Role Of Co-doping Research Articles

Role of co-doping (Sm3+ and Nb5+) and Sintering Conditions on the Dielectric Properties of CaCu3Ti4O12 Ceramics

This research delves into the impact of Sm3+ and Nb5+ co–doping and the effect of sintering temperature on the grain size and the dielectric properties of CaCu3Ti4O12 (CCTO) ceramics synthesized via the sol–gel process. The Rietveld refinement provided detailed structural parameters, including atomic positions, bond lengths, bond angles, and R–factors, with a goodness of fit below 2% with no secondary phases. The expected core levels for Ca 2p, Sm 3d, Cu 2p, Ti 2p, Nb 3d, and O 1s were verified by XPS analysis, suggesting that these materials were present in their expected oxidation states. As the sintering temperature is increased, the average grain size grew from 0.61 ± 0.08 μm to 2.38 ± 0.32 μm. Notably, the sample sintered at 1050 °C exhibited huge dielectric permittivity (ε' ≈ 105) with good stability in the wide frequency range (102–105 Hz) with significantly low dielectric loss. The complex impedance analysis was studied to separate the contributions of grain and grain boundary resistances while the Nyquist plot revealed that the Rgb ranged from 4.26 × 103 to 4.95 × 106 Ω. The AC conductivities of all the ceramics displayed semiconducting characteristics, exhibiting a frequency dependence that conforms to Jonscher's power law. The observed performance of the dielectric of the ceramic can be ascribed to the Internal Barrier Layer Capacitance (IBLC) model.

Revealing effect of cobalt dopant on crystallography and optical characteristics of nanostructured cupric oxide

Cupric oxide is an interesting semiconducting material that has the potential to be applied in various technological utilizations. To understand the modified structure, the effects of Co doping at different concentrations (0, 1, 3, and 5 mol%) on the crystal structure, morphology, and optical properties of CuO nanoparticles synthesized by the co-precipitation method through heating at 400 °C for 2 h have been investigated. Synthesized samples were characterized by various techniques. X-ray diffractometer (XRD) results showed a monoclinic structure of CuO and impurity phase Co2O3 appearing when doping 5 mol% Cobalt. The crystallite size was found in the range of 25–48 nm. The crystallinity, texture coefficient, crystallite size, lattice constants, strain, and some physical properties (stress, Young's modulus, and strain energy) were calculated from the obtained XRD data. As a result, the lower Young's modulus and strain energy values of (111) crystal plane promoted the preferable growth in the direction. Fourier transform infrared spectrometer (FT-IR) was used to understand the chemical structure and confirm the substitution of Co in the samples. Scanning electron microscopy technique (SEM) was used to study morphology, appearing in the micron irregular flat plates that change to spherical particles when cobalt addition increases. Transmission electron microscope (TEM) micrographs show that structures of CuO are highly crystalline in nature and also provide clear evidence of spherical nanostructures in the Co-doped CuO. The Brunau–Emmet–Teller analysis method (BET) depicts a surface area improvement, showing 6.532 m2/g for the CuO and 19.285 m2/g for the 5 mol% Co-doped CuO sample. As more Co content, the decreasing energy bandgap of 2.75 to 2.58 eV was approximated using the Ultraviolet–Visible spectroscopy (UV–Vis) result. Photoluminescence spectra (PL) were found at about 440 and 470 nm, replied to oxygen vacancy (Vo) and copper vacancy (VCu), which are a sublevel affecting energy bandgap change. The role of Co dopant in improving the morphology and optical properties was discussed, associating with the structural characteristics and emerging intrinsic defects.

Investigation into the role of Co doping in the microstructure and magnetic characteristics of nanocrystalline Nd-Ce-La-Fe-B alloys

In this study, [Nd0.5(Ce0.5La0.5)0.5]17Fe78-xCoxB6 (x = 0 ∼ 1.5 at. %) ribbons are prepared via a direct melt-spun (wheel speed of 28 m/s). The impacts of Co doping on the crystal structure, Curie temperature Tc, magnetic parameters (Br, Hci and (BH)max) of [Nd0.5(Ce0.5La0.5)0.5]17Fe78-xCoxB6 alloys are systematically assessed. X-ray diffraction patterns and Rietveld refinement data demonstrate that the exclusive presence of a pure hard magnetic 2:14:1 phase without any secondary phases across all samples. Compared with Co-free sample (x = 0), the Br, Hci and (BH)max of Co-doped with x = 1 are increased by 15.0 %, 4.6 % and 42.9 %, respectively. The coercivity mechanism in the [Nd0.5(Ce0.5La0.5)0.5]17Fe78-xCoxB6 alloys arises from the integration of reversed domain nucleation and robust pinning of domain walls. The magnetic domain structure and quantitative analysis based on the microstructure and demagnetization behavior are conducted to investigate the exchange coupling interactions among the 2:14:1 grains. This exploration reveals that the enhanced magnetic properties stem from the refinement of the 2:14:1 phase's grains, leading to more uniform and smaller interaction domains.

