Small Amount Of Cu Research Articles

Doping effects on the thermoelectric properties of Cu-intercalated Bi2Te2.7Se0.3

We herein report an enhancement of the thermoelectric performance of spark plasma sintered polycrystalline n-type Bi2Te2.7Se0.3 by the intercalation of Cu and the doping of Al on Bi-sites. Through the intercalation of a small amount of Cu (0.008), the reproducibility could be significantly improved, with ZT was enhanced from 0.64 to 0.73 at 300 K due to the reduced lattice thermal conductivity benefiting from intensified point-defect phonon scattering. We also found that Al is an effective doping element for power factor enhancement and for reducing the lattice thermal conductivity of Cu-intercalated Bi2Te2.7Se0.3. With these synergetic effects, an enhanced ZT values of 0.78 at 300 K and 0.81 at 360 K were obtained in 1 at% Al-doped Cu0.008Bi2Te2.7Se0.3 (Cu0.008Bi1.98Al0.02Te2.7Se0.3).

Durable Cu composite catalyst for hydrogen production by high temperature methanol steam reforming

Durable catalysts are necessitated for the high temperature methanol steam reforming in compact hydrogen processors. The high durability at 400 °C can be obtained with a composite Cu catalyst where a small amount of Cu–ZnO–ZrO2–Y2O3–In2O3 is coprecipitated on a zirconia support. The lifetime of the composite catalyst containing 3 wt.% Cu is estimated to be as long as 53 × 102 h at 400 °C to produce the full conversion at a contact time of 250 g h m−3. The deactivation rate empirically relates to the cube of the activity. The gradual deactivation is caused by the gradual reduction of the Cu surface amount and also by the reduction of the surface activity which is believed to decrease with an increase in the Cu particle size. The interaction between the thin layer of the coprecipitate and the support surface probably suppresses the aggregation of the coprecipitate leading to Cu sintering.

Promoting effect of a Cu–Zn binary precursor on a ternary Cu–Zn–Al catalyst for methanol synthesis from synthesis gas

Small amounts of Cu–Zn binary precursor were introduced into traditional ternary Cu–Zn–Al catalysts to produce a series of modified ternary Cu–Zn–Al catalysts for the synthesis of methanol from synthesis gas with high CO content. 2 wt% Cu–Zn (Cu–Zn = 3 : 1 atomic ratio) binary precursor was found to have the most significant improvement for the catalytic performances. Physicochemical characterization of the as-prepared catalysts by TPR, in situ XRD and in situ XAES techniques indicated that the addition of a suitable amount of binary Cu–Zn precursor partially modified the structure of the catalyst, changed the particle size of Cu, copper surface area and the ratio of Cu+/Cu0, and thus effectively improved the catalytic performances of the catalyst.

Laser cladding of FeCoNiCrAlCuxSi0·5 high entropy alloys on AZ31 Mg alloy substrates

To improve the inherent low hardness and poor corrosion resistance of an AZ31 Mg alloy, FeCoNiCrAlCuxSi0·5 high entropy alloys (HEAs) were clad on Mg alloy substrates using a pre-placed powder bed method and laser re-melting. The results showed that coating dilution by Mg was limited to the interface regions. Similarly, except for a small amount of Cu of the HEA entering into the Mg substrate to a shallow depth, no other HEA elements were found in the re-melted zone of the substrate. The stability of FeCoNiCrAlCuxSi0·5 HEAs with the addition of Mg was evaluated based on the change of the Gibbs free energy. The results showed that the original HEAs without Mg were stable alloys. The microstructure of the FeCoNiCrAlCuSi0·5 and FeCoNiCrAlCu0·5Si0·5 clads consisted of only bcc and fcc simple solid solution phases without intermetallic compounds. With regard to properties, the HEA clads have high hardness and high corrosion resistance.

