg0.5Co0.5FeBO4, and CoFeBO4

Magnetic properties of heterometallic warwickites MgFeBO4, Mg0.5Co0.5FeBO4, and CoFeBO4 are presented, highlighting the effect of Co substitution on the magnetic properties of these compounds. The analysis of magnetization and heat capacity data has shown that these compounds exhibit a spin-glass transition below TSG=10, 20 and 22K, respectively. Using zero field ac susceptibility as entanglement witness we find that the low dimensional magnetic behavior above TSG show quantum entanglement behavior χ(Τ)∝T−α(Τ) up to TE≈130K. The α parameters have been deduced as a function of temperature and Co content, indicating the existence of random singlet phase in this temperature region. Above TE the paramagnetism is interpreted in terms of non-entangled spins giving rise to Curie–Weiss paramagnetism. The different intra- and inter-ribbon exchange interaction pathways have been calculated within a simple indirect coupling model. It is determined that the triangular motifs in the warwickite structure, together with the competing interactions, induce frustration. The spin-glass character is explained in terms of the substitutional disorder of the Mg, Fe and Co atoms at the two available crystallographic sites, and the frustration induced by the competing interactions. The Co substitution induces uniaxial anisotropy, increases the absolute magnetization and increases the spin-glass freezing temperature. The entanglement behavior is supported in the intermediate phase irrespective of the introduction of anisotropy by the Co substitution.

Effect of co-substitutions (Ca–Mn) on structural, electrical and magnetic characteristics of bismuth ferrite

The polycrystalline samples of (Bi1−xCax)(Fe1−xMnx)O3 with x=0, 0.05, 0.10, and 0.15mol fraction were prepared by synthesizing through initial mixing of precursors by high-energy ball milling, and subsequent thermal treatment of the milled powders. Study of basic crystal parameters using x-ray diffraction technique of the calcined samples suggests that all the materials are crystallized in the distorted-perovskite (rhombohedral) structure which was supplemented and supported by their FTIR studies. The dielectric properties of the materials were investigated as a function of temperature and frequency and the temperature dependent dielectric constant and loss tangent of the modified system vary with substitution concentration (x) and frequency. Detailed studies of impedance exhibit that the electrical properties of the prepared systems are strongly dependent on temperature and frequency; and thus show a good correlation with their microstructures (i.e. bulk, grain boundary, etc.). Further, it is interesting to see the contributions of bulk, grain boundary and electrode in the impedance plots. The decrease in value of bulk resistance on increasing temperature suggests the existence of negative temperature co-efficient of resistance (NTCR) behavior in the materials. Room temperature M–H hysteresis measurements reveal that magnetization increases due to the structural distortion, and partial destruction of spin cycloid is caused by co-doping in BiFeO3 ceramics. Unlike magnetic response, the ferroelectric properties of the samples were found be enhanced on increasing mole fraction of x in BiFeO3.

Effect of Co substitution on hydrogenation and magnetic properties of NdMgNi4 alloy

The influence of Co substitution on the structural and magnetic properties of NdMgNi4−xCox (x⩽3) alloys and their hydrides has been investigated. The formation of NdMgCo4 compound has not been observed. The gas hydrogenation of these alloys resulted in the formation of NdMgNi4H4, NdMgNi3CoH4.8, NdMgNi2Co2H5.6 and NdMgNiCo3H6.2 hydrides. Transformation from cubic into orthorhombic structure upon hydrogenation has been confirmed for NdMgNi4H4 hydride, whereas it has been found that Co-containing hydrides preserved the parent cubic structure. PC diagrams at 50°C for NdMgNi4−xCox–H2 (x=0, 2, 3) showed only one absorption/desorption plateau, which equilibrium pressure decrease as the cell volume increase. The NdMgCu4 ternary compound has been synthesized, but it does not interact with hydrogen under normal conditions. Electrochemical investigations demonstrated that substitution of the nickel atoms by the cobalt ones in NdMgNi4 does not significantly influence on the maximum discharge capacity (244–261mAh/g) and all alloys are characterized by high cyclic stability. NdMgNi4 and its hydride display a Pauli paramagnet behavior. NdMgNi2Co2 displays a magnetic order below 50K whereas its hydride shows a Pauli paramagnet behavior similar to that of NdMgNi4H4.