Cobalt-doped MoS2 coated polyaniline composites as superior anode materials for high-performance lithium-ion batteries

Transition metal dichalcogenides represented by molybdenum disulfide (MoS2) have attracted worldwide attention due to their high specific capacity originating from the four-electron transfer reaction for lithium-ion batteries. Here, one nanoflower-like MoS2 with high specific surface area and more active sites is synthesized by a facile and effective hydrothermal method with cetyltrimethylammonium bromide (CTAB) as the surfactant. To improve the conductivity and structural stability of MoS2, Co doping and polyaniline (PANI) surface modification are carried out in sequence, and the obtained MoS2@Co/PANI hybrid materials show the improved electrochemical performance. In particular, the optimal hybrid material with 15 wt% PANI can exhibit a high discharge specific capacity of 1429.7 mAh·g−1 at 200 mA·g−1, and deliver a reversible capacity of 649.4 mAh·g−1 after 100 cycles. The excellent cycling and rate performances of MoS2@Co/PANI hybrid materials can be attributed to the enhanced conductivity resulting from the synthetic role of Co doping and PANI surface modification. One rational design is also offered to improve the electrochemical performance of functionalized electrode materials in lithium-ion batteries.

Highly porous Co-doped NiO nanorods: facile hydrothermal synthesis and electrocatalytic oxygen evolution properties.

Highly porous 3d transition metal oxide nanostructures are opening up the exciting area of oxygen evolution reaction (OER) catalysts in alkaline medium thanks to their good thermal and chemical stability, excellent physiochemical properties, high specific surface area and abundant nanopores. In this paper, highly porous Co-doped NiO nanorods were successfully synthesized by a simple hydrothermal method. The porous rod-like nanostructures were preserved with the added cobalt dopant ranging from 1 to 5 at% but were broken into aggregated nanoparticles at higher concentrations of additional cobalt. The catalytic activity of Co-doped NiO nanostructures for OER in an alkaline medium was assayed. The 5%Co-NiO sample showed a drastically enhanced activity. This result could originate from the combination of advantageous characteristics of highly porous NiO nanorods such as large surface area and high porosity as well as the important role of Co dopant that could provide more catalytic active sites, leading to an enhanced catalytic activity of the nanocatalyst.

Functionalized upconversion nanoparticles: New strategy towards FRET-based luminescence bio-sensing

• Current advancement in functionalized UCNPs for FRET-based bio-sensing. • Discussed impact of surface functionalization of UCNPs to enhanced the loading/detection limit. • Importance of UCNPs in optical bio-probe/detection. • Role of co-dopants is discussed to enhance the emission efficiency. • Future challenges and improvement of UCNPs based luminescent biosensing are proposed. Functionalized upconversion nanoparticles (UCNPs) have perceived massive success in the area of bio-photonic applications. UCNPs are extensively used as a successful emitter in terms of unique luminescent properties, minimum auto-fluorescence, high chemical &thermal photo-stability, deep tissue penetration, excellent biocompatibility, and low toxicity. The relatively high emission efficiency of the UCNPs creates them greatly attractive and encouraging materials for widespread usages in biomedical and clinical sciences. High color purity, easy surface functionalization, and good colloidal stability are the advantageous features of the UCNPs. Widespread efforts are dedicated to emerging operational approaches for the preparation and surface functionalization/engineering of luminescent UCNPs of varying morphologies, simplifying the advancement of this auspicious material for fluorescent resonance energy transfer (FRET) based luminescence biosensing applications. We widely review the recent advancement of UCNPs in optical bio-sensing applications, with importance on the synthesis, surface functionalization, emission efficiency enhancement factors, and their successful use in the detection of pathogenic diseases, free radicals, and biomarkers. A detailed overview of functionalization techniques for UCNPs has also been presented, with a special emphasis on organic ligands-functionalization, doping, and methods of biological species-encapsulation/conjugation. Based on the current scientific achievements, traditional optical applications such as bio-sensing, immunosensing, biomarkers are now added. Finally, as a roadmap scheme for study in this area, future trends and recent problems are emphasized.

Helping Thy Neighbor: How Cobalt Doping Alters the Electrocatalytic Properties of Hematite.

