Effect Of Co Substitution Research Articles

Structural evolution and enhanced multiferroicity in BiFeO3-based ceramics via rare earth element co-substitution

In this study, multiple rare earth elements were introduced to modify the multiferroic properties of BiFeO3. The effects of co-substitution on the structural evolution and properties were thoroughly investigated. With increasing substitution content, the ceramics underwent a symmetry transition from R3c to Pna21 and finally to Pbnm. Co-substitution significantly enhanced the ferroelectric properties, with the highest remanent polarization of 33.14 μC/cm² observed at x = 0.10. Due to the symmetry evolution, ferromagnetism was released from the cycloidal spin structure, and the hysteresis loop gradually saturated, with the highest remanent magnetization (Mr) of 0.25emu/g observed at x = 0.16. The concurrent improvement in ferroelectricity and ferromagnetism resulted in substantial magnetoelectric coupling performance, with αME = 3.50mV/(cm·Oe). Moreover, direct current poling significantly induced the reverse transition from R3c to Pna21, indicating the potential for electrically controlled magnetism. This study provides a new perspective for modifying the magnetoelectric properties of BiFeO3.

Improved Electrochemical Performance of NASICON Type Na3V2-xCox(PO4)3/C (x = 0-0.15) Cathode for High Rate and Stable Sodium-Ion Batteries.

In recent years, the Na-ion SuperIonic CONductor (NASICON) based polyanionics are considered pertinent cathode materials in sodium-ion batteries due to their 3D open framework, which can accommodate a wide range of Na content and can offer high ionic conductivity with great structural stability. However, owing to the inferior electronic conductivity, these materials suffer from unappealing rate capability and cyclic stability for practical applications. Therefore, in this work we investigate the effect of Co substitution at the V site on the electrochemical performance and diffusion kinetics of Na3V2-xCox(PO4)3/C (x = 0-0.15) cathodes. All the samples are characterized through Rietveld refinement of the X-ray diffraction patterns, Raman spectroscopy, transmission electron microscopy, etc. We demonstrate improved electrochemical performance for the x = 0.05 electrode with a reversible capacity of 105 mAh g-1 at 0.1 C. Interestingly, the specific capacity of 80 mAh g-1 is achieved at 10 C with retention of about 92% after 500 cycles and 79.5% after 1500 cycles and having nearly 100% Coulombic efficiency. The extracted diffusion coefficient values through the galvanostatic intermittent titration technique and cyclic voltammetry are found to be in the range of 10-9 to 10-11 cm2 s-1. The post-mortem studies show excellent structural and morphological stability after testing for 500 cycles at 10 C. Our study reveals the role of optimal dopant of Co3+ ions at the V site in improving the cyclic stability at a high current rate.

Superconductivity of Co-Doped CaKFe4As4 Investigated via Point-Contact Spectroscopy and London Penetration Depth Measurements.

The iron-based superconductors (IBSs) of the recently discovered 1144 class, unlike many other IBSs, display superconductivity in their stoichiometric form and are intrinsically hole doped. The effects of chemical substitutions with electron donors are thus particularly interesting to investigate. Here, we study the effect of Co substitution in the Fe site of CaKFe4As4 single crystals on the critical temperature, on the energy gaps, and on the superfluid density by using transport, point-contact Andreev-reflection spectroscopy (PCARS), and London penetration depth measurements. The pristine compound (Tc≃36 K) shows two isotropic gaps whose amplitudes (Δ1 = 1.4-3.9 meV and Δ2 = 5.2-8.5 meV) are perfectly compatible with those reported in the literature. Upon Co doping (up to ≈7% Co), Tc decreases down to ≃20 K, the spin-vortex-crystal order appears, and the low-temperature superfluid density is gradually suppressed. PCARS and London penetration depth measurements perfectly agree in demonstrating that the nodeless multigap structure is robust upon Co doping, while the gap amplitudes decrease as a function of Tc in a linear way with almost constant values of the gap ratios 2Δi/kBTc.

Optimizing optoelectronic properties and energy harvesting potential of Co-doped LaFeO3: A DFT-based investigation

In response to the growing demand for advanced optoelectronic materials, this comprehensive investigation explores the effects of Co substitution on LaFeO3 using density functional theory. The study provides novel insights into the mechanical and optical properties of the doped structures. Structural stability is assessed through structural optimization, elastic stability tests, and enthalpy of formation calculations. The doped compounds exhibit significant improvements in electronic and optical properties, including enhanced thermal conductivity and reflectivity. Band structure analysis reveals metallic attributes and the Moss-Burstein effect, while magnetic property assessments indicate a decrease in magnetic moment due to Fe-Co degeneracy resulting from higher Co content. Mechanical analysis of elastic moduli B, G, and Y demonstrates enhanced durability and strength with metal-like conductivity, attributed to reduced anharmonicity. The study also highlights increased bond flexibility, suggesting potential applications in flexible electronics and UV light reflectors for effective shielding against photon radiation.