Effects of Co-substitution on the structural and magnetic properties of NiCoxFe2−xO4 ferrite nanoparticles

The sol–gel auto-combustion method was used to prepare nanocrystalline powders of Co-substituted nickel ferrite with the general formula NiCoxFe2−xO4 (x=0.0, 0.1, 0.25, and 0.5). The effects of Co-doping on the structural, morphological, and magnetic properties of the samples were subsequently evaluated by X-ray diffraction (XRD), Fourier transform infrared (FTIR), field emission scanning electron microscopy (FE-SEM), and vibrating sample magnetometer (VSM). Using the MAUD program, the full pattern fitting of Rietveld method was employed to determine the exact coordinate of the atoms, unit cell dimensions, and ion occupancy. X-ray diffraction measurements by Rietveld refinement confirmed the crystalline structure and phase purity of all the ferrites prepared. FTIR results also confirmed the formation of a spinel phase and FE-SEM images showed that the particles were in the nanosize range. Moreover, Rietveld analysis and saturation magnetization (Ms) revealed that Co3+ replaced Fe3+ in the tetrahedral A-sites up to x=0.1. then, it replaced Fe3+ in both A- and B-sites for x≥0.25. Finally, VSM results demonstrated that while Ms remained nearly constant with increasing Co3+ substitution, coercivity (Hc) increased significantly. It may be suggested that the larger magneto-crystalline anisotropy of Co3+ ions is responsible for the increased Hc observed in the Co-doped Ni ferrite samples.

Effect of Co substitution on the magnetic and electron-transport properties of Mn2PtSn

The structural, magnetic and electron-transport properties of Mn2Pt1−xCoxSn(x = 0, 0.3, 0.5, 0.7, 1) ribbons prepared by arc-melting and melt-spinning were investigated. The rapidly quenched alloys with x = 0 and 0.3 were found to crystallize in the inverse tetragonal structure, but the structure transformed into inverse cubic as x increased to 0.5. At room temperature, the samples are ferro or ferrimagnetic, and the Curie temperature increases by 225 K from 370 K for Mn2PtSn (x = 0) to 595 K for Mn2CoSn (x = 1). The measured anisotropy constants for the inverse-tetragonal alloys are on the order of 1 Merg cm−3 at room temperature. The ribbons are moderately conducting with the room temperature resistivities being between 0.4 and 8.4 mΩ cm. Interestingly, the thermal coefficient of resistivity transforms from positive to negative and the magnetoresistance transforms from negative to positive as the value of x reaches 0.5.

The effect of Co substitution on the structural and magnetic properties of lithium ferrite synthesized by an autocombustion method

Nanoparticles of Li0.5−0.5xCoxFe2.5−0.5xO4 (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) were synthesized by the solution combustion method. The influence of Co substitution on the structural, morphological and magnetic properties of the prepared samples was studied. The XRD studies confirm the formation of single phase cubic spinel structure of the ferrite samples. Their lattice constants vary linearly from 8.31Å (x=0) to 8.35Å (x=0.6) with increasing Co2+ content, due to the ionic volume differences of Co2+, Fe3+ and Li1+ ions. Also, the bond lengths and site radii of octahedral and tetrahedral sites are found to increase linearly with Co2+ content. The crystallite sizes of all the prepared samples estimated from the full width half maximum (FWHM) of the strongest reflection of the planes (311) almost remain constant with the increase of Co2+ content. The surface morphology of the prepared ferrite samples show that some of the particles have a cubic and the others have a spherical shape. The average particle sizes of the samples obtained from SEM micrographs show an initial increase up to the sample of x=0.3 and then it decreases slightly. The magnetic properties of the samples have been studied by measuring M–H plots. Moreover, the saturation magnetization, remnant magnetization, and coercivity of the prepared samples increase up to the sample of x=0.3 (140.1emu/g, 49.4emu/g and 714.05Oe, respectively) and then they decrease again. The variation in the experimental magnetic moment μB exp with Co2+ content is explained on the basis of Neel's two sub-lattice model. Furthermore, the initial permeability of the prepared samples increases with increasing Co2+ content up to the sample of x=0.3 and then a slight decrease is observed again.

