Effect Of Cu Substitution Research Articles

Layered LnBaCo2 − xCuxO5 + δ ( 0 ⩽ x ⩽ 1.0 ) Perovskite Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells

The effects of Cu substitution on the crystal chemistry, thermal and electrical properties, and catalytic activity for the oxygen reduction reaction of the layered ( and Gd, and ) perovskite have been investigated. The compositions exhibit thermal expansion coefficients (TEC) of for and for in the range of . The ( for and for ) cathodes exhibit low polarization resistance and fuel cell performance comparable to that of the well-known perovskite cathodes, but with an important advantage of lower TEC. The better performance of these Cu-substituted samples is partly due to the improved chemical stability with the electrolyte at high temperatures and a better matching of the TEC value with those of the standard electrolytes. With an electrolyte-supported single cell configuration , and exhibit higher maximum power densities of, respectively, 772 and at compared to that of the Cu-free sample (658 and ).

Superconducting fluctuation behavior and infrared absorption properties of Tl1−Cu Sr1.6Yb0.4CaCu2O7 and Tl0.5Pb0.5Sr2−Mg Ca0.8Yb0.2Cu2O7− ceramics

Abstract In this paper, the effects of Cu substitution at Tl site in Tl1−xCuxSr1.6Yb0.4CaCu2O7−δ (x = 0–0.5) ceramics and Mg substitution at Sr site in Tl0.5Pb0.5Sr2−yMgyCa0.8Yb0.2Cu2O7−δ ceramics, respectively on superconducting and structural properties are reported. Excess conductivity analyses based on Asmalazov–Larkin (AL) theory revealed 2D–3D transition and showed Cu substitution affects the A3D constant and increases c-axis coherence length, ξc(0). FTIR analysis for Tl1−xCuxSr1.6Yb0.4CaCu2O7−δ (x = 0–0.5) showed CuO2 planar oxygen mode observed around 578.7 cm−1 in the x = 0 sample was softened to 570 cm−1 with increased Cu substitution indicating enhanced coupling between CuO2 planes. On the other hand, Tl0.5Pb0.5Sr2−yMgyCa0.8Yb0.2Cu2O7−δ (y = 0–1.0) showed increasing semiconductor-like normal state behavior and gradual suppression of Tc with Mg. Excess conductivity analyses of Tl0.5Pb0.5Sr2−yMgyCa0.8Yb0.2Cu2O7−δ (y = 0) showed exclusively 1D–2D transition behavior. FTIR absorption data indicate possible tilt of oxygen atoms in the CuO2 plane as a result of unequal bond lengths of Pb–OA–Cu(2) and Tl–OA–Cu(2) and enhanced CuO2 inter-plane coupling. Superconductivity in both series is explained in terms interplay between the effect of increased inter-plane coupling on ξc(0) and hole concentration in CuO2 planes.

Effects of Cu substitution on superconductivity and excess conductivity of Tl1–xCuxSr1·8Yb0·2CaCu2O7–δ (x=0–0·6) ceramics

TlSr1212 samples were synthesised from Tl1–xCuxSr1·8Yb0·2CaCu2O7–δ (x=0·0 to 0·6) starting composition using the solid state synthesis method. Temperature dependent electrical resistance measurements showed gradual change of normal state resistance behaviour from metallic (x=0·0 to 0·3) to semimetallic (x=0·4) and to semiconductor-like behaviour (x=0·5 to 0·6). The best superconducting behaviour for the series was observed at x=0·4 with zero resistance critical temperature Tc zero of 77·6 K. The effects of Cu substitution on superconducting properties are discussed in terms of the concept of average Cu valence. In addition, excess conductivity behaviour was analysed using Asmalazov–Larkin theory to study the effect of Cu substitution on superconductivity fluctuation behaviour. The analysis showed characteristic cross-over from two-dimensional to three-dimensional behaviour with decreasing temperature.

High Pressure Synthesis of Novel Mg(Ni<SUB>1−<I>x</I></SUB>Cu<I><SUB>x</SUB></I>)<SUB>2</SUB> Hydrides (<I>x</I>=0–0.2)

MgCu, 14) and Mg50Cu21 14) by using this method. In our previous study, MgNi2 (C36) was hydrogenated under a hydrogen pressure of the order of gigapascals rather than ambient hydrogen pressure. 15) The hydrogen content of a novel MgNi2 hydride was estimated to be 2.23 mass% and their dehydrogenation temperature was approximately 460 K, which is approximately 100 K lower than those of MgH2 and Mg2NiH4. Moreover, Mg(Ni1� xCux)2 (x ¼ 0{0:2) was found to be hydrogenated, 14) but the optimum condition of hydrogenation of Mg(Ni1� xCux)2 was not investigated. Therefore, in this study, the optimum condition for hydrogenating Mg(Ni1� xCux)2 (x ¼ 0:0{0:3) intermetallics was investigated. The effects of Cu substitution on their crystal structures, thermal stabilities and hydrogen contents of Mg(Ni1� xCux)2 (x ¼ 0:0{0:3) hydrides were also investigated. 2. Experimental Procedures

