Effect Of Co Substitution Research Articles

Relationships between crystal structure and microwave dielectric properties of Li2(Mg1−xCox)3TiO6 (0 ≤ x ≤ 0.4) ceramics

Abstract Li 2 (Mg 1−x Co x ) 3 TiO 6 (x = 0, 0.1, 0.2, 0.3, 0.4) ceramics were prepared using the conventional solid-state reaction method. Effects of Co-substitution on the crystal structure, sintering characteristics, micro–structures, microwave dielectric properties and Raman spectra were investigated. Co-substitution would affect the crystal structure and further influence the microwave dielectric properties. On the basis of the chemical bond theory and Rietveld refinement, some intrinsic factors such as the lattice energy, bond ionicity were calculated to explain the variations of the microwave dielectric properties. Ti–O and Li–O bonds played major role in influencing intrinsic factors and correlations between intrinsic factors of Ti–O, and Li–O bonds and microwave dielectric properties were established. With the increase of x values, the dielectric constant ( e r ) gradually increased, which could be explained by the variations of the polarizability, bond ionicity of Ti–O bonds, and Raman vibration modes. The decrease of the quality factor ( Q·f ) could be predicted by the decrease of the bond valence, packing fraction and lattice energy of Ti–O bonds. The temperature coefficient of resonant frequency ( τ ƒ ) significantly correlated with the bond energy of Li–O bonds and thermal expansion coefficient of Ti–O bonds.

Effect of Co-substitution on the electrocatalytic properties of Ni1.5Fe1.5O4 for oxygen evolution in alkaline solutions

Some ternary ferrites having composition CoxNi1.5-xFe1.5O4 (0.0 ≤ x ≤ 1.25) have been synthesized by NH4OH co-precipitation method at 11.5 pH. Materials, so obtained, were tested for their electrocatalytic properties towards oxygen evolution reaction (OER) in the form film on Ni-support in alkaline solution. The study showed that the electrocatalytic properties the material increased with partial substitution of Co for Ni in the base oxide (Ni1.5Fe1.5O4). The value being highest with 0.5 mol Co-substitution. At E = 850 mV vs Hg/HgO in 1M KOH at 25 ºC, the electrode showed apparent current density 206.2 mA cm-2, which is about 3 times higher than the base oxide. The Tafel slope values were ranged between 46-82 mV decade-1. A pair of redox peak, an anodic (EPa = 522±28 mV) and corresponding cathodic (EPc= 356±9 mV), was observed in the cyclic voltammetry (CV) study of the material. The thermodynamic parameters namely, standard apparent electrochemical enthalpy of activation ( ), standard enthalpy of activation ( ) and standard entropy of activation ( ) for the oxygen evolution reaction (OER) have also been determined by recording anodic polarization curve in 1M KOH. The value of was observed to be almost similar with each oxide electrode. The values were highly negative and ranged between ~ -165 and ~ -207 J deg-1 mol-1. Phase and morphology of materials have been investigated by using physical techniques X-ray diffraction, infrared spectroscopy (IR) and scanning electron microscope (SEM), respectively.

RETRACTED: Effect of Co substitution on absorption properties of SrCoxFe12-xO19 hexagonal ferrites based nanocomposites in X-band

Abstract Cobalt doped M-type strontium hexaferrite nanoparticles (SrCo x Fe 12-x O 19 , x = 0.2–1.2) is synthesized and used as inclusions in Linear Low Density Polyethylene (LLDPE) matrix for developing nano-composites with 60 wt% of these nanoparticles. Absorption performance of the developed nano-composites is evaluated in the X-band. The thickness optimization is carried out for obtaining maximum reflection loss by using the transmission line model (TLM), with measured values of permittivity and permeability of the composite. The best reflection loss is observed experimentally for x = 0.8 with an absorber thickness of 3 mm for which a wide −10 dB bandwidth covering almost the entire X-band is obtained. The composites are light weight and not affected by exposure to water.