Effects of co-substitution on dielectric, magnetic properties and magnetoelectric coupling in nano CoFe2O4

In the present investigations few compositions of Co1−xZnxFe2−xLaxO4 (x=0.0, 0.1 and 0.3) nano particles of magnetic ferrite were synthesized by chemical co-precipitation method. The powder X-ray diffraction study reveals that the particle size decreases from 13nm to 11nm on account of co-substitution in cobalt ferrite. The co-substitution of Zn2+/La3+ into CoFe2O4 enhances dielectric response with low loss ~1.03 for Co0.7Zn0.3Fe1.7La0.3O4 for 10kHz at 300K. The temperature dependent dielectric and magnetic studies of Co0.7Zn0.3Fe1.7La0.3O4 reflect a coupling between dielectric and magnetic parameters near the magnetic transition temperature (Tc≈616K), which is responsible for the frequency dispersion of dielectric maxima. This provides the first evidence on the magnetoelectric coupling in CoFe2O4 system arising on account of Zn2+/La3+ co-substitution.

NFC의 자기 차폐용 Ni-Zn-Co 페라이트 자성체의 고주파 자기특성

【This study investigated the magnetic properties and frequency dispersion of complex permeability of Ni-Zn-Co ferrites used for magnetic shielding in near field communication (NFC) system. The sintered specimens of $(Ni_{0.7}Zn_{0.3})_{1-x}Co_xFe_2O_4$ composition were prepared by the conventional ceramic processing. The coercive force and saturation magnetization were measured by vibrating sample magnetometer. The complex permeability was measured by RF impedance analyzer in the range of 1 MHz~1.8 GHz. The coercive force increased and saturation magnetization decreased with increasing the Co substitution. The real and imaginary parts of complex permeability decreased and the resonance frequency increased with Co substitution, which was attributed to the increase in crystal anisotropy field and reduction in saturation magnetization. The effect of Co substitution could be found in reducing the magnetic loss to nearly zero at the operating frequency of NFC (13.56 MHz).】

Effect of Co substitution on magnetic ground state in Sm0.5Ca0.5MnO3

The effect of cobalt doping on the structural and magnetic properties of polycrystalline Sm0.5Ca0.5Mn1−xCoxO3 (0⩽x⩽0.20) has been studied. Powder X-ray diffraction (XRD), dc magnetization and ac susceptibility measurements have been performed. The orthorhombic deformation caused by the Jahn–Teller (JT) effect can be counterbalanced by Co3+ doping. Meanwhile, antiferromagnetic (AFM), spin glass (SG) and phase separation (PS) ferrimagnetic states appear, successively, with the increase of x. The critical slowing down model and the dynamic scaling equation were applied in some samples. The existence of two distinct length scales for SG and finite FM (ferromagnetic) order is the source of the progressive deviation which exists in the dynamic scaling fitting for x=0.05. Moreover, the small peaks at ∼8K in χ″(T) curves are believed to be induced by the canted moments of Mn ions as observed in Nd2/3Ca1/3MnO3.

Magnetic Phase Transition and Magnetocaloric Effect in Co-Doped Mn-Ni-Ge Melt-Spun Ribbons

The effects of Co substitution for Ni on Curie temperature TC, magnetic and magnetocaloric properties of Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.05</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.85-x</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ge (x = 0-0.85) alloy ribbons prepared by melt-spinning have been investigated by means of X-ray diffraction and magnetization measurements. All the as-spun Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.05</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.85-x</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ge (x = 0-0.85) ribbons crystallize in hexagonal Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> In-type structure at room temperature. The magnetic measurements at 100 K show that the as-spun ribbons exhibit good soft-magnetic behaviors with coercivity <;100 Oe. No martensitic magnetostructural transition can be observed in magnetization versus temperature M-T curves, whereas the Curie temperature T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> of the ferromagnetic to paramagnetic transitions of these ribbons increases from 205 K for x = 0 to 295 K for x = 0.85. The peak values of the maximal magnetic entropy changes (-ΔS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</sub> ) decrease from 6.0 to 3.4 J/kg K around T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> , under a field change of 0-50 kOe as x increases from 0 to 0.85, while the value of refrigeration capacity varies in the range of 170-250 J/kg.