Conductivity and dielectric studies of copper–aluminate substituted spinel nickel ferrite

Abstract Effect of Cu substitution in the spinel ferrite Ni 1− x Cu x Al 0.6 Fe 1.4 O 4 (0.0 ≤ x ≤ 1.0) in steps of 0.25 has been studied. Electrical measurements in the frequency range 10 2 –10 5 Hz and at temperature between 300 and 600 K show that these materials have a semiconductor-to-metallic transition as copper content increases. All studied compositions exhibit a transition with a change in the slope of the conductivity versus temperature curve. Dielectric parameters of these materials were studied as a function of frequency and temperature, where the dielectric permittivities ( ɛ ′, ɛ ″) revealed a dielectric anomaly at the transition temperature T c . The obtained T c is found to decrease with increasing Cu concentration. Relaxation spectrum was obtained in the relation of dielectric loss tangent (tan δ ) with frequency for sample with ( x = 0.5) where relaxation time τ and the maximum frequency ν ∞ of the hopping conduction mechanism is obtained. The variation of ( ɛ ′, ɛ ″ and tan δ ) with frequency and temperature displays a strong dependence on both nickel and copper concentrations. The results are explained in light of the cation–anion–cation and cation–cation interactions over the octahedral site in the spinel structure.

On the evolution of quasicrystalline and crystalline phases in rapidly quenched Al-Co–Cu–Ni alloy

The occurrence of stable decagonal quasicrystalline phase in Al–Co–Ni and Al–Cu–Co alloys through conventional solidification is well established. Earlier, we have studied the effect of Cu substitution in place of Co in the Al 70Co 15Ni 15 alloy. Here we report the structural/micro-structural changes with substitution of Cu for Ni in rapidly solidified Al–Co–Ni alloys. The melt spun ribbons have been characterized using X-ray diffractometry, scanning and transmission electron microscopy. With an increase in Cu content in the melt spun Al 70Co 15Cu x Ni 15− x ( x = 0–15 at.%) alloys, the relative amount of the decagonal phase decreased up to 10 at.% of Cu. At this composition, the quaternary alloy showed the co-existence of decagonal quasicrystal and superstructure of τ 3 vacancy ordered crystalline phases. The decagonal phase containing Cu showed more disordering than Al–Co–Ni alloys. The implication of the structural and microstructural changes due to Cu substitution in stable decagonal quasicrystals will be discussed.

Effect of Cu substitution on the structural and magnetic properties of [formula omitted

We present here the results on the effect of Cu substitution in DyCo 5 - x Cu x ( x = 0 , 1 , 2 , 3 ) compounds, studied using structural and magnetization measurements on polycrystalline samples. All the samples are ferrimagnetic in nature and the Curie temperature decreases with increase in Cu concentration. The easy magnetization direction at room temperature lies in the ab-plane, which suggests that there is no considerable increase in the axial anisotropy with Cu substitution.

Effect of Cu Substitution on Thermoelectric Properties of Ge Clathrates

We have prepared polycrystalline n-type Ba 8 Cu x Ga y Ge 4 6 - x - y (x = 0-5, y = 16 - 3x) clathrate compounds by arc melting and spark plasma sintering techniques and investigated the effect of Cu substitution for Ge on their thermoelectric properties. The Hall carrier concentration for Cu-substituted compounds is almost constant at the order of 10 2 0 cm - 3 , which is comparable to that for Ba 8 Ga 1 6 Ge 3 0 stoichiometric compounds. The Seebeck coefficient for these compounds is comparable to that for n-Ba 8 Ga y Ge 4 6 - y compounds. From the analysis of the properties, the effective mass of the conduction band is estimated to be about 1.4 m 0 , which is equivalent to or slightly smaller than that of n-Ba 8 Ga y Ge 4 6 - y compounds. The Hall mobility increases as the Cu composition increases. Its temperature dependence obeys approximately 7 - 1 / 2 dependence in the range of 80-300 K, indicating the dominance of the alloy disorder scattering. Two models are discussed to account for the reduction in the alloy disorder scattering by Cu substitution.

