Substitution Of Co Atoms Research Articles

Ab Initio Study of Structural and Magnetic Properties of Cobalt Doped Zinc Oxide

Abstract.In this study, we have investigated the electronic and magnetic properties of Cobalt doped zinc oxide (ZnO) bulk materials using density functional theory (DFT) calculations. The substitution of Co atoms into the ZnO lattice is systematically explored to understand its impact on the electronic band structure, magnetic moments and stability of the material. It is observed that Co doping introduces localized magnetic moments of 3.073 μB associated with Co atoms. The electronic band structure exhibits the semi-metallic nature after the Co doping with a majority spin (↑) and a minority spin (↓) magnetic configuration hybridization between Co 3d and 2p orbitals of O, indicating the potential for spin-polarized transport in Co-doped ZnO. We have also analyzed the formation energies to assess the thermodynamic stability. It is observed that the binding energy per atom slightly decreased to -3.563 eV, indicating stable Co incorporation. From the obtained results it can be concluded that, through controlled doping strategies the electronic and magnetic properties in ZnO-based materials can be altered for desired properties.

The synergy of ferric surface anchoring and interior doping engineering enables anode with boosted potassium ion storage performances

Interfacial engineering, especially atomic substitution at the interface or inside the nanomaterials, is a promising strategy for fabricating high-performance electrode materials. Herein, an interfacial modification strategy was reported to develop cobaltous sulfide (CoS2) nanomaterials with Fe clusters modified on their interface and Fe single atoms partially substituted Co atoms in CoS2 (Fe-CFS), which were further wrapped by graphene networks, forming highly active Fe-CFS@graphene nanomaterials (Fe-CFS@C) with triple reaction interfaces. As the 1st interface, graphene can decrease their electrical resistance. At the 2nd interface, partial substitution of Co atoms in CoS2 by Fe single atoms can reduce its band gap and boost the potassium ion (K+) diffusion rate. At the 3rd interface, anchoring Fe clusters on the surface of CoS2 results in the formation of Schottky junction and promotes the formation of built-in electric fields, which accelerates the K+ insertion/extraction kinetics and depresses the dynamic polarization. Acting as anode for K+ battery, Fe-CFS@C exhibits a high reversible capacity of 755.8 mA h g−1 at 0.05 A g−1. Even at 10 A g−1, it can maintain 178.3 mA h g−1 over 4000 cycles due to the greatly enhanced electrochemical reaction kinetics and effectively improved structural stability.