Superior catalytic performance of non-stoichiometric solid solution Ce1 − xCuxO2 − δ supported copper catalysts used for CO preferential oxidation

A series of Ce1−xCuxO2−δ non-stoichiometric solid solutions and their supported copper catalysts CuO/Ce1−xCuxO2−δ (x=0, 0.005, 0.022, 0.043) were prepared by co-precipitation and deposition–precipitation, respectively. The CuO/Ce1−xCuxO2−δ catalysts show high performance for CO preferential oxidation (CO PROX). Multiple techniques of N2 sorption (BET), XRD, Laser Raman spectroscopy (LRS), HRTEM, H2-TPR, O2-TPO, N2O chemisorption and in-situ DRIFTS were used for catalyst characterization. The results of XRD, LRS and H2-TPR conformably indicate that a small amount of Cu2+ ions can be incorporated into the lattice of CeO2, forming non-stoichiometric solid solutions Ce1−xCuxO2−δ, which shows much better reducibility than pure CeO2. The supported CuO/Ce1−xCuxO2−δ catalysts exhibit remarkably enhanced activity for CO PROX as compared with CuO/CeO2, especially the catalyst CuO/Ce0.978Cu0.022O2−δ containing 15% Cu, which displays the best CO PROX performance, showing not only the lowest temperature (115°C) for CO total conversion, but also the 100% selectivity of O2 to CO2 at this temperature. Several aspects including the presence of more oxygen vacancies, the improved reducibility, and stronger capability for CO chemisorption of this catalyst account well for its superior performance for CO PROX. Based upon the in-situ DRIFTS study, it is revealed that Cu+ is the main active site for CO oxidation, while Cu0 is more active for H2 activation and oxidation.

Activating ZnO nanorod photoanodes in visible light by Cu ion implantation

Utilization of visible light is of crucial importance for exploiting efficient semiconductor catalysts for solar water splitting. In this study, an advanced ion implantation method was utilized to dope Cu ions into ZnO nanorod arrays for photoelectrochemical water splitting in visible light. X-ray diffraction (XRD) and X-ray photo-electron spectroscopy (XPS) results revealed that Cu+ together with a small amount of Cu2+ were highly dispersed within the ZnO nanorod arrays. The Cu ion doped ZnO nanorod arrays displayed extended optical absorption and enhanced photoelectrochemical performance under visible light illumination (λ > 420 nm). A considerable photocurrent density of 18 μA/cm2 at 0.8 V (vs. a saturated calomel electrode) was achieved, which was about 11 times higher than that of undoped ZnO nanorod arrays. This study proposes that ion implantation could be an effective approach for developing novel visible-light-driven photocatalytic materials for water splitting. Open image in new window

TiO2 thin film crystallization temperature lowered by Cu-induced solid phase crystallization

We lowered the crystallization temperature of amorphous TiO2 thin films using a Cu catalyst as either a bottom or cap layer. The Cu bottom layer reduced the crystallization temperature of TiO2 by ~30°C. Depth profile analyses by Rutherford backscattering spectrometry revealed that a very small amount of Cu was sufficient to induce full crystallization of the TiO2 film. Depositing the Cu cap layer and annealing at 210°C for 3h yielded a transparent anatase TiO2 thin film upon wet-etching the Cu cap.

Understanding strong magnetostriction in Fe100−xGax alloys

Magnetostriction of ferromagnetic materials describes the change of their shape or dimension in response to the reorientation of magnetization under the influence of external magnetic field. Fe100−xGax binary alloys (Galfenol) have large magnetostriction and excellent ductility; and they are very promising rare-earth free materials for applications in sensors, actuators, energy-harvesters and spintronic devices. Here we report results of large-scale ab initio molecular dynamics (AIMD) simulations for Galfenol, especially regarding the mechanism that leads to the sudden drop of tetragonal magnetostriction at x ~ 19, a long-standing puzzle for the community. Based on rigid band analysis, we propose possible ways to further optimize the performance of Galfenol for device applications. For example, we found that the substitution of a small amount of Cu for Ga (1.6%) in certain configuration may double the magnetostriction of Galfenol.

Effect of Current Density on Microstructure of Mn-Cu Thin Films via Electroplating Coating Technique

In the present study 304 stainless steel (SS) was electrochemical plated with nanocrystallineMn-Cu alloy coatings from a bath containing ammonium sulfate.The electrochemical investigation of Mn-Cu electrodeposited films was managed by potentiodynamic scans and galvanostatic experiments. The effect of current density on the microstructure, crystallographic structure, and chemical composition of the deposits were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive x-ray spectrometry (EDS), respectively.The results showed that Mn-Cu coatings obtained at low current density contain a large amount of Cu and heterogeneous microstructure, while at high current density uniform, compact, and amorphous coatings with a small amount of Cu was obtained. The results indicated that Cu co-deposition delayed the phase transformation of as-deposited ductile γ-Mn to the brittle and hard α-Mn. However, the results did not show any specific changes in grain size of the coatings with variation of current densities.