Crystal structure and magnetic properties of PrCo6.8−xCuxHf0.2 compounds

The effects of Cu substitution on the crystal structure and magnetic properties of PrCo6.8−xCuxHf0.2 (x = 0–1.0) compounds were investigated by means of x-ray powder diffraction and magnetic measurements. The as-cast PrCo6.8−xCuxHf0.2 compounds crystallize in the TbCu7-type structure with the space group P6/mmm. The Curie temperature and magnetic anisotropy field decrease with increasing Cu content. A spin reorientation behaviour has been observed in the PrCo6.8−xCuxHf0.2 compounds. The addition of Cu weakens the anisotropy of the Co sublattice, leading to an increase in the spin reorientation temperature with increasing content of Cu.

Effect of Cu substitution in Al–Co–Ni decagonal quasicrystals

A stable decagonal phase has been observed in both as-cast and rapidly solidified Al–Co–Ni and Al–Co–Cu alloys, which form in the composition range of 15–20 at.% Co and 10–15 at.% Ni or 15–20 at.% Cu. In the present investigation, copper was substituted for Co and Ni in Al 70Co 15Ni 15. Compositions corresponding to Al 70Co 15− x Cu x Ni 15 and Al 70Co 15Cu x Ni 15− x were investigated. It is found that when the copper concentration reaches a value of 5 at.%, the disorder marker, i.e. the streaking along the 111,113 rows becomes predominant. For Al 70Co 15− x Cu x Ni 15, when all of the Co is replaced by Cu, the decagonal phase disappears and the only phase observed is the vacancy ordered phase. In Al 70Co 15Cu x Ni 15− x when the Cu concentration reaches a value of 10 at.%, the decagonal and crystalline phases coexist.

Effect of Cu-substitution on the conductivity of Ag-rich AgI–CuI solid solutions

The ionic conductivity of the silver rich solid solutions Ag 1− x Cu x I (0< x<0.25) was measured using complex impedance spectroscopy over the frequency range 100 Hz–15 MHz and in the temperature range 25–250 °C. As observed in undoped AgI, two conducting regions (above and below T c) are found in these solid solutions also. Despite the large size difference in the ionic radii of Ag + and Cu + ions, the bigger sized Ag + ion dominates the overall conductivity of the system. Arrhenius plots of the dc conductivity demonstrates clearly the enhanced defect concentration and grain boundary effects in the low temperature phase as well as the smallness of the observed activation energy along with the softening of the AgI lattice in the high temperature phase. The pertinent effect of Cu doping in AgI is discussed in terms of the recent experimental and theoretical facts. A plausible conduction mechanism is being worked out.

Effect of Cu substitution on structure and magnetic properties of anisotropic SmCo ribbons

Anisotropic SmCo 7− x Cu x ( x=0–4.5) ribbons have been prepared by melt spinning at a low wheel speed of 5 m/s. Scanning electron microscopy results show that Cu-free and Cu-containing ribbons consist of equiaxed and columnar dendrite grains, respectively. The arrangement of columnar dendrite grains of the ribbons was found to be more ordered with increasing Cu content x. Together with the results of magnetic measurement, it is derived that Cu substitution is helpful to enhance the degree of preferred orientation of the c-axis of the columnar dendrite grains parallel to the longitudinal direction of the ribbons. In this way the rectangularity of demagnetization curves and the remanence ratio (defined as the ratio of remanent magnetization to saturation magnetization) of the samples are significantly improved. A remanence ratio of 0.90, which is close to that of sintered SmCo magnets, has been achieved in the ribbons with x=2.5. Because the domain-wall-energy gradient between the 1:5 and 2:17 phases, which determines the value of the coercive force arising from the domain wall pinning, may increase with x, the coercivity of the samples with x≤3.5 increases strongly with x. Without heat treatment, a coercive force ( i H c) of up to 9.2 kOe is obtained in the ribbons with x=3.5.

The effect of Cu substitution on the microstructure and magnetic properties of MnFe2O4 ferrite

The effect of compositional variation on grain size and porosity of Mn1 − xCu x Fe2O4 ferrite, where x = 0.0, 0.25, 0.50, 0.75, 1.00, prepared by standard ceramic method are reported. From microstructure analysis it follows that porosity increases with the Cu concentration where as coercivity increases up to x = 0.50. Above x = 0.5 the decrease in coercivity is explained on the basis of Neel's mathematical model treating the demagnetizing influence of non-magnetic material in cubic crystals. The coercivity, varies inversely with the grain size upto x = 0.5. The decrease in coercivity above x = 0.5 with grain size can be correlated with the inter-granular domain wall movement because of large porosity.