Effect of Co substitution on magnetic and magnetocaloric properties in multiferroic hexagonal YMnO3

Polycrystalline YMn1−x Co x O3 with x ranging from 0 to 0.1 was synthesized by solid-state reaction method. The magnetic and magnetocaloric properties were investigated by superconducting quantum interference design magnetometer. With the increasing of Co-doping, the YMn1−x Co x O3 shows complex magnetic properties, including the existence of ferromagnetic component and spin glass state. The Curie temperature and maximum magnetic entropy change are also strongly dependent on Co content. Those results were ascribed to the complex mixed valence characteristics of Mn ions originated from the Co-doping.

Influence of co-substitution driven property tailoring in lanthanum orthoferrites (LaFeO3)

Abstract In this paper, effect of partial co-substitution (La by Li at A-site and Fe by Mn at B-site) on structural, electrical, optical and magnetic properties of perovskite type LaFeO 3 is reported. Polycrystalline La 1−x Li x Fe 1−y Mn y O 3 (x = y = 0–0.2) has been prepared by modified Pechini route. X-ray diffraction (XRD) results confirmed single phase polycrystalline powder. Effect of co-substitution on structural property has been noted in terms of changes in Fe/Mn-O-Fe/Mn bond angle and lattice strain on Rietveld refinement. The co-substitution driven structural changes have also been corroborated by fourier transform infrared (FTIR) spectrum in terms of upward shift of Fe/Mn-O stretching mode and downward shift of Fe/Mn-O-Fe/Mn bending mode of vibrations. Surface morphology of the materials indicated typical nanocrystalline microstructure with visible change in grain size with change in substituent concentration. Structural changes on co-substitution has significant effect on magnetic property tailoring arising due to deviation in Fe/Mn-O-Fe/Mn bond angle and/or indirect exchange interactions between two magnetic sub lattices Fe/Mn via intervening oxygen ion. The dielectric spectrum exhibited typical non-Debye type response as confirmed by modulus spectrum which shows peak at specific frequency for all concentration accompanied by shift of peak position towards higher frequency side with increasing concentration. Estimated relaxation time and electrical conductivity shows thermally activated Arrhenius type response with a maximum conductivity ~ 5.37 × 10 −4 S cm −1 at 423 K for 20% co-substitution. This is attributed to combined effect of grain and grain boundary contribution.

Effect of cobalt doping in Nd1-xSrxMn1-yCoyO3

We investigate the effects of Co substitutions the associated magnetic phase changes and the orthorhombic lattice distortions in Nd0.6Sr0.4Mn1-xCoxO3. The effect of Co substitutions on the magnetic state and the orthorhombic lattice distortions has been studied. The orthorhombic distortion is found to be maximum (7.377 × 10-3) for the pure manganite phase and decreases almost linearly with Co doping, reaching its minimum value 1.044 × 10-3 1.044 × 10-3 for the pure cobaltites. Similar behavior has been found for unite cell volume. Since Co may have several oxidation states, it may also affect the (Mn4+/Mn3+) ratio, the double magnetic exchange interaction, the magnetic state and metal insulator transition.

Effect of Co substitution on the magnetic properties in Fe1−xCoxGa3

We investigated the effect of Co substitution in Fe1−xCoxGa3 by means of electric resistivity and magnetic measurements. Nearly ferromagnetic behaviors were observed in Fe1−xCoxGa3 system by the chemical substitution of Co for Fe in diamagnetic mother compound FeGa3, accompanying with a semiconducting to metallic transition. With the substitution of Co, the magnetization of Fe1−xCoxGa3 increases first, and then decreases and finally it becomes diamagnetic. The magnetic properties of Fe1−xCoxGa3 were analyzed in terms of self-consistent renormalization (SCR) theory and Takahashi’s theory. The spin-fluctuation parameters, fourth order expansion coefficients of magnetic free energy (), the magnetic susceptibility in the ground state X(0), the spectral widths of the spin fluctuation spectrum T0 and Ta in the frequency and wave-number spaces, respectively, were estimated from the parameters derived from magnetic measurements. The magnetic properties of Fe1−xCoxGa3 can be understood almost quantitatively by the SCR theory and Takahashi’s theory of spin fluctuations.