Electronic Band Structure and Fermi Surface Analysis of Ce2 Ni1-Xcoxge2: A Pseudo Potential Study

This study uses pseudopotential calculations to investigate the electronic band structure and Fermi surface properties of Ce2Ni1-xCoxGe2 alloys. The research problem centers on understanding the effects of Co substitution on the electronic properties of these alloys, particularly regarding potential high-temperature superconducting behavior. The methodology involves density of states (DOS) analysis and Fermi surface calculations for Ce2Ni1-xCoxGe2 alloys with varying Co concentrations. Results reveal a notable increase in DOS around the Fermi level with increasing Co substitution, indicative of enhanced metallic behavior and potential superconducting characteristics. Additionally, band structure analyses demonstrate the significant role of hybridization between Ce 4f, Ni/Co 3d, and Ge 4s/4p orbitals in determining electronic behavior. Fermi surface calculations unveil a transition from near-spherical to complex 2D and 3D shapes with higher Co concentrations, suggesting modifications in Fermi energy surface nestings or electron scattering. This study's conclusions emphasized the intricate electronic structure of Ce2Ni1-xCoxGe2 alloys and highlighted the potential for further exploration in high-temperature super conductivity research.

Effective incorporation of cobalt near surface region for cobalt-free cathodes in lithium-ion batteries

Cobalt-free cathode materials, particularly Ni-rich layered oxide cathode materials, are ideal for electric vehicle Li-ion batteries, offering high energy density and cost-effectiveness. However, high Ni content in high-temperature synthesis leads to issues like increased Li/Ni cation mixing and reduced rate capability, mainly due to the absence of Co. Therefore, this study investigated the utilization of a small amount of Co instead of completely removing it to enhance electrochemical performance. A simple pre-calcination process was used to induce Co substitution beneath the Ni-rich layered oxide cathode materials surface. A coating process was also performed for comparison. The Li/Ni cation mixing in the Co-substituted sample during high-temperature calcination was 2.43%, demonstrating a superior value compared to the Co-coating process. Rate capability tests showed superior performance for Co-substituted sample (164.2 mAh g−1) at 2 C compared to coated sample (151.0 mAh g−1). Moreover, Co substitution improved not only the cycle stability but also the high-temperature stability at an elevated state of charge.This study focuses on the surface modification of cobalt-free cathode, providing direct insight into the effects of Co substitution and typical Co coating and suggests an optimal process that uses small amounts of Co.

Dielectric performance of nanostructured magnesium oxide and effect of cobalt substitution

Here, we examined effect of Co substitution on dielectric characteristics of MgO nanostructures at various doping concentrations with the view to finding its use as a capacitor. The grain and grain boundary have significant impact on the dielectric characteristics' temperature and frequency dependency. Pure and Co doped MgO nanostructures showed dramatic drop in their dielectric constant and dielectric loss with increasing frequency. Reverse micelle micro emulsions of water-cyclohexane-CTAB ternary oil-surfactant-water systems were used to synthesize both pure and Co doped MgO nanostructures. Energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD), dynamic light scattering based particle size analysis (DLS-PSA), photoluminescence (PL), and Raman spectroscopy were used to analyze the synthesized materials. Different frequency and temperature range were studied for the complex permittivity of dielectric characteristics (ε * = ε'-jε") and the loss tangent (tanδ) and based on the experimental data, ε', ε", tanδ decreases as frequency and temperature increase.

The effect of co-substitution of heterovalent ions Ga3+and Sb5+on nonlinear optical properties of phosphate crystals

The nonlinear optical coefficient of the KTP crystal has been significantly improved after co doping with Ga3+and Sb5+ions (1.25 times that of the pure KTP crystal).