Structure and magnetism of epitaxial SrTi0.78Cu0.22O3−δ films with mixed-valence Cu ions

The structure and magnetic behavior of Cu-substituted Sr2+Ti4+O3-δ (STCu) thin films with ∼22% Cu on the Ti sites, grown on CeO2/yttria stabilized zirconia buffered (001) Si substrates were investigated. STCu films grew with (110) orientation or with a mixed (001)+(110) orientation and were under in-plane compressive strain. They showed weak room temperature ferromagnetism with a saturation magnetization of 0.3 ∼ 1.7 emu/cm3. Cu ions in STCu grown in an oxygen atmosphere existed mainly as Cu3+ with a small proportion of Cu2+, while in STCu grown in vacuum, Cu1+ ions were dominant with small amounts of Cu2+ and Cu3+. The saturation magnetization was attributed to the Cu2+ (3d9, S = 1/2) concentration, and the majority of Cu3+ (3d8, S = 0) ions were stabilized in the low-spin diamagnetic electron configuration similar to that found in mixed-valence layered perovskite superconductor compounds.

Copper binding by terrestrial versus marine organic ligands in the coastal plume of River Thurso, North Scotland

It is generally assumed that terrestrial humic matter contains a high density of metal complexing ligands spanning a wide range of stability constants. From equilibrium modelling it would be anticipated that carboxyl groups, which are known to be abundant in humic matter, should be capable of binding Cu quantitatively in humic-rich estuarine systems such as the river plume outflow of River Thurso, on Scotland's north coast, where concentrations along the full mixing gradient typically range for Cu: 1−25 nM and for DOC (Dissolved Organic Carbon): 150−1500 μM. Using a combination of reverse and forward titrations monitored by adsorptive cathodic stripping voltammetry (ACSV), we show that terrestrial humic substances were the likely source of high-affinity (class 1), low abundance ligands (1−4 nM) found throughout the coastal plume, but that weaker (class 2), more abundant ligands (90−170 nM) appeared to be produced largely in situ, probably as a biological response to Cu inputs into the estuary. Conditional stability constants for Cu-binding were respectively log K1′ = 14.9–15.9 and log K2′ = 11.8–12.6. Class 2 ligands were evenly distributed between the low and high molecular weight fractions of dissolved organic matter (DOM), both in March and May. Class 1 ligands were more abundant in the low molecular weight fraction in March, but not in May. The latter could be related to seasonal differences in the nature of peatland derived organic matter carried by River Thurso. Since class 1 ligands (terrestrial, humic) were saturated with Cu throughout the plume, it effectively fell upon class 2 ligands (marine, biological) to control Cu speciation in Thurso Bay, in particular keeping the free Cu concentration [Cu2+] within a relatively narrow range (10−13.6 M to 10−12.4 M). On the other hand, class 1 ligands were responsible for solubilising small amounts of Cu derived from this peatland catchment and effectively transporting Cu, in dissolved and colloidal forms, to the ocean.

Effect of current density and electrolyte pH on microstructure of Mn–Cu electroplated coatings

In the present study 304 stainless steel (SS) was electrochemically plated with nanocrystalline Mn–Cu alloy coatings from a bath containing ammonium sulfate. The electrochemical investigation of Mn–Cu electrodeposited films was managed by potentiodynamic scans and galvanostatic experiments. The effect of pH and current density on the microstructure, cathodic efficiency, crystallographic structure, and chemical composition of the deposits were characterized by means of scanning electron microscopy (SEM), weight gain measurements, X-ray diffraction (XRD), and energy dispersive X-ray spectrometry (EDS), respectively. The results showed that Mn–Cu coatings obtained at low current density contain a large amount of Cu and a heterogeneous microstructure, while at high current density uniform, compact, and amorphous coatings with a small amount of Cu was obtained. The XRD and SEM analyses of the films showed that the deposition of Mn–Cu alloy is more affected by the current density than electrolyte pH. However, the results did not show any specific changes in the grain size of the coatings with variation of current densities. The results indicated that Cu co-deposition delayed the phase transformation of as-deposited ductile γ-Mn to the brittle and hard α-Mn.