Effect of Co-substitution on microwave dielectric properties of Li3(Mg1−xCox)2NbO6 (0.00 ≤ x ≤ 0.10) ceramics

The Li3(Mg1−xCox)2NbO6 (0.00 ≤ x ≤ 0.10) ceramics were prepared by the solid-state reaction route in this paper. The effects of Co-substitution on phase composition, microstructure and microwave dielectric properties of the Li3Mg2NbO6 were investigated by a variety of characterization methods. XRD patterns and Raman spectrum revealed that the all the compositions possessed orthorhombic structure with the space group of Fddd. The Q·f values of samples sintered at 1300 °C increased from 91,600 GHz at x = 0 to 127,600 GHz at x = 0.02, which was basically attributed to the appropriate amount of Co2+. With the x value increasing from 0 to 0.10, the τf value was gradually shifted toward zero, which indicated that the ionic substitution could effectively adjust the crystal stability of the matrix. In addition, there were no significant changes in the dielectric constant and grain sizes in the Li3(Mg1−xCox)2NbO6 compositions. Out these compositions, the Li3(Mg0.98Co0.02)2NbO6 ceramic sintered at 1300 °C exhibited excellent microwave dielectric properties of ɛr = 15.22, Q×f = 127,600 GHz and τf = −3.64 ppm/°C, which made the ceramics promising for future applications.

Effect of Co substitution on the glass forming ability and magnetocaloric effect of Fe88Zr8B4 amorphous alloys

Effect of Co substitution on the glass forming ability and magnetocaloric effect of Fe88Zr8B4 amorphous alloys

Effects of Co substitution for Fe on the structural and magnetostrictive properties of melt-spun Tb0.2Nd0.8Fe1.9 ribbons

A series of Tb0.2Nd0.8(Fe1−xCox)1.9(0.0⩽x⩽0.4) Laves ribbons were prepared by arc-melting and subsequent melt-spinning technique. The effects of Co substitution for Fe on the structural and magnetostrictive properties of Tb0.2Nd0.8Fe1.9 ribbons were investigated. Tb0.2Nd0.8Fe1.9 ribbons consist of (Tb,Nd) Fe2 Laves phase and a minor of rare earth but free of (Tb,Nd) Fe3 phase. Almost single Laves ribbons can be obtained when x⩾0.1, which indicates that the Co substitution for Fe is beneficial for the formation of Laves ribbons. The lattice parameter of the Laves ribbons decreases with increasing x. The Curie temperature of the Laves phase and saturation magnetization of the ribbons both get maximum at x=0.2. Meanwhile, the magnetostriction Tb0.2Nd0.8Fe1.9 ribbons can be improved by a proper amount of substitution of Co for Fe.

Structural and magnetic properties of Co-substituted NiCu ferrite nanopowders

Co-substituted NiCu ferrite nanopowders with the chemical formula Ni0.5−xCu0.5−xCo2xFe2O4 (0≤x≤0.50) were synthesized by sol-gel auto-combustion method. The effects of Co substitution on the cation distribution, structural and magnetic properties of the NiCu ferrite nanopowders have been investigated. Differential thermal analysis-thermogravimetry (DTA-TG), X-ray diffraction (XRD), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM) measurements were used to characterize the chemical, structural and magnetic properties of the ferrite nanopowders, respectively. The DTA-TG results indicate that there are three steps of the combustion process. XRD results indicate that there are Fe2O3 and CuO impurity phases when x≤0.10. Furthermore, the lattice parameter increases, and the X-ray density and the average crystallite size decrease with increasing Co substitution. And the obtained particle size from TEM image is in very good agreement with the average crystallite size estimated by XRD measurements. The saturation magnetization and coercivity monotonically increase with the increase of Co substitution. The increase of the saturation magnetization is due to the substitution of Ni2+ and Cu2+ ions with lower magnetic moment by Co2+ ions with higher magnetic moment on the octahedral sites. And the increase of the coercivity is mainly due to the increase of magnetocrystalline anisotropy energy.

Ab initio study of effect of Co substitution on the magnetic properties of Ni and Pt-based Heusler alloys

Using density functional theory based calculations, we have carried out in-depth studies of effect of Co substitution on the magnetic properties of Ni and Pt-based shape memory alloys. We show the systematic variation of the total magnetic moment, as a function of Co doping. A detailed analysis of evolution of Heisenberg exchange coupling parameters as a function of Co doping has been presented here. The strength of RKKY type of exchange interaction is found to decay with the increase of Co doping. We calculate and show the trend, how the Curie temperature of the systems vary with the Co doping.