Effect of Co substitution on ferrimagnetic Heusler compound Mn3Ga

Effect of Co substitution on Mn3Ga is investigated using first-principles study for structural and magnetic properties. Without Co, ferrimagnetic Heusler compound Mn3Ga is in tetragonal phase. With Co substitution, depending on Co concentration (x), Mn3Ga prefers tetragonal (cubic) phase when x≤0.5 (x≥0.5). Ferrimagnetism is robust regardless of x in both phases. While magnetic moments of two Mn do not vary significantly with x, magnetic moments of Co in two phases exhibit different behaviors, leading to distinct features in absolute value of total magnetic moment (|Mtot|). When x≤0.5, in tetragonal phase, magnetic moment of Co is vanishingly small, resulting in a decrease of |Mtot| with x. In contrast, when x≥0.5, in cubic phase, magnetic moment of Co is roughly 1 μB, which is responsible for the increase of |Mtot|. Electronic structure is analyzed with partial density of states for various x. To elucidate the counterintuitively small Co moment, the magnetic exchange interaction is investigated, where exchange coefficient between Co and Mn(II) in x≤0.5 is much smaller than that in x≥0.5.

Effect of High-Anisotropic Co2+ Substitution for Ni2+ on the Structural, Magnetic, and Magnetostrictive Properties of NiFe2O4: Implications for Sensor Applications.

This work reports on the effect of substituting a low-anisotropic and low-magnetic cation (Ni2+, 2μB) by a high-anisotropic and high-magnetic cation (Co2+, 3μB) on the crystal structure, phase, microstructure, magnetic properties, and magnetostrictive properties of NiFe2O4 (NFO). Co-substituted NFO (Ni1-xCoxFe2O4, NCFO, 0 ≤ x ≤ 1) nanomaterials were synthesized using glycine-nitrate autocombustion followed by postsynthesis annealing at 1200 °C. The X-ray diffraction measurements coupled with Rietveld refinement analyses indicate the significant effect of Co-substitution for Ni, where the lattice constant (a) exhibits a functional dependence on composition (x). The a-value increases from 8.3268 to 8.3751 Å (±0.0002 Å) with increasing the "x" value from 0 to 1 in NCFO. The a-x functional dependence is derived from the ionic-size difference between Co2+ and Ni2+, which also induces grain agglomeration, as evidenced in electron microscopy imaging. The chemical bonding of NCFO, as probed by Raman spectroscopy, reveals that Co(x)-substitution induced a red shift of the T2g(2) and A1g(1) modes, and it is attributed to the changes in the metal-oxygen bond length in the octahedral and tetrahedral sites in NCFO. X-ray photoelectron spectroscopy confirms the presence of Co2+, Ni2+, and Fe3+ chemical states in addition to the cation distribution upon Co-substitution in NFO. Chemical homogeneity and uniform distribution of Co, Ni, Fe, and O are confirmed by EDS. The magnetic parameters, saturation magnetization (MS), remnant magnetization (Mr), coercivity (HC), and anisotropy constant (K1) increased with increasing Co-content "x" in NCFO. The magnetostriction (λ) also follows a similar behavior and almost linearly varies from -33 ppm (x = 0) to -227 ppm (x = 1), which is primarily due to the high magnetocrystalline anisotropy contribution from Co2+ ions at the octahedral sites. The magnetic and magnetostriction measurements and analyses indicate the potential of NCFO for torque sensor applications. Efforts to optimize materials for sensor applications indicate that, among all of the NCFO materials, Co-substitution with x = 0.5 demonstrates high strain sensitivity (-2.3 × 10-9 m/A), which is nearly 2.5 times higher than that obtained for their intrinsic counterparts, namely, NiFe2O4 (x = 0) and CoFe2O4 (x = 1).

Competition and Neutralization: Thermally Induced Crystallization and Phase Evolution of Amorphous Calcium Phosphate with Cosubstitution of Larger and Smaller Divalent Cations.

The presented study evaluated the effect of cosubstitution of larger and smaller divalent cations on the thermally induced crystallization of amorphous calcium phosphate (ACP). The predesigned combinations of larger (Sr2+ and Ba2+) and smaller (Mg2+, Cu2+, and Co2+) divalent cations were carried out and their effects on the thermodynamic equilibrium between α/β-tricalcium phosphate (TCP) were outlined. The coexistence of larger and smaller divalent cations shielded the formation of α-TCP and shifted the thermodynamic equilibrium toward the β-TCP, which implied that the smaller cations dominated the crystalline phase. However, the retarded crystallization induced by the larger cations still remained and allowed ACP to maintain its amorphous nature partly or completely until a higher temperature.

