Substitution Of Cu For Co Research Articles

Effect of Cu substitution on the type of magnetic phase transition and magnetocaloric effect in the ErCo2-xCux compounds

In this paper, the crystal structure, magnetic phase transition and magnetocaloric properties of the ErCo2-xCux (x = 0.12, 0.24, 0.36 and 0.48) compounds have been investigated in detail. All of the compounds crystallize in the C15 cubic Laves structure (MgCu2-type) with the Fd-3 m space group. The substitution of Cu for Co is accompanied by an increase of the Curie temperature Tc from 31.5 K to 68 K for x varying from 0.12 to 0.48. The nature of the magnetic phase transition, determined by the results of the Arrott plots and Landau theory, changed from a first order to a second order in the ErCo2-xCux compounds with the Cu content increasing. The isothermal entropy change -∆SM is calculated according to isothermal magnetization measurements using Maxwell’s relation. For an applied magnetic field change of 0–5 T, the -∆SM decreased from 30 J kg−1 K−1 for x = 0.12 to 10.9 J kg−1 K−1 for x = 0.48, whereas the working temperature range became wider due to that the magnetic transition type changed from a first order to a second order, which is a benefit for the application of the magnetic refrigeration. The corresponding refrigerant capacity RC values are 270.8 J kg−1, 194.1 J kg−1, 261.8 J kg−1 and 264.8 J kg−1, respectively.

Effects of partial substitution of Cu for Co on the microstructure and properties of WC-Co-Mo cemented carbides

In this work, Co–Cu metals were used as binder phase of cemented carbides. The influence of Cu content (0.8, 1.2, 1.6, and 2.0 wt%) on microstructure and properties of WC-Co-Cu-Mo alloys was discussed compared with WC-Co and WC-Co-Mo alloys. The results showed that the relative density, hardness, and transverse rupture strength of WC-Co alloys were significantly improved, and the WC average size, wear rate and corrosion resistance were greatly decreased by adding 1.2 wt% Cu. Among them, the hardness and density of WC-Co alloy increased from 1713 HV30 and 98.83% to 1908 HV30 and 99.31%, respectively. The average WC grain size and the corrosion rate of WC-Co alloy under HCl solution decreased from 0.68 μm and 303.23 μA cm−2 to 0.53 μm and 27.32 μA cm−2, respectively. These phenomena indicated that the doping of proper Cu into WC-Co-Mo alloys could enhance the comprehensive performance of WC-Co alloy.

A new strategy for remarkably improving anti-disproportionation performance and cycling stabilities of ZrCo-based hydrogen isotope storage alloys by Cu substitution and controlling cutoff desorption pressure

ZrCo1-xCux (x = 0–0.3) alloys for hydrogen isotope storage were prepared via induction levitation melting. The effects of partial substitution of Cu for Co on the microstructure, hydrogen storage properties including hydriding-dehydriding kinetics, thermodynamic characteristics, cycling stability and related mechanism have been systematically investigated. It is found that all synthesized alloy ingots consist of ZrCo main phase, the grain size is further refined but the segregation of Cu element at grain boundary is more serious with the increase of Cu content. The pressure-composition isotherms for dehydrogenation show that both ZrCoH3 and ZrCo0.9Cu0.1H3 hydrides undergo one-step desorption, while ZrCo0.8Cu0.2H3 and ZrCo0.7Cu0.3H3 hydrides experience two-step desorption since a new middle hydride phase of ZrCoH0.8 with CrB-type orthorhombic structure is discovered during their dehydrogenation. This result is proposed to be linked with the changed electronic structure and lattice distortion induced by Cu substitution. To compare their dehydriding kinetics, the apparent activation energies for hydrogen desorption of different hydride phases in the alloys are also calculated systematically, and the value of Ea for hydrogen desorption of ZrCoH3 phase is decreased from 118.02 kJ/mol to 95.90 kJ/mol, 77.98 kJ/mol and 78.65 kJ/mol, respectively. Prominent cycling stabilities of the Cu-substituted alloys are obtained and follow the trend: ZrCo0.8Cu0.2 > ZrCo0.7Cu0.3 > ZrCo0.9Cu0.1 > ZrCo. Specifically, the optimum cycling stable capacity of ZrCo-based alloy is increased from 0.4 wt % to 1.21 wt %. Furthermore, the ZrCo0.8Cu0.2 alloy exhibits further enhanced cycling stability during the cycle by controlling cutoff desorption pressure at 0.253 bar, where only the first-step dehydrogenation happens. Therefore, a new strategy for improving anti-disproportionation performance of ZrCo-based alloys by controlling cutoff desorption pressure is also proposed, which is in favor of the enhanced cycling stability and further application of Cu-substituted ZrCo-based alloys for hydrogen isotope storage and delivery in the International Thermonuclear Experimental Reactor (ITER).