Effect of co-substitution on structural, optical, dielectric and magnetic behavior of LaFeO3

Effect of co-substitution by Na at La site and Mn at Fe site of perovskite type LaFeO3 on its structural, optical, dielectric and magnetic properties at room temperature have been studied. Single phase nanocrystalline La1−xNaxFe1−yMnyO3 (x = y = 0–0.2) have been prepared by modified Pechini route. Substantial effect of substitution on structural property has been observed, which is clearly visible in view of changes in Fe/MnOFe/Mn bond angle and lattice strain. The substitution concentration dependent structural changes have also been confirmed by Fourier transform infrared (FTIR) spectrum in terms of upward shift of stretching mode (Fe/MnO) and downward shift of bending mode of vibrations (Fe/MnOFe/Mn). Typical nanocrystalline surface morphology has been observed with visible change in grain size on changes in concentration, which is also confirmed by X-ray diffraction (XRD). These changes have profound effect on magnetic property tailoring and appear to be correlated with Fe/MnOFe/Mn bond angle deviation and indirect exchange interactions between Fe and Mn ions via intervening Oxygen ion. Dielectric response (εr ∼ 103) at room temperature was observed on Na and Mn co-substituted LaFeO3. The dielectric spectrum shows typical non Debye type behavior. Modulus spectrum reveals shift of peak position toward higher frequency side with increasing concentration i.e. concentration dependent relaxation time. Electrical conductivity shows thermally activated Arrhenius type response with a maximum of ∼2.5 × 10−4 S cm−1 at 450 K for La0.85Na0.15Fe0.85Mn0.15O3. Both grain and grain boundary contribution to conduction mechanism has been observed.

Co-substitution effect on the structural, electrical, and electrochemical properties of nanostructured CoxNi1-xMnP2O7 (x = 0, 0.25, 0.5, and 0.75)

Cobalt-nickel-manganese pyrophosphate nanostructures with formula CoxNi1-xMnP2O7 were prepared via the hydrothermal method at 150 °C, with further calcinations at 500 °C. A structural analysis of CoxNi1-xMnP2O7 samples was carried out using X-ray diffraction (XRD). The effect of Co substitution on the structural, electrical, and electrochemical properties of CoxNi1-xMnP2O7 is reported. The electrochemical results show that the specific capacity increases from 59 to 205 mAh/g with increasing Co content. This study demonstrates the Co substitution effect on the mixed electrical conductivity. The temperature dependence of the dc electrical conductivity, for both pure and Co2+-doped samples, obeys the Arrhenius law. The frequency dependence of ac conductivity for the materials exhibited a Jonscher’s universal power law. The plots of pre-exponent (n) versus temperature suggested that the conduction mechanism can be described using correlated barrier hopping model. The improved electrical conductivity and electrochemical proprieties of CoxNi1-xMnP2O7 nanomaterials could be ascribed to the synergistic effect of nickel and cobalt ions. The best results have been obtained for the composition x(Co) = 0.75, where the electrical conductivity is maximum, and the Co0.75Ni0.25MnP2O7 demonstrates the highest specific capacity, implying their promising potential applications in the energy storage.

The Effects of Co-Substitution and Al-Doping on the Structural Stability of LiNiO2