Effect of Co Doping on Crystallographic and Optoelectronic Properties of ZnO Thin Films

In this study, Co-doped ZnO thin film was deposited by spray pyrolysis technique at 230 ∘C followed by annealing at 350 ∘C for 1 h. Crystal structure was investigated by X-ray diffraction method. All the samples showed polycrystalline hexagonal wurtzite structure. Variation of lattice parameters, volume of unit cell, and Zn–O bond length were investigated. The surface morphology of the films was studied by SEM measurements and wrinkled surface were observed for the Co-doped ZnO films. The optical characterization of the annealed samples was performed. The observed band gap values were found to decrease on Co doping in ZnO thin films. The effect of Co substitution on important optoelectronic properties, such as variation of the extinction and absorption coefficient, refractive index, and dielectric constant of the ZnO thin films were thoroughly investigated. It was found that Co doping has significant effect on these properties over a certain range of wavelength.

Spectroscopic investigation of an intrinsic room temperature ferromagnetism in Co doped ZnO nanoparticles

Pure and Co substituted ZnO nano crystalline particles were prepared by solution combustion technique using l-Valine as a fuel. As synthesized powder samples were characterized by X-ray diffractometer and SQUID magnetometer to confirm the formation of single phase wurtzite structure and to study the bulk magnetic response of the sample, respectively. Magnetic studies show that Co doped ZnO nanoparticles exhibit ferromagnetism (FM) at room temperature (RT). Furthermore, the electronic structure and element specific magnetic properties were investigated by near-edge X-ray absorption fine structure (NEXAFS) and X-ray magnetic circular dichroism (XMCD) measurements, respectively. The effect of Co substitution on the spectral features of Co–ZnO at O K-edge, Co L3,2 edge, Zn L3,2 edge have been investigated. The spectral features of NEXAFS at Co L3,2 edge is entirely different from the spectral features of metallic clusters and other impurity phases, which rules out the presence of impurity phases. The valence state of ‘Co’ ion is found to be in +2 state. The FM nature of the sample was confirmed through XMCD spectra, which is due to the incorporation of divalent ‘Co’ ions. Hence the presented results confirm the substitution of ‘Co’ ions at ‘Zn’ site in the host lattice, which is responsible for the RTFM.

Effect of co-substitution of La/Li on structure, microstructure, dielectric and piezoelectric behavior of Bi0.50Na0.50TiO3 ceramics

Polycrystalline specimens with compositions x = 0.04 and y ≤ 0.10 in (Bi1−xLax)0.5(Na1−yLiy)0.5TiO3 system are synthesized by semi-wet technique. Structure, microstructure, dielectric and piezoelectric properties are investigated in order to observe the effect of co-substitution of La/Li ions on A-sites of BNT ceramic system. Rietveld analysis of X-ray diffraction data for all the specimens reveals single phase formation with rhombohedral structure. Microstructures of these specimens indicate a decrease in grain size with homogeneous grain growth up to y ≤ 0.075 followed by anomalous grain growth for y = 0.100. The temperature dependence of dielectric plots exhibits a broad maximum whose position (Tm) is frequency dependent up to y ≤ 0.075. A switching from frequency dependent to frequency independent dielectric behaviour is observed with increasing Li concentration. All the samples show nearly saturated P–E loop at room temperature. The composition x/y = 0.04/0.025 exhibits improved ferroelectric with Pr = 29.26 µC/cm2 and piezoelectric constant of d33 = 70 pC/N.

Effect of Co substitution on magnetic properties of NinMn–Sn magnetic shape memory alloys

The effect of Co substitution on magnetic properties of NinMn–Sn shape memory alloy was revealed by first-principles calculations. Large magnetization difference in NinMn–Sn alloy obtained by addition of Co arises from enhancement of magnetization of austenite due to change of Mn-Mn interaction from anti-ferromagnetism to ferromagnetism. Total energy difference between paramagnetic and ferromagnetic austenite plays an important role in magnetic transition of Ni–Co–Mn–Sn. The altered Mn 3d states due to Co substitution give rise to difference in magnetic properties.