Non-isothermal crystallization kinetics and fragility of Zr56Co28Al16 and Zr56Co22Cu6Al16 bulk metallic glasses

The role of substitution of Cu for Co on the non-isothermal crystallization kinetics and fragility of Zr56Co28Al16 and Zr56Co22Cu6Al16 bulk metallic glasses (BMGs) were evaluated by differential scanning calorimetry (DSC). The X-ray diffraction, transmission electron microscopy and microhardness test were used to investigate the glassy alloys structure. DSC results exhibited two crystallization processes for both BMGs. All the characteristic temperatures except glass transition temperature of parent alloy were more sensitive to heating rate than those of Cu containing alloy. The activation energies of characteristic temperatures were obtained by Kissinger and Ozawa methods. The results showed that the activation energy of glass transition decreased and the other activation energies increased with Cu addition. Also, the local Avrami exponents at various heating rates were calculated by the Johnson–Mehl–Avrami equation. The n value variations for each crystallization process were in almost similar trends for both BMGs. The results demonstrated that the transformation kinetics is dominated by diffusion-controlled three-dimensional growth with increasing nucleation rate for the first crystallization process and also for initially stage of the second crystallization process. However, the crystallization is dominated by interface-controlled three-dimensional growth with increasing nucleation rate at final stage of the second crystallization processes. In addition, both BMGs were classified into “strong glasses”, depending on the calculated values of fragility index.

Magnetic and electronic properties of the Cu-substituted Weyl semimetal candidate ZrCo2Sn

We report that the partial substitution of Cu for Co has a significant impact on the magnetic properties of the Heusler-phase Weyl fermion candidate ZrCo2Sn. Polycrystalline samples of ZrCo2−xCuxSn (x = 0.0–1.0) exhibited a linearly decreasing ferromagnetic transition temperature and similarly decreasing saturated magnetic moment on increasing Cu substitution x. Materials with Cu contents near x = 1 and several other quaternary materials synthesized at the same x (ZrCoTʹSn (Tʹ = Rh, Pd, Ni)) display what appears to be non-ferromagnetic magnetization behavior with spin glass characteristics. Electronic structure calculations suggest that the half-metallic nature of unsubstituted ZrCo2Sn is disrupted significantly by the Cu substitutions, leading to the breakdown of the magnetization versus electron count guidelines usually followed by Heusler phases, and a more typical metallic non-spin-polarized electronic structure at high x.

Multiple magnetic transitions in MnCo1 − xCuxGe driven by changes in atom separation and exchange interaction

The phase relationships, magnetic transitions, and magnetocaloric effect (MCE) of MnCo1−xCuxGe (x=0–0.5) alloys have been investigated. The substitution of Cu for Co reduces the structural transition temperature between Ni2In-type hexagonal phase and TiNiSi-type orthorhombic phase. The Curie temperature of orthorhombic martensite (TCM) also decreases with increasing x from 0 to 0.2, which is likely due to the weakening of Co-Mn and/or Co-Co interactions by non-magnetic element Cu substitution for Co atoms. In addition, two successive first-order magnetic transitions, a ferromagnetic (FM) to antiferromagnetic (AFM)-like transition around T2 followed by an AFM to FM-like transition around T1, are observed for 0.17≤x≤0.27, which have not been reported in MnCoGe-based alloys so far. An inverse MCE is observed under low field changes and then a universal curve of ΔSM is successfully constructed, proving the applicability of universal curve for AFM materials with inverse MCE. Finally, the variation of magnetic states is explained in terms of the expansion of nearest-neighbor Mn-Mn distance d1. These new findings and related discussions are very helpful for future tailoring of magnetostructural coupling and metamagnetic transition in MM'X (M, M′=transition metals, X=carbon or boron group elements) alloys.