Developing advanced cathode materials that provide high specific energy and power is essential for the commercialization of Li-ion batteries for electric vehicles. The layered LiNi0.8Co0.15Al0.05O2 (NCA) has received attentions as a promising candidate due to its cheaper material cost than LiCoO2, competitive electrochemical performance, and improved structural stability than LiNiO2. Thorough understanding of the origin of structural instability of Ni-based cathodes and the mechanism of Co-substitution and Al-doping will enable further improvement of Ni-based cathodes and other types of cathode materials as well. In this talk, we present our computational work on the structural stability of NCA, with emphasis on the effect of magnetic ions. LiNi1-yCoyO2 (NC) was studied first. Atom-spin coupled cluster expansion (CE) based on the density functional theory (DFT) calculations was performed to find stable atom-spin configurations of NC. The cationic mixing was accounted for by assuming that each cationic lattice site can be occupied by any of Li, Co, or Ni. The result predicted three stable configurations at zero temperature: LiNi0.8Co0.2O2, LiNi0.67Co0.33O2, and LiNi0.5Co0.5O2, as well as several more configurations at finite temperature, especially at y < 1/3, which agreed to the experimental observation on the range of solid-solution phase NC. Interestingly, the configurations of solid-solution phase NC had Ni ions in Li-layer (Ni-defects). We also found that that the solid-solution phase NC became less dominant when the Co content increased, which suggested that Co substitution might have suppressed the formation of Ni-defects. DFT calculations with HSE06 functional were additionally performed to investigate the mechanism of Co substitution associated with the suppression of Ni-defects formation. The oxidation state of each ion was obtained by analyzing the magnetic moment and agreed well with experimental observations. We found that a Ni-defect tended to be Ni2+ by oxidizing one Ni ion in TM layer to Ni4+ when they formed the nearest neighbor pair. In this case, the antiferromagnetic spin distribution was possible for all pairs of paramagnetic Ni ions (Ni2+ and Ni3+), which implies the configurations with Ni-defects (Ni ions in Li layer) are thermodynamically more favorable than non-defective configurations where such the antiferromagnetic spin distribution is not possible due to magnetic frustration. When Co is substitued for Ni, the oxidation state of Co is Co3+, which is diamagnetic like Ni4+. Then the antiferromagnetic spin distribution for all paramagnetic ions is also possible even without creating Ni-defects and we will demonstrate that the most ideal case is when y=1/3. We performed further calculations to find stable NCA configurations by replacing a portion of Co in NC with Al. By comparing NC and NCA, the effect of Al-doping to the structural stability will be also discussed.

Unveiling the Role of Co in Improving the High-Rate Capability and Cycling Performance of Layered Na0.7Mn0.7Ni0.3-xCoxO2 Cathode Materials for Sodium-Ion Batteries.

Co substitution has been extensively used to improve the electrochemical performances of cathode materials for sodium-ion batteries (SIBs), but the role of Co has not been well understood. Herein, we have comprehensively investigated the effects of Co substitution for Ni on the structure and electrochemical performances of Na0.7Mn0.7Ni0.3-xCoxO2 (x = 0, 0.1, 0.3) as cathode materials for SIBs. In comparison with the Co-free sample, the high-rate capability and cycle performance have been greatly improved by the substitution of Co, and some new insights into the role of Co have been proposed for the first time. With the substitution of Co(3+) for Ni(2+) the lattice parameter a decreases; however, c increases, and the d-spacing of the sodium-ion diffusion layer has been enlarged, which enhances the diffusion coefficient of the sodium ion and the high-rate capability of cathode materials. In addition, Co substitution shortens the bond lengths of TM-O (TM = transition metal) and O-O due to the smaller size of Co(3+) than Ni(2+), which accounts for the decreased thickness and volume of the TMO6 octahedron. The contraction of TM-O and O-O bond lengths and the shrinkage of the TMO6 octahedron improve the structure stability and the cycle performance. Last but not least, the aliovalent substitution of Co(3+) for Ni(2+) can improve the electronic conductivity during the electrochemical reaction, which is also favorable to enhance the high-rate performance. This study not only unveils the role of Co in improving the high-rate capability and the cycle stability of layered Na0.7Mn0.7Ni0.3-xCoxO2 cathode materials but also offers some new insights into designing high performance cathode materials for SIBs.