The enhanced of magnetic and electrical properties of Bi5FeTi3O15 compound with replacing Co for Ti sites

In this work, four-layered Aurivillius Bi5FeTi3-xCoxO15 (x = 0.0, 0.1, 0.3, 0.5, 0.6 and 0.7) compounds were fabricated by sol–gel method, in order to investigate the effect of Co substitution for Ti on the magnetic and electrical properties of Bi5FeTi3O15 (BFT). The phase formation and crystal structure of these compounds were investigated by using X-ray diffraction (XRD) and Rietveld refinement. The plate-like grain structure of particles were confirmed by field emission scanning electron microscope (FE-SEM). The mean thickness of Bi5FeTi3-xCoxO15 layers increase with increasing Co substitution. The multiferroic characterization of these samples were confirmed by the M−H and P-E hysteresis loops at room temperature. By substituting Ti sites by Co ion the magnetic behaviour of BFT changes from antiferromagnetic to ferromagnetic. The highest remanent magnetization value at room temperature is 0.67 emu/g that occurs in the cobalt substituted sample with x = 0.6. Simultaneously enhancing of magnetic and electrical properties in studied samples can allow us that use those for practical applications.

Integrated DFT and experimental study on Co3O4/CeO2 catalyst for direct synthesis of dimethyl carbonate from CO2

The oxygen deficient site on the catalyst has a strong impact on the activation of CO2 for the synthesis of dimethyl carbonate (DMC). The Co3O4/CeO2 catalyst exhibits multiple reduction behavior as cobalt metal species differ in the strength of their interaction with CeO2. This causes the surface reduction from Ce4+ to Ce3+ in solid solution Co-O-Ce. The dispersion of Co3O4 enhanced the formation of oxygen deficient site as revealed by XPS, CO2-chemisorption and TPR. The non-precious Co3O4/CeO2 nanorod was recognized as a potential catalyst for promoting Ce4+ to Ce3+ for CO2 activation and dimethyl carbonate synthesis (81.5% of yield). Energetics of oxygen vacancy formation of low index surfaces of CeO2 was determined with first-principles calculations based on DFT. Results disclosed the Ce4+ to Ce3+ formation energy of CeO2 due to Co substitution and corroborated the experimental results. Further, calculations provide the details of the effect of Co substitution on the electronic structure of reduced CeO2 surfaces. Estimated CO2 adsorption energy indicates (110) as the most active surface for activation of CO2.

Study on the effect of co-substitution of transition metals on O3-type Na-Mn-Ni-O cathode materials for promising sodium-ion batteries

BackgroundThe substitution of small quantity of electrochemically inactive and active elements described a propitious strategy for sodium-ion batteries (SIBs) to enrich the structural stability and electrochemical performance of O3-type cathodes. MethodsWe prepared the co-substitution of (Cu and Ti) O3-Na0.9Mn0.60Ni0.30Cu0.05Ti0.05O2 (MNCT), (Ti and Mg) O3-Na0.9Mn0.60Ni0.30Ti0.05Mg0.05O2 (MNTM), (Mg and Cu) O3-Na0.9Mn0.60Ni0.30Mg0.05Cu0.05O2 (MNMC), and bare O3-Na0.9Mn0.60Ni0.40O2 (MN) cathode materials by typical solid state reaction for SIBs. Significant findingsFrom Rietveld refinement, the MNCT, MNTM and MNMC cathode materials revealed a rhombohedral structure with the space group (R-3m), in which sodium ions occupied octahedral site. The MNCT, MNTM, MNMC and MN electrodes have discharge capacities of 184, 179, 174, and 218 mAh g−1 in a voltage range of 2–4 V at 0.1C rate, respectively. The bare MN system suffered the structural stability, it was rectified upon co-substituting with two different combinations using the partial amount of copper (Cu), titanium (Ti) and magnesium (Mg). The substitution in transition metal oxide (TMO2) layers enriched structural immovability of the O3-type cathode materials during electrochemical reaction for rechargeable SIBs.

Thermoelectric Properties of Co-Substituted Al-Pd-Re Icosahedral Quasicrystals.

The practical application of quasicrystals (QCs) as thermoelectric materials makes icosahedral (i-) Al–Pd–Re QC attractive because of its moderate electrical conductivity (~280 Ω−1 cm−1), relatively high Seebeck coefficient (~100 μV K−1), and low thermal conductivity (~1.3 W m−1 K−1) at room temperature. To develop a thermoelectric Π-shaped power generation module, we need both p- and n-type thermoelectric materials. In this work, we aimed to develop an n-type i-Al–Pd–Re-based QC and investigated the effect of Co substitution for Re on the thermoelectric properties, i.e., the electron-doping effect. We synthesized dense bulk samples with nominal compositions of Al71Pd20(Re1−xCox)9 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) via arc-melting, annealing, and sintering methods. We found that Co can produce n-type carriers in dilute substitution amounts of x = 0.1 and 0.2; however, the Seebeck coefficient at 300 K showed an n- to p-type transition with increasing x. This indicates that a simple rigid-band approximation is not applicable for i-Al–Pd–Re QC, which makes it difficult to synthesize an n-type i-Al–Pd–Re-based QC. Although the thermal conductivity was reduced from 1.28 (x = 0) to 1.08 W m−1 K−1 (x = 0.3) at 373 K by lowering of the electron thermal conductivity (electrical conductivity) and the alloying effect via Co substitution, the dimensionless figure of merit was not enhanced because of lowering of the power factor for all samples. The elastic moduli of i-Al–Pd–Re QC decreased by Co substitution, indicating that i-Al–Pd–Re-Co QC had a more ionic and brittle character.