Negative magnetization and zero-field cooled exchange bias effect in Co0.8Cu0.2Cr2O4 ceramics

The negative magnetization and zero-field cooled exchange bias (ZFC EB) effect are observed in Co0.8Cu0.2Cr2O4 polycrystalline ceramics. 20% Cu substitution for Co in CoCr2O4 leads to the evident magnetization reversal at the compensation temperature (Tcomp ∼ 50 K) with applied magnetic field of 500 Oe. Besides, Tcomp decreases monotonously with increasing applied field, and the negative magnetization finally disappears when the field increases to 9000 Oe. Different temperature dependence of sublattice magnetization at different crystallographic sites is proved to induce the magnetization reversal. In addition, ZFC EB effect can be tuned by measuring temperature and presents the maximum of exchange bias field (HEB) with ∼2300 Oe at 50 K. This unconventional EB effect can be attributed to the coupling interaction between the two sublattices.

Mechanochemically assisted solid-state and citric acid complex syntheses of Cu-doped sodium cobaltite ceramics

In the last decade, the sodium cobaltite ceramic became a promising candidate for potential thermoelectric applications, because of its large thermopower and low resistivity. In this work, polycrystalline samples of NaCo2−xCuxO4 (x=0, 0.01, 0.03, 0.05) were prepared using mechanochemically assisted solid-state reaction method (MASSR) and the citric acid complex method (CAC). Bulk samples were prepared by pressing into disc-shaped pellets and subsequently subjected to a thermal treatment at 880°C in inert argon atmosphere. Changes in structural and microstructural characteristics of the samples, caused by the substitution of Cu for Co, were characterized using X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM), respectively. The results of inductively coupled plasma (ICP) analysis showed that the compositions of the final products correspond to γ-NaCo2O4 and confirmed that desired compound was obtained in both syntheses procedures. The advantages and disadvantages of these two syntheses procedures have been observed and discussed: the CAC method enabled obtaining samples with higher density and fine microstructure compared to the MASSR method, thus better thermoelectric properties. The Cu2+ substitution led to the increase in Seebeck coefficient in both synthesis routes. The highest figure of merit of 0.022 at 300K was observed for the sample doped with 1mol% Cu, obtained by the CAC method, and it was almost twice higher than in the undoped sample confirming the significant influence of Cu-doping with even small concentrations.

Enhanced electrochemical activity in Ca3Co2O6 cathode for solid-oxide fuel cells by Cu substitution

Cu-substituted Ca3(Co1−xCux)2O6 (x = 0, 0.05, 0.1, 0.15) are prepared and evaluated as cathode materials for solid-oxide fuel cells (SOFCs). Effects of Cu substitution for Co on structure, electrical conductivity, thermal expansion and electrochemical performance have been investigated. Pure hexagonal structure can be attained, but a small amount of impurity phase Ca0.828CuO2 appears if x is high. Ca3Co2O6 behaves as a thermal-activated semiconductor in the temperature range between 300 and 800 °C; its electrical conductivity is remarkably enhanced by Cu substitution. Experimental results show coexistence of mixed valent Co ions and disordered state of oxygen vacancies in the Cu-substituted samples. Meanwhile, Cu substitution leads to slightly enlarged thermal expansion coefficient, reduced area specific resistance and improved electrochemical performance. For x = 0.05, the power density as high as ca. 550 mW cm−2 at 800 °C is achieved in the single cell with La0.8Sr0.2Ga0.83Mg0.17O2.815 as electrolyte and Ni–Ce0.8Sm0.2O1.9 as anode. Cu substitution can effectively enhance the electronic and ionic transport properties of Ca3Co2O6 cathode for SOFCs.