Influence of Copper Addition on Glass Forming Ability, Thermal Stability, Structure and Magnetic Properties of Fe-Co-Based BMGs

The aim of the paper was investigation of the effect of Cu addition on glass forming ability (GFA), thermal stability, structure and magnetic properties of Fe-Co-based bulk metallic glasses (BMGs). The raw materials used in this experiment for the production of BMGs were pure Fe, Co, Cu and industrial Fe-B, Fe-Si, Fe-Nb ferroalloy. Investigations were carried out on BMGs in rods shaped with square section with side of 1.5mm. The structure of the investigated BMGs in rod form is amorphous. The addition of small amounts of Cu is effective in changing GFA and magnetic properties. The melting temperature - Tm remained almost constant for both investigated alloy. Two alloy compositions are at or very close to the eutectics, what according to ref. [1] should guarantee the best metallic glass-forming alloys. The investigated alloys have good soft magnetic properties. The successful synthesis of the Fe36.00Co36.00B19.00Si5Nb4 and Fe35.75Co35.75B18.90Si5Nb4Cu0.6 alloys with high GFA and good soft magnetic properties by using starting industrial alloys are encouraging for the future industry applications.

Characterization of the austemperability of partially austenitized ductile iron

This study focuses on the characterization of the hardenability and the austemperability of partially austenitized ductile iron melts alloyed with small amounts of Cu, Ni and Mn.The hardenability was studied by using Jominy tests. The results show that the hardenability of partially austenitized ductile iron samples is significantly lower than that found on the fully austenitized samples. The partially austenitized samples do not show an initial plateau of hardness. This behavior can be caused by the presence of ferrite in the matrix before cooling. This ferrite facilitates the epitaxial growth of new ferrite during cooling, which may account for the drop in hardness and the poor hardenability.The austemperability was measured on round bars after austempering in a molten salt bath. The metallographic studies show that full dual phase microstructure could be obtained only at the smaller diameter rods. As the rod diameter becomes larger, pearlite precipitates. The cooling rate for the advent of pearlite precipitation identified in the Jominy hardenability tests was compared with that observed on the austempering treatments, observing a good correlation.It is proposed that the behavior of ductile iron austempered from partial austenitizing temperatures can be predicted with good accuracy by measuring the cooling rate for the onset of pearlite precipitation on Jominy tests.

LaNi1 − x Cu x O3 (x = 0.05, 0.10, 0.30) coated electrodes for oxygen evolution in alkaline medium

LaNi1 − xCuxO3 (x = 0.05, 0.10, 0.30) coated electrodes were prepared by brush painting using Ni foam substrates in order to increase its active surface area. For comparison, coatings with x = 0.05 were also prepared using vitreous carbon substrates. Cyclic voltammetry was used to evaluate the coating roughness (Rf). Values between 5,145 ± 148 and 6,334 ± 277 were obtained, depending on the x value, for the coatings on Ni foam. These results show that the electrodes prepared with LaNi1 − xCuxO3 powder, obtained at 600 °C, lead to a big increase on the oxide electrode roughness when compared with LaNiO3 electrodes prepared by a similar method. Much lower values were obtained for the coatings on vitreous carbon indicating that the substrate nature is also a key factor for the preparation of high surface area electrodes. The calculated kinetic parameters for the oxygen evolution reaction (OER) show that the partial replacement of Ni by Cu has no beneficial effect on the intrinsic catalytic activity of the coatings. On the other hand, a big increase on the active area is observed even for small amounts of Cu (x = 0.05), leading to a better overall OER performance for the LaNi0.95Cu0.05O3 coating on Ni foam. For this composition, the activity is dominated by geometric effects.

Enhanced sintering behavior mechanism of nanocrystalline BaCe0.8Sm0.2O3−δ by Cu doping

Nano-sized BaCe0.8Sm0.2O3−δ and Cu-doped BaCe0.8Sm0.2O3−δ proton conducting electrolyte powders are synthesized by citric-nitrate method, and then the powder properties are investigated. The synthesized BaCe0.8Sm0.2O3−δ powder acquires pure perovskite structure after heat treatment above 1100 °C, while impurity phases such as BaCO3 and Ce0.8Sm0.2O2−δ are formed below 1100 °C. The BaCe0.8Sm0.2O3−δ and Cu-doped BaCe0.8Sm0.2O3−δ showed similar powder characteristics, except the shrinkage rate. The sintering temperature for densification of the synthesized BCS are significantly reduced as much as ∼300 °C by small amount of Cu. Compared to drastic reduction in sintering temperature, the total conductivity and the activation energy of Cu doped BCS turn out to deviate negligibly from those of pure BCS.