Effect of bimetallic (Ni and Co) substitution on magnetic properties of MnFe2O4 nanoparticles

Nickel and cobalt substituted manganese ferrite nanoparticles (NPs) with the chemical composition NixCoxMn1–2xFe2O4 (0.0≤x≤0.5) NPs were synthesized by one-pot microwave combustion route. The effect of co-substitution (Ni, Co) on structural, morphological and magnetic properties of MnFe2O4 NPs was investigated using XRD, FT-IR, SEM, VSM and Mössbauer spectroscopic techniques. The cation distribution of all products were also calculated. Both XRD and FT-IR analyses confirmed the synthesis of single phase spinel cubic product for all the substitutions. Lattice constant decreases with the increase in concentration of both Co and Ni in the products. From 57Fe Mössbauer spectroscopy data, the variations in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values with Mn2+, Ni2+ and Co2+ substitution have been determined. While the Mössbauer spectra collected at room temperature for the all samples are composed of magnetic sextets, the superparamagnetic doublet is also formed for MnFe2O4 and Ni0.2Co0.2Mn0.6Fe2O4 NPs. The magnetization and Mössbauer measurements verify that MnFe2O4 and Ni0.2Co0.2Mn0.6Fe2O4 NPs have superparamagnetic character. The saturation and remanence magnetizations, magnetic moment and coercive field were determined for all the samples. Room temperature VSM measurements reveals saturation magnetization value close to the bulk one. It has been observed that the saturation magnetization and coercive field increase with respect to the Ni and Co concentrations.

Effect of Bi and Li co-substituted SrTiO3 ceramics on structural and dielectric properties

Polycrystalline Sr(1–x)(Bi, Li)xTiO3 ceramics (x = 0 and 0.02) are prepared by a microwave processing method. The effect of co-substitution on structural, dielectric properties and ac-conductivity were investigated. The XRD of ceramics shows single phase with cubic structure. The lattice parameter of the compounds is estimated from the XRD patterns which confirm the incorporation of Bi and Li in SrTiO3 ceramics. Studies revealed that the dielectric constant and dielectric loss increased with an increase of temperature and decreased with an increase in frequency. The maximum dielectric constant obtained at room temperature is around 570 and increased to around 104 at 600 °C measured at 1 kHz frequency whereas the maximum dielectric loss measured was 0.048 at 600 °C and the loss measured at room temperature is 0.02. The activation energy of the samples were investigated using Arrhenius plots.

Hydrogen storage properties of La1.8Ti0.2MgNi9–x Co x (x = 0, 0.1, 0.3, 0.5) alloys

La1.8Ti0.2MgNi9–xCox (x = 0, 0.1, 0.3, 0.5) alloys were prepared by magnetic levitation melting under argon atmosphere. The effects of Co substitution on the phase structure and the hydrogen storage properties of the alloys were investigated. The results show that LaNi5 and LaMg2Ni9 phases are contained in all experimental alloys. LaNi3 phase disappears and LaNi2 phase appears as x ≥ 0.1 and x ≥ 0.3, respectively. Electrochemical performances have been improved after Co substitution for Ni, for example, the discharge capacity and the high rate dischargeability (HRD) reach the maximum at x = 0.1, and the optimum cycling stability is obtained at x = 0.5. The positive impact of Co on the hydrogen diffusion rate in bulk enhances the HRD, but to high Co content (x ≥ 0.3), the unsatisfied hydrogen desorption capability brings relative low HRD compared with the alloy electrode at x = 0.1.

Effect of cobalt on structural, magnetic and magnetocaloric properties of La0.8Ba0.1Ca0.1Mn1-xCoxO3 (x = 0.00, 0.05 and 0.10) manganites

We have studied the effect of Co substitution on the structural, magnetic and magnetocaloric (MCE) properties of La0.8Ba0.1Ca0.1Mn1-xCoxO3 compounds with x = 0.00, 0.05 and 0.10. All samples were synthesized using polymerization complex sol-gel method. X-ray diffraction (XRD) studies show that all compositions crystallize in the rhombohedral structure with the R3¯c space group. Rietveld analysis indicates that each (Mn, Co)O6 octahedron has a little distortion and that the θ(Mn, Co)O(Mn, Co) bond angles decreases with increasing Co content. The zero field cooled (ZFC) and field cooled (FC) magnetizations reveal that all samples undergo a paramagnetic-ferromagnetic (PM-FM) phase transition and a large deviation is usually observed between ZFC and FC curves which is due to the presence of competing FM and antiferromagnetic (AFM) interactions leading to a glassy behavior. The Curie temperature (TC) is found to decrease from 282 K for x = 0.00–214 K for x = 0.10. Arrot’s plots reveal a second order nature of magnetic transition for all samples, which is also confirmed by landau’s theory and universal curves.