Effect of stoichiometry and Cu-substitution on the phase structure and hydrogen storage properties of Ml-Mg-Ni-based alloys

To improve the electrochemical properties of rare-earth-Mg-Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the alloys were studied. Nonsubstituted Ml0.80Mg0.20(Ni2.90Co0.50-Mn0.30Al0.30)x (x = 0.68, 0.70, 0.72, 0.74, 0.76) alloys and Cu-substituted Ml0.80Mg0.20(Ni2.90Co0.50−yCuyMn0.30Al0.30)0.70 (y = 0, 0.10, 0.30, 0.50) alloys were prepared by induction melting. Phase structure analysis shows that the nonsubstituted alloys consist of a LaNi5 phase, a LaNi3 phase, and a minor La2Ni7 phase; in addition, in the case of Cu-substitution, the Nd2Ni7 phase appears and the LaNi3 phase vanishes. Thermodynamic tests show that the enthalpy change in the dehydriding process decreases, indicating that hydride stability decreases with increasing stoichiometry and increasing Cu content. The maximum discharge capacity, kinetic properties, and cycling stability of the alloy electrodes all increase and then decrease with increasing stoichiometry or increasing Cu content. Furthermore, Cu substitution for Co ameliorates the discharge capacity, kinetics, and cycling stability of the alloy electrodes.

Tradeoff optimization of electrochemical performance and thermal expansion for Co-based cathode material for intermediate-temperature solid oxide fuel cells

Solid oxide fuel cell (SOFC) is a new electric power generation system with the advantages of high efficiency, no emissions of pollutant, and a wide range of fuels. Layered perovskite oxides have received extensive attention as promising cathode materials for SOFCs because of their faster diffusion coefficient and transport kinetics of oxygen compared to those of ABO3-type perovskite oxides. With the goals of lowering the thermal expansion coefficient (TEC) and maximizing electrochemical properties, this study focuses on the copper (Cu) effect in PrBa0.5Sr0.5Co2-xCuxO5+δ (x=0, 0.5, and 1.0) layered perovskite oxides by investigating their structural characteristics, electrical properties, and electrochemical performance. The electrical conductivity decreases with increasing Cu content, mainly due to the decreasing amount of Co3+/4+. The average TEC values are also identified and the substitution of Cu for Co is beneficial to lower the TEC by suppression of the spin state transitions of Co3+ and reduction of Co4+. To better understand the thermodynamic behavior of the materials while checking redox stability, coulometric titration experiment is performed. We also investigate the electrochemical performance of PrBa0.5Sr0.5Co2-xCuxO5+δ cathode materials using a Ni-GDC anode-supported cell. All samples show sufficiently high power density around over 1.0Wcm−2 at 600°C.

Cofiring behavior of multilayer inductors based on substituted Y- and M-type hexagonal ferrites

Sinter-active soft ferrites with adequate permeability profiles are required for the fabrication of multilayer ferrite inductors (MLFI). For MLFI fabrication, a Low Temperature Ceramic Co-firing (LTCC) process is used. Substituted hexagonal ferrites of Y-, and M-type represent an important family of soft ferrites which might operate at high-frequency conditions up to 2 GHz. However, for Ag-based multilayer inductor applications a sinter process at 900°C is required. Low-temperature sinter-ability is provided by the use of sub-micron powders and/or sintering additives. Substituted Y-type hexagonal ferrites Ba2Co2-x-yZnxCuyFe12O22 were obtained after sintering at 1000°C. Substitution of Cu for Co improved the low-temperature sintering behavior. The addition of 5wt.% Bi2O3 guarantees almost complete densification at 900°C. The saturation magnetization and permeability are significantly affected by the Zn-concentration. A maximum permeability of μ′ = 10 and cut-off frequency fg~2GHz was observed for a ferrite with y = 0.4. Co/Ti-substituted M-type BaFe12-2yCoyTiyO19 ferrites can also be used for multilayer inductors. The magneto-crystalline anisotropy changes from uniaxial to planar upon Co/Ti-substitution, and ferrites with y≥1.1 exhibit soft magnetic behavior. Ferrite powders were prepared at 1000°C. The addition of a sintering aid shifts the temperature of maximum shrinkage down to below 900°C and dense samples were obtained after firing at 900°C. A permeability of μ′ = 16 and a resonance frequency of 1 GHz was observed. Substituted M-type ferrites are stable during co-firing at 900°C and show no sign of decomposition, i.e. these materials are LTCC-compatible. Ferrite tapes were prepared by tape casting and multilayer structures were fabricated by screen printing, stacking, lamination and final co-firing. Firing was performed at LTCC conditions i.e. 900°C. We report on the co-firing behavior, microstructure and permeability of monolithic laminates. It is shown, that hexagonal Co2/Zn2Y- and Co/Ti-M-type ferrites are excellent magnetic materials for multilayer inductors.