We present analysis of the indirect role of Co doping on the electrocatalytic activity of α-Fe2O3. Upon substitution of one of the Fe atoms in the hematite surface, we observed a promoting effect of the substitution, upon which the overpotential required for the water-splitting reaction decreased in all substitution sites investigated. The cobalt site itself, however, does not exhibit the improved properties with respect to the undoped hematite. The promoting effect results purely from the altering of the properties of the nearest Fe atoms in the hematite surface. We conclude that the overpotential is reduced upon formation of the structure resembling the O2 molecule strongly interacting with the surface between the Co and Fe sites, and this is consistent with the catalytic activity of the surface vacancies of the hematite.

Role of Co dopants on the structural, optical and magnetic properties of lead-free ferroelectric Na0.5Bi0.5TiO3 materials

Abstract Co-doped Na0.5Bi0.5TiO3 materials were fabricated by a sol-gel technique. The structural distortion of Co-doped Na0.5Bi0.5TiO3 materials was due to the difference between the radii of Co dopants and Ti hosts. The optical band gap decreased from 3.11 to 1.83 eV because of the local state of the Co cation in the band structure. Room temperature ferromagnetism emerged as compensation of diamagnetic background and possibly intrinsic ferromagnetic signals. The magnetic moment was determined to be ∼0.64 μB/Co at 5 K. The origin of the room temperature ferromagnetism in the Co-doped Na0.5Bi0.5TiO3 materials was also investigated through the first-principles calculation method. Our study provides physical insights into the complex magnetic nature of transition metal-doped ferroelectric perovskites and contributes to the integration of multifunctional materials into smart electronic devices.

Synthesis and role of co-dopants (alkaline earth divalents and halides) on the photoluminescence of Eu2+ doped BaAl2O4 phosphor

Synthesis and role of co-dopants (alkaline earth divalents and halides) on the photoluminescence of Eu2+ doped BaAl2O4 phosphor

Correlation effects in the ground state of Ni-(Co)-Mn-Sn Heusler compounds

AbstractWe present density functional theory calculations to study the interplay between magnetic and structural properties in Ni-Co-Mn-Sn. The relative stability of austenite (cubic) and martensite (tetragonal) phases depends critically on the magnetic interactions between Mn atoms. While the standard generalized gradient approximation (GGA) stabilizes the latter phase, correlation effects beyond GGA tend to suppress this effect. Mn atoms treated as magnetic impurities can explain our results, where a delicate balance between magnetic interactions mediated by Ni d and Sn p orbitals determines the equilibrium structure of the crystal. Finally, we discuss the role of Co doping in stabilizing ferromagnetic austenite phases.

Effect of Co-Dopant on the Phase Structure and Photoluminescence Properties of Sr2mgsi2O7: En2+ Phosphors

The role of co-dopants, i.e. Dy, Ce, Tb or Y in SMS : Eu, RE3+ phosphor sintered using solid state reaction method at 1250°C under forming gas was studied. All SMS phosphors exhibited tetragonal Sr2MgSi2O7 as the domain phase and monoclinic SrSiO3 as the minor phase based on XRD analysis. It is noted that only single blue emission (469nm) contributed by Eu2+ ions was detected in RTPL measurement regardless types of co-dopants introduced during the sintering process. This result indicates that the co-dopants did not act as luminance centres in the SMS phosphor. The time-decay PL and temperature dependent PL analysis suggest that Ce3+ ions acted as sensitizer which improved the luminescence intensity and afterglow property of SMS phosphor. The present of Dy3+ ions pro-longed the afterglow property by introducing more traps density in the SMS phosphor structure. The co-doping of Tb or Y into the SMS phosphor generated many non-radiative recombination centres which deteriorated the optical performance of SMS: Eu2+, RE3+ phosphor.

Role of Co doping on structural, morphological and magnetic properties of SILAR deposited magnetite (Fe3O4) thin films

Co doped Fe3O4 thin films were deposited by using Iron (II) Sulfate heptahydrate (FeSO4·7H2O) and cobalt sulfate heptahydrate (CoSO4·7H2O) as precursors using SILAR method. Structural analysis using XRD reveals a decrease in crystallite size with doping is due to the accommodation of dopant atoms into the host matrix and excess atoms occupy the interstitials. In accordance with this dislocation density is found to be increased with increasing doping concentration. XRD results also reveal that Co is substituted into the Fe lattice, since both Fe and Co have same ionic radii and hence the structural properties of the thin film are intact with minor internal modifications. Raman analysis was used to find the vibrations and the polymorphs of iron oxide and the doping. The morphology of the samples was studied using FESEM. Absorption and transmission spectra of the deposited thin films were analyzed using UV–Vis spectrometer, the absorption value decreases with increase in wavelength whereas, transmission value increases with increase in wavelength. The defects in the deposited films were studied using PL studies. Magnetic properties were analyzed using VSM and it confirms the exchange interactions between the dopant and host atoms.