КІНЕТИЧНІ ТА ЕНЕРГЕТИЧНІ ХАРАКТЕРИСТИКИ ТЕРМОМЕТРИЧНОГО МАТЕРІАЛУ TiCo1-xMnxSb: МОДЕЛЮВАННЯ ТА ЕКСПЕРИМЕНТ

The results of a complex study of the semiconductor thermometric material TiСo1-xMnxSb, х=0.01–0.10, for the producing of sensitive elements of thermoelectric and electro resistive sensors are presented. Microprobe analysis of the concentration of atoms on the surface of TiСo1-xMnxSb samples established their correspondence to the initial compositions of the charge, and X-ray phase analysis showed the absence of traces of extraneous phases on their diffractograms. The produced structural studies of the thermometric material TiСo1-xMnxSb allow to speak about the ordering of its crystal structure, and the substitution of Co atoms on Mn at the 4c position generate structural defects of acceptor nature. The obtained results testify to the homogeneity of the samples and their suitability for the study of electrokinetic performances and the manufacture of sensitive elements of thermocouples. Modeling of structural, electrokinetic and energetic performances of TiСo1-xMnxSb, х=0.01–0.10, for different variants of spatial arrangement of atoms is performed. To model energetic and kinetic performances, particularly the behavior of the Fermi level, the band gap, the density of states (DOS) distribution was calculated for an ordered variant of the structure in which Co atoms at position 4c are replaced by Mn atoms. Substitution of Co atoms (3d74s2) by Mn (3d54s2) generates structural defects of acceptor nature in the TiСo1-xMnxSb semiconductor (the Mn atom contains fewer 3d- electrons than Co). This, at the lowest concentrations of impurity atoms Mn, leads to the movement of the Fermi level from the conduction band to the depth of the band gap. In a semiconductor with the composition TiCo0.99Mn0.01Sb, the Fermi level is located in the middle of the band gap, indicating its maximum compensation when the concentrations of ionized acceptors and donors are close. At higher concentrations of impurity Mn atoms, the number of generated acceptors will exceed the concentration of donors, and the concentration of free holes will exceed the concentration of electrons. Under these conditions, the Fermi level approach, and then the level of the valence band TiСo1-xMnxSb cross: the dielectric-metal conductivity transition take place. The presence of a high-temperature activation region on the temperature dependence of the resistivity ln(ρ(1/T)) TiСo1‑xMnxSb at the lowest concentration of impurity atoms Mn, х=001, indicates the location of the Fermi level in the band gap of the semiconductor thermopower coefficient α(Т,х) at these temperatures specify its position - at a distance of ~ 6 meV from the level of the conduction band . In this case, electrons are the main carriers of current. The absence of a low-temperature activation region on this dependence indicates the absence of the jumping mechanism conductivity. Negative values of the thermopower coefficient α(Т,х) TiСo0,99Mn0,01Sb at all temperatures, when according to DOS calculations the concentrations of acceptors and donors are close, and the semiconductor is maximally compensated, can be explained by the higher concentration of uncontrolled donors. However, even at higher concentrations of impurity Mn atoms in TiСo0,98Mn0,02Sb, the sign of the thermopower coefficient α(Т,х) remains negative, but the value of resistivity ρ(х,Т) increases rapidly, and the Fermi level deepens into the forbidden zone at a distance of ~ 30 meV. The rapid increase in the values of the resistivity ρ(х,Т) in the region of concentrations х=0.01–0.02 shows that acceptors are generated in the TiСo1-xMnxSb semiconductor when Co atoms are replaced by Mn, which capture free electrons, reducing their concentration. However, negative values of the thermopower coefficient α(Т,х) are evidence that either the semiconductor has a significant concentration of donors, which is greater than the number of introduced acceptors (х=0.02), or the crystal simultaneously generates defects of acceptor and donor nature. The obtained result does not agree with the calculations of the electronic structure of the TiСo1-xMnxSb semiconductor. It is concluded that more complex structural changes occur in the semiconductor than the linear substitution of Co atoms by Mn, which simultaneously generate structural defects of acceptor and donor nature by different mechanisms, but the concentration of donors exceeds the concentration of generated acceptors. Based on a comprehensive study of the electronic structure, kinetic and energetic performances of the thermosensitive material TiСo1-xMnxSb, it is shown that the introduction of impurity Mn atoms into TiCoSb can simultaneously generate in the semiconductor an acceptor zone (substitution of Co atoms for Mn) and donor zones and of different nature. The ratio of the concentrations of ionized acceptors and donors generated in TiСo1-xMnxSb will determine the position of the Fermi level and the mechanisms of electrical conductivity. However, this issue requires additional research, in particular structural and modeling of the electronic structure of a semiconductor solid solution under different conditions of entry into the structure of impurity Mn atoms. The investigated solid solution TiСo1-xMnxSb is a promising thermometric material.

Energetic and electrokinetic characteristics of semiconducting solid solution TiСo1-xMnxSb