Effect of Cu Substitution on the Magnetic Properties of SmCo5 Film with Perpendicular Magnetic Anisotropy

SmCo5 film with perpendicular magnetic anisotropy is a promising candidate ultrahigh-density magnetic recording medium due to its huge magnetocrystalline anisotropy. This paper investigates the effect of Cu substitution for Co on the magnetic properties and microstructure of SmCo5 film by simulations and experiments. The simulation results based on first-principles theory show that Cu substitution for Co in SmCo5 can reduce the total exchange- correlation constant and increase the coercivity of SmCo5 film. Sm(Co,Cu)5/Cu/TiW film samples with different Cu doping were fabricated on quartz glass substrates by radiofrequency (RF) magnetron sputtering, and the dependence of the coercivity of the Sm(Co,Cu)5 film on the Cu doping and annealing conditions was studied. The experimental results demonstrate that Cu doping can decrease the grain size and increase the coercivity of SmCo5 film. By optimizing the sputtering and annealing conditions, perpendicular coercivity of 3796 Oe was obtained in Sm(Co0.72Cu0.28)5 film.

The effect of Cu substitution on microstructure and thermoelectric properties of LaCoO3 ceramics

La(Co, Cu)O(3-δ) ceramics were prepared by pressureless sintering of citrate precursor powders, and their thermoelectric properties were investigated with an emphasis on the influence of Cu doping and phase structure as well as microstructure. It was found that a secondary phase first appeared in the form of a network along the grain boundaries and then changed to dispersion with increasing Cu content, which effectively reduced the lattice thermal conductivity of the materials. The thermal conductivity was only 1.21 W m(-1) K(-1) for the sample LaCo(0.75)Cu(0.25)O(3-δ), being much lower as for the thermoelectric oxide materials. In addition, a small amount of Cu substitution for Co increased the electrical conductivity greatly and the absolute Seebeck coefficient, whose sign was also reversed from negative to positive. The dimensionless figure of merit, ZT, of LaCoO(3-δ) oxides at low and middle temperatures can be remarkably enhanced by substituting Co with Cu.

Effects of annealing treatment and partial substitution of Cu for Co on phase composition and hydrogen storage performance of La 0.7Mg 0.3Ni 3.2Co 0.35 alloy

In this paper, the phase composition, hydrogen absorption/desorption as well as electrochemical characteristics of as-cast and annealed La 0.7Mg 0.3Ni 3.2Co 0.35− X Cu X alloys were investigated by X-ray diffraction (XRD), pressure composition isotherm (PCT) and electrochemical measurements. The results showed that La 2Ni 7 phase and LaNi phase coexisted in the as-cast alloys, but only La 0.98Ni 5.10 phase was detected in the annealed alloys. The maximum and reversible hydrogen storage capacities of the annealed alloys were higher than that of as-cast alloys, with greatly improved plateau performance. The substitution of Cu for Co made the electrochemical discharge capacity of the annealed alloys lower than that of as-cast alloys.

High-temperature Thermoelectric Properties of Cu-substituted Bi 2Ba 2Co 2- xCu xO y Oxides

Cu-substituted Bi 2 Ba 2 Co 2- x Cu x O y (0.0≤ x ≤0.4) samples were prepared by conventional solid-state reaction method and the effect of Cu substitution on the microstructure and thermoelectric properties were investigated. The partial substitution of Cu for Co in Bi 2 Ba 2 Co 2- x Cu x O y led to an increase in the electrical conductivity because of an increase in the hole concentration and grain size of sintered bodies. In addition, Cu substitution led to an increase in Seebeck coefficients while kept the thermal conductivity unchanged. The highest thermoelectric figure of merit (ZT value) was obtained in x =0.4 sample and the value was 1.5 times as large as that of Cu-free sample at 873 K.