Ab Initio Calculation of the Gilbert Damping Parameter via Linear Response Formalism

A Kubo-Greenwood-like equation for the Gilbert damping parameter α is presented that is based on the linear response formalism. Its implementation on the basis of the fully relativistic Korringa-Kohn-Rostoker (KKR) band structure method together with the Coherent Potential Approximation (CPA) alloy theory allows application to a wide range of situations. This is demonstrated by results obtained for the alloy system bcc Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> as well as for a series of alloys of permalloy with 5 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> transition metals. To account for the thermal displacements of atoms as a scattering mechanism, an alloy-analogy model is introduced. In line with experiment, calculations for Ni correctly describe the rapid change of α when small amounts of Cu are introduced substitutionally.

Effect of Cu by Co substitution on Ca3Co4O9 thermoelectric ceramics

Ca3Co4−xCuxO9 polycrystalline thermoelectric ceramics with small amounts of Cu have been synthesized by the classical solid state method. X-ray diffraction data have shown that all the Cu has been incorporated into the Ca3Co4O9 structure and no Cu-containing secondary phases have been produced. Apparent density measurements have shown that all samples are very similar, with densities around 75 % of the theoretical one. Electrical resistivity decreases when Cu content increases until x = 0.03 while Seebeck coefficient remains practically constant for all samples. The improvement in resistivity leads to higher power factor values than the obtained for the undoped samples.

Evaluation of Ni-free Zr–Cu–Fe–Al bulk metallic glass for biomedical implant applications

This study was conducted to investigate the surface characteristics, including the chemical composition, metal ion release, protein adsorption, and cell adhesion, of a Ni-free Zr-based (Zr62.5Cu22.5Fe5Al10) bulk metallic glass (BMG) with low elastic modulus for biomedical implant applications. X-ray photoelectron spectroscopy was used to identify the surface chemical composition and the protein (albumin and fibronectin) adsorption of the specimen. The metal ions released from the specimen in simulated blood plasma and artificial saliva solutions were measured using an inductively coupled plasma-mass spectrometer. The cell adhesion, in terms of the morphology, focal adhesion complex, and skeletal arrangement, of human bone marrow mesenchymal stem cells was evaluated using scanning electron microscope observations and immunofluorescent staining. For comparison purposes, the above-mentioned tests were also carried out on the widely used biomedical metal, Ti. The results showed that the main component on the outermost surface of the amorphous Zr62.5Cu22.5Fe5Al10 BMG was ZrO2 with small amounts of Cu, Al, and Fe oxides. The released metal ions from Zr62.5Cu22.5Fe5Al10 BMG were well below the critical concentrations that cause negative biological effects. The Zr62.5Cu22.5Fe5Al10 BMG had a greater adsorption capacity for albumin and fibronectin than that of commercial biomedical Ti. The Zr62.5Cu22.5Fe5Al10 BMG surface showed an attached cell number similar to the Ti surface but had better cell adhesion morphology and cytoskeletal arrangement. Based on the present results, the Ni-free Zr62.5Cu22.5Fe5Al10 BMG has the potential to be used for biomedical implant applications.

Cu induced morphology changes at Pb/Si (1 1 1) interface: Separation of “5 × 5”-Cu structure into individual domains

The adsorption of small amount of Cu onto 1×1-Pb/Si (111) and √3×√3R30°-Pb/Si (111) coexisting phases was studied with variable temperature scanning tunnelling microscopy and spectroscopy. The most significant features connected with the deposition of copper at room temperature appeared as tiny clusters randomly scattered over smooth 1×1-Pb islands. Behaviour of the clusters at room at low temperature assumed that Cu penetrates through inert 1×1-Pb layer and mixes up with silicon. Moderate thermal treatment of (Cu, Pb)/Si (111) system induced the formation of shallow depressions of variable shape and size that are embedded into 1×1-Pb phase. Tunnelling spectra taken over a particular depression showed the peaks typical for the copper silicides. Moreover, the temperature rise causes the formation of large objects of distinctive hexagonal shape on neighbouring √3×√3R30°-Pb/Si (111) structure. Filled and empty state STM images of the hexagons differ strongly suggesting covalent bonding between constituent atoms. Detailed analysis of the hexagonal objects (and their agglomerates) reveals the specific features of quasi-commensurate 5×5-Cu structure.