The samples of TiСo 1- x Mn x Sb solid solution ( x = 0.01, 0.02.03, 0.04, 0.05 0.07 and 0.10) were synthesized in an electric arc furnace. Homogenizing annealing was carried out at 1070 K for 720 hours. X-ray diffraction analysis was performed using the diffractometer DRON-2.0m (Fe K α -radiation). The temperature and concentration dependences of the electrical resistivity and thermopower relative to copper of the samples were measured in the temperature range 80–400 K. According to X-ray diffraction analysis, the synthesized samples belong to the MgAgAs structure type (space group F 3 m ). Previous researches of the half-Heusler phase TiCoSb and the solid solutions based on it TiCo 1- x Ni x Sb, TiCo 1- x Cu x Sb, Ti 1- x V x CoSb, Ti 1- x Mo x CoSb, Ti 1- x Sc x CoSb, allowed to establish both the defectivity in the structure of the TiCoSb compound and the mechanisms of the introduction of impurity atoms into its structure. It was found that in the structure of the compound TiCoSb there are simultaneously ~ 1% vacancies in the position 4a of Ti atoms and ~ 1% of additional Co * atoms in the tetrahedral voids of the structure, which can be described by the formula (Ті 0.99 Va с 0.01 )Co(Co * 0.01 )Sb. In this case, vacancies in the position of Ti atoms generate structural defects of acceptor nature, and additional Co* atoms in the tetrahedral voids of the structure generate defects of donor nature. The calculation of the density of electronic states of TiСo 1- x Mn x Sb solid solution, for an ordered variant of the structure in which the Co atoms are replaced by Mn atoms in 4 c position, showed that the Fermi level is in the band gap and shifts toward the valence band as the concentration of Mn increases. Such behavior of the Fermi level would have to lead to maximum values of resistivity and change the sign of the thermopower coefficient of TiСo 1- x Mn x Sb from negative to positive, and the intersection of the Fermi level and the valence band should change the conduction from semiconducting to metallic type. The obtained experimental results of the electrokinetic characteristics for TiСo 1- x Mn x Sb indicate that more complicated structural changes occur in the crystal than the linear substitution of Co atoms by Mn ones. At low concentrations of Mn atoms ( x = 0.01 and 0.02), the temperature dependence of resistivity has an activating character, at x = 0.03 and 0.04 it has metallic type and at concentrations x = 0.07 and 0.10 again activations take place. In turn, negative values of the thermopower coefficient of TiСo 1- x Mn x Sb for all investigated samples indicate that electrons are the majority charge carriers. Thus, based on the study of electronic structure, electrokinetic and energetic characteristics of TiСo 1- x Mn x Sb, it was established that both structural defects of acceptor and donor nature (the effective charge of which is opposite) are generated, the concentration of which increases with increasing Mn atoms. Keywords: electrical conductivity, thermopower coefficient, Fermi level, structural defect.

Molecular Dynamics Simulation of Structural and Transport Properties of Solid Solutions of Double Perovskites Based on PrBaCo2O5.5

The oxygen diffusion has been simulated by the molecular dynamics method in the solid solutions of PrBaCo2O5.5-based double perovskites: PrBa0.5Sr0.5Co2O5.5 with random substitution of half of Ba atoms by Sr atoms, PrBa0.5Sr0.5CoFeO5.5 with random substitution Ba → Sr and Co → Fe, PrBa0.5Sr0.5CoCuO5.5 with random substitution Ba → Sr and Co → Cu, and PrBa0.5Sr0.5CuFeO5.5 with random substitution Ba → Sr and random substitution of Co atoms by Fe and Cu atoms. It is shown that, varying the oxygen nonstoichiometry and/or chemical composition of solid solutions based on PrBa0.5Sr0.5Co2O5.5, one can significantly change the coefficient of thermal expansion of the materials. It is established for the first time that the maximum difference between the mobilities of oxygen atoms of different types observed in PrBa0.5Sr0.5Co2O5.5 significantly decreases at partial substitutions of cobalt by iron and copper. In the PrBa0.5Sr0.5CuFeO5.5 solid solution, the oxygen atom mobility in the (Cu,Fe)–O layers becomes somewhat higher than that in the Pr–O layers.

Cobalt substituted L10-MnAl thin films with large perpendicular magnetic anisotropy

The Co composition dependences of the structural and magnetic properties of L10-(MnAl)1−xCox alloy films were investigated. The lattice constants of (MnAl)1−xCox films gradually changed with increasing Co content while maintaining the L10-ordered structure below x = 0.08. The saturation magnetization gradually decreased with increasing Co content, and perpendicular magnetic anisotropy was observed below x = 0.08. In addition, Co substitution markedly improved the surface roughness of the films by decreasing the substrate temperature of (MnAl)1−xCox films. We found that both a high magnetic anisotropy and a small surface roughness can be obtained by the substitution of Co atoms into MnAl films.