Effects of Co substitution for Fe on the glass forming ability and properties of Fe80P13C7 bulk metallic glasses

Bulk magnetic Fe80−xCoxP13C7 (x = 0, 5, 10, 15, 20 at.%) glassy alloy rods were prepared by the combination method of fluxing treatment and J-quenching technique, and the attainable maximum diameter for fully glass formation gets to 2.5 mm for x = 5. The effects of Co substitution for Fe on the glass formation ability (GFA), thermal stability, mechanical properties and magnetic properties have been investigated systematically. It was found that the partially substitution of Co for Fe can enhance the GFA of Fe80P13C7 alloy, while excessive substitution will lead to the degradation of GFA. The compressive test shows that the substitution of Co for Fe results in the decease of fracture strength, and then significantly enhance the room temperature plastic strain of the present Fe-based BMGs, which can be identified that the plastic strain at room temperature gets to 2.5% and 3.0% for x = 5 and 10, respectively. The saturation magnetization of Fe80−xCoxP13C7 (x = 0, 5, 10, 15, 20 at.%) BMGs firstly increases from 1.477 T to 1.550 T with increasing Co content from x = 0 to 5, and then deceases from 1.549 T to 1.519 T with increasing Co content from x = 5 to 20. The Curie temperature of the present FeCoPC BMGs quickly increases with the substitution of Co for Fe.

Leakage current under high electric fields and magnetic properties in Co and Mn co-substituted BiFeO3 polycrystalline films

Co and Mn co-substituted BiFeO3 films were prepared on Pt/Ti/SiO2/Si(100) substrates, and the effect of co-substitution on the structural, electric, and magnetic properties of the prepared films was systematically investigated. Cross-sectional transmission electron microscopy observations showed that the films were homogeneous; moreover, no magnetic secondary phases were observed in the films. Nano-beam energy-dispersive X-ray spectroscopy, carried out at various points in the films, revealed that Co and Mn were distributed in the films. Further, the average concentration of Bi, Co, Mn, and Fe was 59, 2, 2, and 37at.%, respectively; these values were almost consistent with the nominal composition of the precursor solution used. X-ray diffraction profiles of the films showed that the (012)-d-spacing decreased and (104) and (110) peaks merged into a single peak with increasing co-substitution content. The leakage current in films under high electric fields drastically decreased upon co-substitution without any degradation of ferroelectricity; moreover, this effect was also observed for single Mn-substituted materials. Saturation magnetization of the films monotonically increased with the co-substitution content, and this increase was quantitatively identical to that in the case of single Co-substituted materials. These results indicate that Co and Mn play significant roles in determining the properties of co-substituted BiFeO3 films.

Dopant mediated multiferroic behavior of HoMn1−xCoxO3 (x=0, 0.025, 0.05, 0.1)

Cobalt (Co) doped HoMnO3 (HMO) bulk ceramics having structural formula HoMn1−xCoxO3 (x=0, 0.025, 0.05, 0.1) are prepared using a conventional solid state reaction route and the effect of Co substitution at Mn site for the improvement of its structural, dielectric and multiferroic properties is studied. Optimizing the dopant concentration of Co (x=0.1), hexagonal phase (P63cm) of HMO is completely transformed to orthorhombic (Pbnm) structure. From magnetic measurement, it is observed that incorporation of Co atoms into HMO shows low temperature ferromagnetic behavior around 10K and its origin is attributed to the double exchange interaction between Mn3+- and Mn4+ ions. The materials also exhibit a sharp dielectric anomaly well above the room temperature around 530K at the concentration of x=0.1. Shifting of both magnetic transition as well as dielectric anomaly curve towards higher temperature is a clear indication for the existence of strong correlation between magnetic and electric dipole ordering. From XPS spectrum, it is found that oxidation state of Co atoms is +2 state and Mn atoms are both in +3 and +4 mixed state.