The role of Co atoms in spin dependent electronic properties of graphite-like ZnO structures

A first principles study is employed to reveal the electronic properties of graphite-like Co doped ZnO structures composed of atomic layers when spin property of electrons is involved. The influence of Co atoms, which are substituting the Zn atoms, was addressed through distinct atomic arrangements formed by specific atomic configurations and various Co concentrations. We obtained that the spin dependent behavior is largely determined by the atomic arrangement which can crucially impact the electronic structure for a certain spin orientation. It was observed that atomic configuration is an essential factor which may reduce or enhance the minority-spin energy gap relative to majority one. It was shown that the emerging spin polarization can be manipulated by the atomic arrangement of the layered structures. Both the spin polarization and the magnetic moment were found to be contributed by both Co and O atoms. The stability of a system via formation energy, the role of Co dopants positioned at different Zn sites, the number of both Co atoms and layers in a supercell, and the mechanisms governing the spin dependent behavior of these structures are discussed. • Co dopants at distinct locations yield crucial changes in spin dependent behavior. • Spin dependent behavior is determined by atomic arrangement in Co doped ZnO systems. • Atomic configuration and Co concentration play a crucial role on minority band gap. • The magnetic moment is mostly contributed by Co-3d and O-2p orbitals.

Role of codoping on multiferroic properties at room temperature in BiFeO3 ceramic

Role of codoping (20% La in Bi-site and 10% Mn in Fe-site) on mutiferroic properties in insulating BiFeO3 ceramic have been investigated. The X-ray diffraction (XRD) with Rietveld refinement shows that the structure of Bi0.8La0.2FeO3 is orthorhombic (Pnma). Furthermore, it shows that on substitution of 10% Mn-ions in Fe-site, no structural change occurs which has been supported by micro-Raman study. DTA study shows that ferroelectric transition temperature (TC) decreases very fast due with La-doping and slowly with the Mn-doping. Measurement on magnetization vs. applied magnetic field (M–H) shows increase of magnetization due to codoping of La and Mn in BiFeO3. This may be due to partly destruction or suppression of the spin cycloid structure in it and/ or the introduction of the mixed valance state. P–E measurement shows high leakage in Bi0.8La0.2Fe0.9Mn0.1O3.

Role of Co doping on structural, optical and magnetic properties of TiO2

The paper deals with the influence of Co doping on the structural, optical and magnetic properties of TiO2. XRD and Raman measurements confirmed single phase anatase structure of the Co doped TiO2 without having any impurity phases. The results are explained in terms of the broadening of peaks and small shift of Raman scattering modes, which is caused by the generation of defects such as vacancies and interstitials and owe their presence due to the microscopic structural disorder of oxygen lattice. 10% Co doped TiO2 exhibits room temperature ferromagnetic behavior with a 0.937emu/g saturation magnetization and 65Oe coercivity. Optical spectra have red shift with increasing Co in TiO2, due to sp–d exchange interactions. These interactions may be responsible for the ferromagnetic properties of the samples and the carriers are spin-polarized to mediate the ferromagnetic ordering.

Coupled microstructural and magnetic transition in Co-doped Ni nano-arrays

A superparamagnetic (SM) to ferromagnetic (FM) phase transition was investigated in Co-doped (∼6%) electroless plated Ni arrays. The introduction of Co altered the microstructure of the Ni arrays from nanocrystalline to polycrystalline, resulting in a SM→FM transition. This Co-induced magnetic phase transition is similar to that observed after heat treatment of undoped samples [C. M. Liu, Y. C. Tseng, C. Chen, M. C. Hsu, T. Y. Chao, and Y. T. Cheng, Nanotechnology 20, 415703 (2009); C. C. Huang, C. C. Lo, Y. C. Tseng, C. M. Liu, and C. Chen, J. Appl. Phys. 109, 113905 (2011)]. The role of Co dopant was identified electronically using x-ray magnetic spectroscopy, revealing that the transition modified the Ni host’s electronic structure and enhanced its moment by effectively spin-polarizing the Ni 3d conduction band. This was distinctly different than in the heat treatment case, which underwent an electronically independent phase transition. The element-specific magnetic hysteresis of Co and Ni was also probed, which showed that the two elements were magnetically coupled.

Role of codopants in the luminescent output from Si:Er

A crystal-field model for the electronic structure of the Er3+ ion in silicon is presented. The parameters within the model are adjusted in order that the Stark energy splittings within the f shell reproduce the observed spectral features in a Si:Er sample that is codoped with nitrogen. The dominant crystal field possesses tetrahedral symmetry. Several additional spectral features are attributed to local mode vibrational sidebands. From this analysis, I conclude that the role of the codopants is to isolate the Er ion so that the relaxation energy does not go into the production of lattice phonons.