The effect of Sn codoping on the local Co structural environments of (In0.95-xSnxCo0.05)2O3 thin films using x-ray absorption spectroscopy

The effect of Sn codoping on the local Co structural environments of the (In0.95-xSnxCo0.05)2O3 (x = 0, 0.02, 0.05, 0.08) films has been investigated in detail by x-ray absorption spectroscopy at Co K-edge and L-edge. The results show that the Sn codoping can remarkably influence the local Co structures of the films. For the films with low Sn concentration (x ≤ 0.02), most Co2+ atoms substitute for In3+ sites of In2O3 lattices, while a part of Co atoms form the precipitate of Co metal clusters. With further increasing Sn concentration (x > 0.02), the doped Co atoms are completely substitutionally incorporated into the In2O3 lattices. It can be concluded that the codoping of Co and Sn atoms forms p-n pairs of electronics and holes with opposite charge state, which can activate the substitution of Co atoms in In2O3 lattice and suppress the forming of metallic Co clusters. The p-n codoping method can provide a powerful guiding principle in designing the oxides based diluted magnetic semiconductors.

Effect of stoichiometry of Fe and Co on the temperature stability of the magnetic anisotropy in Pr-Dy-Fe-Co-B alloys

An increase in the cobalt concentration in Pr-Dy-Fe-Co-B alloys leads to the substitution of Co atoms for Fe atoms in the atomic positions, which are the nearest neighbors with the rare-earth metal atoms, and to the formation of a significant number of boron-rich phases. At the highest (limiting) cobalt concentrations, boron can be substituted for the transition metals. As a result, the exchange interaction between magnetic sublattices of the rare-earth and transition metals is weakened. In turn, this leads to a decrease in the contribution from the rare-earth ions to the magnetic anisotropy, the temperature stability of which increases.

Co doping effects on structural, electronic and magnetic properties in Mn2VGa

The electronic structure and magnetic properties of Co-doped Heusler alloys (Mn1−xCox)2 VGa (x=0.0, 0.25, 0.5, 0.75, 1.0) have been studied by first-principles calculations. The results show that the lattice constants decrease with increasing Co content except x=1.0. The spin polarization for x=0.5 is only 34%, much lower than the other concentrations. The compounds of x=0.0, 0.25 show nearly half-metallicity because the Fermi level slightly touches the valence bands. And the compounds of x=0.75, 1.0 exhibit the half-metallic character with 100% spin polarization. It is found the local moments of Mn(Co) basically show a linear increasing trend while the moments of V show a linear decreasing trend with increasing doping concentration. However, the local moments for x=0.5 quite depart from the linear trend. The majority-spin component at the Fermi level increases while the minority-spin component at the Fermi level decreases with the substitution of Co atoms for Mn atoms when x≤0.75. For x≥0.75, the majority-spin component remains more or less the same and the gap in the minority DOS increases with Co doping. The majority spin states are shifted to valence bands and the majority spin states around EF increase due to a leakage of charge from the unoccupied spin-up states to the occupied majority states with increasing Co content.

Structural and Mechanical Properties of RT<sub>2</sub>Zn<sub>20</sub> and RFe<sub>2-x</sub>Co<sub>x</sub>Zn<sub>20</sub>(R=Y, Sm; T=Fe, Ru, Os, Co, Rh and Ir)

The phase stability, crystal structure and mechanical properties of YT2Zn20 and SmT2Zn20 (T=Fe, Ru, Os, Co, Rh and Ir) compounds have been investigated by using interatomic potentials based on the lattice inversion technique. The calculated lattice constants are in good agreement with the experimental data. The lattice constants increase and Bulk modulus decrease as the transition metal T varies from 3d to 5d. The Y-based compounds with lower energies are more stable than the Sm analogs. Also, the Bulk modulus of YT2Zn20 series are larger than SmT2Zn20 series. Moreover, the mechanical properties of the quaternary compounds YFe2-xCoxZn20 and SmFe2-xCoxZn20­, such as the elastic constants and bulk modulus, have been calculated in this work. The substitution of Co atoms would decrease the cohesive energies and increase the bulk modulus of materials.