Effect of Co-Substitution on Hydrogen Absorption and Desorption Reactions of YMgNi4-Based Alloys

Effect of Co-Substitution on Hydrogen Absorption and Desorption Reactions of YMgNi₄-Based Alloys

Effect of co-substitution of Na0.5Bi0.5TiO3 and CaTiO3 on the structure and properties of BiFeO3 ceramics

Effect of co-substitution of Na0.5Bi0.5TiO3 and CaTiO3 on the structure and properties of BiFeO3 ceramics

Sol-gel synthesis and characterization of praseodymium-doped and calcium-, titanium-substituted yttrium aluminium garnets Pr:Y3-xCaxAl5-yTiyO12

Mixed-metal garnets with novel chemical compositions (Pr:Y3-xCaxAl5-yTiyO12) have been synthesized by a simple aqueous sol–gel method. The praseodymium-doping and calcium- and titanium-substitution effects in these mixed-metal garnets have been investigated. The sol–gel derived garnet samples were characterized by powder X-ray diffraction analysis (XRD), FTIR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The positive effect of co-substitution with calcium and titanium ions in Y3-xCaxAl5-yTiyO12 samples in comparison with single aliovalent substitution of calcium in Y3-xCaxAl5O12 and titanium in Y3Al5-yTiyO12 samples was determined from the results of XRD analysis. The XRD patterns of these samples clearly showed that about 30 % of yttrium and aluminium could be substituted by calcium and titanium without destroying garnet crystal structure. On the other hand, the single-phase garnets Y3-xCaxAl5O12 and Y3Al5-yTiyO12 were obtained at lower substitutional level (∼20 % Ca2+ for Y3+ and ∼ 11 % Ti4+ for Al3+). Such different substitutional effects were explained by formation of different point defects in the crystal structures. The luminescent properties of Pr3+-doped Y3-xCaxAl5-yTiyO12 garnets were also investigated.

Effect of Cobalt Substitution on the Structural and Magnetic Properties of Bismuth Ferrite Powders

BiFeO3 (BFO) is a multiferroic material with excellent ferroelectric properties but with poor magnetic behavior. Therefore, we focused principally on the enhancement of the magnetic order of BFO. These multiferroic properties make BFO an excellent candidate for magnetoelectric devices at room temperature. Pure and Co-BiFeO3 powders were successfully synthesized via the sol–gel method at 700 °C. The effect of Co substitution on the corresponding structural and magnetic properties of BFO was studied. X-ray diffraction and Fourier Transform Infrared Spectroscopy measurements confirmed the rhombohedral perovskite structure in all samples. A secondary phase of CoFe2O4 (CFO) was detected for 9, 10, and 15% of Co doping. The scanning electron microscopy images of the Co-BFO particles showed a reduction in the particle size compared to the pure BFO powders. Vibrating sample magnetometry measurements evidenced the ferromagnetic hysteresis loop for the Co-BFO powders with values of saturation magnetization of 4.1 emu/g and a coercivity of 1083 Oe for 15% of Co doping. In this work, we report impurity free samples with notable magnetic properties at the same time, which is a difficult challenge in bismuth ferrite synthesis. This is the first step for later applications in future technology.

The effect of Co substitutions for Ni on microstructure, mechanical properties and corrosion resistance of Fe50Mn25Cr15Ni10 medium-entropy alloy

The microstructure, mechanical properties, and corrosion resistance of Fe50Mn25Cr15Ni10-xCox medium-entropy alloys (MEAs) with varying Co and Ni contents were investigated in this study. With increasing Co concentration, the microstructure of the MEAs changes from FCC single phase to FCC + HCP dual-phase. At room temperature, a rise in Co concentration increases the strength and ductility of the MEAs, while at liquid nitrogen temperature, the ductility, and the product of tensile strength and ductility of the MEAs decrease significantly. Furthermore, the corrosion resistance of the MEAs decreases significantly with increasing Co content. This work provides a research object for the further development of low-cost MEAs with excellent mechanical properties and corrosion resistance.