Study on the structure and hydrogen storage characteristics of as-cast La 0.7Mg 0.3Ni 3.2Co 0.35−XCu X alloys

In this paper, the structure, hydrogen storage performance, electrochemical discharge and cyclic characteristics of La 0.7Mg 0.3Ni 3.2Co 0.35−XCu X alloys were investigated using X-ray diffraction (XRD), pressure composition isotherm (PCT) and electrochemical tests. XRD tests showed that all of the alloys were composed of La 2Ni 7 and LaNi phases. The ratio of LaNi phase in these alloys increased with increasing substitution of Cu for Co. PCT tests showed that increasing substitution of Cu for Co resulted in the decrease of hydrogen storage capacity and the increase of plateau pressure. Electrochemical discharge tests showed that the discharge capacity increased first and then decreased with increasing substitution of Cu for Co.

Enhanced high temperature thermoelectric characteristics of transition metals doped Ca3Co4O9+δ by cold high-pressure fabrication

A series of Fe, Mn, and Cu doped Ca3Co4O9+δ samples, Ca3(Co,M)4O9+δ (M=Fe, Mn, and Cu), were fabricated by cold high-pressure compacting technique. Their thermoelectric properties were investigated from room temperature up to 1000 K. The cold high-pressure compacting method is advantageous to increasing density and texture, in favor of the improvement of thermoelectric performance. The electrical transport measurements indicate that Fe/Mn substitutes for Co mainly in [CoO2] layers whereas the substitution of Cu for Co takes place in [Ca2CoO3] layers. The thermoelectric properties as well as electronic correlations depend not only on the substitution ion but also the Co site that is replaced. Thermopower can be well calculated by the carrier effective mass according to Boltzmann transport model, indicating that the electronic correlation plays a crucial role in the unusual thermoelectric characteristics of this system. From the changes in thermopower, resistivity, and thermal conductivity, thermoelectric performance of Ca3Co4O9+δ is efficiently improved by these transition metals doping. Fe doped samples possess the highest ZT values. Combining cold high-pressure technique, ZT of Ca3Co3.9Fe0.1O9+δ can reach ∼0.4 at 1000 K, which is quite large among ceramic oxides, suggesting that Fe doped Ca3Co4O9+δ could be a promising candidate for thermoelectric applications at elevated temperatures.

Influence of partial substitution of Cu for Co on the thermoelectric properties of NaCo 2O 4

Cu-substituted Na(Co 1− y Cu y ) 2O 4 (0 ≤ y ≤ 0.2) polycrystalline samples have been prepared using a solid-state reaction method and their thermoelectric properties studied. The electrical conductivity of Na(Co 1− y Cu y ) 2O 4 decreased with increasing temperature, indicating metallic behavior. The electrical conductivity ( σ) of Cu-substituted Na(Co 1− y Cu y ) 2O 4 was much higher than that of Cu-free NaCo 2O 4. In addition, the Seebeck coefficient ( α) of Na(Co 1− y Cu y ) 2O 4 increased with increasing temperature and the Cu substitution led to an increase in the Seebeck coefficient. The power factor ( σα 2) increased with an increase in temperature and the highest value of power factor (3.08 × 10 −3 W m −1 K −2) was attained for Na(Co 0.9Cu 0.1) 2O 4 at 1073 K. We demonstrate that the Cu substitution is effective for enhancing thermoelectric properties.

Microstructure and high-temperature thermoelectric properties of CuO and NiO co-substituted NaCo 2O 4

The partial substitution of Cu for Co in Na(Co 1− z Ni z ) 2O 4 (0 ≤ z ≤0.15) led to an increase in the electrical conductivity ( σ) mainly because of an increase in the hole concentration, density, and grain size of sintered bodies. On the other hand, the partial substitution of Ni for Co in Na(Co 1− y Cu y ) 2O 4 (0 ≤ y ≤ 0.15) gave rise to a decrease in the electrical conductivity mainly because of a decrease in the density and grain size. In particular, the Cu and/or Ni substitution led to a significant increase in the Seebeck coefficient ( α). The power factor ( σα 2) was substantially improved by the partial co-substitution of Cu and Ni for Co in NaCo 2O 4. The highest value of power factor (3.27 × 10 −3 Wm −1 K −2) was attained for Na(Co 0.7Cu 0.15Ni 0.15) 2O 4 at 1073 K. It is concluded that the Cu and Ni co-substitution is effective for enhancing high-temperature thermoelectric properties.