Pauli Paramagnetism of the Novel Uranium Intermediate Phase UCo<sub>3-x</sub>Ge<sub>x</sub> (0.2 ≤ x ≤ 0.4)

The new compound UCo3-xGex with x = 0.4 was prepared by direct solidification of the corresponding liquid phase, followed by annealing at 973 K. Single crystal X-ray diffraction carried out at room temperature showed that it crystallizes with the hexagonal space group P63/mmc (n°194) and the unit-cell parameters a = 4.890(5) Å and c = 16.405(5) Å. The substitution of Co atoms by germanium atoms in UCo3 (PuNi3 structure type) yields stabilization of the CeNi3 structure. The homogeneity range, evaluated by energy dispersive spectroscopy analysis, extends from x = 0.2(1) to 0.4(1). The electronic properties were investigated by means of DC magnetic susceptibility and DC electrical resistivity measurements. The phase is a Pauli paramagnet and exhibits electrical conductivity characteristic of strongly disordered metals.

Methane Oxidation at the Ni1-XCoX-Samaria-doped Ceria Cermet Anode

Substitution of Co atoms for Ni atoms in the Ni-based cermet anode resulted in a decrease in the anodic overvoltage and interfacial resistance between the anode and electrolyte. This effect has been confirmed for a samaria-doped ceria (SDC) electrolyte and a scandia-stabilized zirconia (ScSZ) electrolyte. The results of electrochemical measurements revealed that the enhancement of the direct oxidation of methane was caused by the modification of microstructure in the cermet anode.

Magnetic and Electronic Properties of the Compound Y(Co,Fe)<sub>5</sub> Calculated by the Augmented Spherical Wave Method

Energy band structure and density of states of the compound Y(Co,Fe)5 were obtained by the augmented spherical wave method. Also the localization of the magnetic moment inside the unit cell, the effect of pressure and the substitution of Co atoms by Fe atoms were studied at the temperature of 0 K. Metallic Co showed a magnetic moment of 1.5 B while metallic Y showed its non magnetic behavior. Inside the compound YCo5 the Y atom had a contribution of –0.3 B to the total magnetization of the unit cell. A negative pressure caused the change of the Fermi energy and the modification of the magnetic moment. With a big enough positive pressure the total magnetic moment dropped to zero. The substitution of Co by Fe caused a change in the compound from strong ferromagnetic to soft ferromagnetic.

Local structure study of Co-doped indium oxide and indium-tin oxide thin films using x-ray absorption spectroscopy

We have studied the local structural environment of Co in Co-doped indium oxide and indium-tin oxide films, obtained by magnetron sputtering. The $\text{Co}\text{ }K$-edge x-ray absorption spectroscopic studies have been correlated with the x-ray photoelectron spectroscopy, magnetic, and electrical transport measurements performed on the same films. Different contributions of oxidized $({\text{Co}}^{2+})$ and metallic $({\text{Co}}^{0})$ cobalt to the observed ferromagnetism in these films are found depending on the host semiconductor and Co content. Homogeneous substitution of Co atoms for the In sites is found in indium-tin oxide films with less than $7\text{ }\text{at}\text{.}\text{ }%$ of Co, obtained preferably by direct, not sequential, cosputtering. In indium oxide films with similar Co content, obtained by sequential deposition, substitution of Co for the In site is accompanied by a larger static local disorder. As the Co content increases, Co-metal clusters are formed.

Systematic investigation on structure and excitonic-related transitions: An evidence for Zn1−xCoxO alloy film as a wide gap semiconductor

Systematic investigations were performed concerning the crystal structure and excitonic-related transitions of Zn1−xCoxO layers. The substitution of Co atoms for Zn sites was initially identified from the intra-emissions originating from the 3d levels of the Co2+ ions. Microresonant Raman scattering (μ-RRS) revealed that the local crystal structure of the host was disordered even at Co concentrations of a few percent, as determined by monitoring the A1(LO) mode and also supported by the ω-rocking curves obtained from x-ray diffraction. A critical point (Γ-edge) derived from magnetic circular dichroism systematically shifted to higher energy with increasing x, representing clear evidence for a widening of the band gap, and that the photoluminescent peaks correlated closely with absorption peaks related to excitonic transitions. The obvious excitonic structures gradually became diffuse with the appearance of photoexcited charge-transfer levels of Co2+ ions when x exceeded 2%. This allowed for observations of excitonic luminescence of samples with a Co content not exceeding 0.8%. The excitonic luminescence for all Co-doped ZnO layers was superimposed distinctly with Stokes and anti-Stokes LO phonons. This was attributed to outgoing multiphonon resonance Raman scattering due to a Fröhlich interaction based on strong coupling between photoexcited carriers and LO phonons, and further supported by the results of μ-RRS.

Electrochemical Activity of Ni1-XCoX-Based Cermet Anode for Methane Oxidation

Partial substitution of Co atoms for Ni atoms in the Ni-based cermet anode resulted in a decrease in the anodic overvoltage and interfacial resistance between the anode and electrolyte. This effect has been confirmed for yttria-stabilized zirconia (YSZ) and scandia-stabilized zirconia (ScSZ) electrolytes. The Ni1-XCoX-ScSZ (-YSZ) cermet anode showed an increase in the cell performance with increasing amount of Co content up to approximately 0.5. The decrease in the anodic overvoltage and the interfacial resistance contributes to an enhancement of the cell performance. The results of electrochemical measurements and microstructural characterization revealed that the enhancement of the direct oxidation of methane is caused by the modification of microstructure due to a solid- solutioning effect in the starting NiO-CoO binary system.

First principles study on the electronic structure and effective exchange interaction of Y(Co1−xCux)5

In order to investigate the enhancement mechanism of coercivity of SmCo5 due to partial substitution of Co atoms by Cu atoms, we calculate, by the first principles band calculation, the magnetic parameters such as magnetic moments and exchange constants of Y(Co1−xCux)5 for 0≦x≦1. The moments and the Curie temperatures estimated from the exchange constants decrease almost linearly with the Cu concentration x and are in quantitative agreement with the measured values. It is proposed that the decrease of effective exchange interactions between R ions by the partial substitution of Co atoms by Cu atoms is responsible for the high coercivity of this system.

Magnetic state of intermetallic Ho 1− x Y x(Co 1.95Al 0.05) 2 compounds

In order to investigate the influence of Al atoms on the magnetic properties of the RCo 2 compounds, neutron diffraction, a.c. susceptibility, thermal expansion and electrical resistivity measurements have been performed on the Ho 1− x Y x (Co 0.95Al 0.05) 2 compounds. A comparison of this system with the Ho 1− x Y x Co 2 compounds with x > x c = 0.58 shows that the substitution of Co atoms by Al atoms decreases the critical field which produces the splitting of the d-band. This leads to a long-range ferrimagnetic order in Ho 1− x Y x (Co 0.95Al 0.5) 2 with 0.58< x<0.8, while in the Ho 1− x Y x Co 2 compounds the Ho subsystem shows a short-range order and the Co subsystem remains paramagnetic.

A study of structure order of R(CoCu)5 compounds

We made use of neutron diffraction to study the crystal structure of R(Co1−xCux)5, in which x = 0.0, 0.2, 0.4, and 0.6, R = Y and Ce. From the analysis of neutron diffraction spectra, we found the Cu atoms prefer to occupy the 2c site. Meanwhile, we studied the thermal expansion behavior of CeCo5 and Ce(CoCu)5 compounds by high temperature x-ray. It showed an invar-type thermal expansion anomaly in the axis c below the Curie temperature. The anomalies are considerably reduced on the partial substitution of the Co atoms by the Cu atoms. All of these characteristics can be explained with the order of the substitution of Co atoms by Cu atoms.

Investigation of preferred substitution of Co atoms in Fe-Si-Al sendust type alloys

Investigation of preferred substitution of Co atoms in Fe-Si-Al sendust type alloys