Synthesis of Cu-modified Co 2Z hexaferrite with planar structure by a citrate precursor method

Co 2Z hexaferrite is a planar anisotropic iron oxide which can present high values of permeability at high frequency. In this paper, Cu-modified Co 2Z hexaferrites powders were synthesized at a low temperature using a citrate precursor method. The formation of Z-type phases was characterized by X-ray diffraction and magnetization measurements. It is found that phase formation temperature and sintering temperature were influenced directly by the content of copper. The effects of Cu-substitution on the microstructure and high frequency properties of the ceramics have been investigated.

Low temperature sintering of MgCuZn ferrite and its electrical and magnetic properties

The low temperature sintering of MgCuZn ferrite was investigated using the usual ceramic method. The effect of Cu substitution on the properties of MgZn ferrites was also investigated and it was found that the densification of MgCuZn ferrite is dependent upon Cu concentration. The sintered ferrite with a density of 4.93 g/cm3 and electrical resistivity > 1011 Ω-cm was obtained for the ferrite with 12 mol% Cu at relatively low sintering temperature (910° C). The magnetic properties of the ferrites also improved by the Cu substitution. The chip inductors made of the ferrite fired at 910 C with 12 mol% Cu exhibited higher d.c. resistance. From these studies it is concluded that the good quality chip inductor can be obtained using the MgCuZn ferrites.

Driving force for adatom electromigration within mixed Cu/Al overlayers on Al(111)

A multiple scattering theory is used to study the effect of the addition of Cu upon the driving force for the electromigration of Al adatoms on an Al(111) surface. The theory employs a computational framework that combines a layer-Korringa Kohn–Rostoker calculation with the coherent potential approximation to describe the carrier scattering by a compositionally disordered overlayer. We investigate how the substitution of Cu for Al adatoms in the disordered overlayer alters the average effective wind valence of the Al and Cu adatoms within the overlayer. For adatom coverages smaller than approximately 0.2, we find that the effect of Cu substitution is to reduce the magnitude average effective wind valence of the Al adatoms by approximately +0.4%(Cu)−1 at 273 K.

Doping states and irreversibility fields of high-pressure-synthesized (Tl,Cu)Sr 2Ca 2Cu 3O y superconductors

The effects of Cu substitution for Tl in TlSr 2Ca 2Cu 3O y superconductor were investigated. Nearly single-phase samples of Tl 1− x Cu x Sr 2Ca 2Cu 3O y ( x=0.2−0.6) were successfully synthesized using a high pressure technique. The observed shrinkage in the lattice parameter a, concave ρ– T curve above T c and negative thermoelectric power near room temperature indicated that the Cu-substituted samples were over-doped. T c for the sample with x=0.4 increased from 73 to 94 K after annealing treatment in flowing argon gas. The Cu-substituted samples showed lower irreversibility field B irr as a function of reduced temperature than that of the pristine TlSr 2Ca 2Cu 3O y [Physica C 324 (1999) 15].

Dielectric behavior and DC resistivity of Ba3Co2(1−X)Cu2XFe24O41 (Co2Z)Hexaferrite

A series of Z-type hexaferrite samples of Ba3Co2(1−x)Cu2xFe24-δO41 with (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5) were prepared by the solid state reaction method at relatively low temperatures(between 1100–1150°C). The effect of Cu substitution on the electrical properties of Co2Z hexaferrite is investigated. Results show that the dielectric constant and dielectric loss tangent greatly degrade, dielectric relaxation peak shifts toward high frequency region, and DC resistivity increases. It's suggested that Cu substitution acts to reduce the electron hopping probability between Fe2+ and Fe3+.

Ionic conductivity in Cu-substituted Ag 3SBr

Nominally pure polycrystalline samples of Ag 3− x Cu x SBr in the composition range x=0→0.25 were prepared from the melt and annealed at 473 K for 6 months. For the x=0 compound, faint traces of unreacted AgBr can be detected by X-ray diffraction. As composition parameter x increases in the Cu-substituted samples, the cubic structure of Ag 3SBr is gradually lost while the proportion of unreacted silver halide grows. We investigate the effect of Cu substitution on the ionic conductivity of Ag 3SBr. With only small quantities of Cu replacing Ag in this compound, one observes a large reduction in the magnitude of the first-order conductivity change associated with the β–γ phase transition at 126 K. Furthermore, the activation energy governing Ag migration is increased in both the high-temperature β phase and the low-temperature γ phase with increasing Cu substitution.

Beneficial effects of Cu substitution on the microstructures and magnetic properties of Pr 2(FeCo) 14B/α-(FeCo) nanocomposites

We studied the phase composition, microstructures and magnetic properties of melt-spun Pr 8.5(Fe 0.8Co 0.2) 86.5− x Cu x B 5 ( x=0, 0.5, 1.0, 2.0, 3.0) nanocomposites. It was found that Cu addition suppresses the formation of Pr 2(CoFe) 17 phase and results in a two-phase mixture of α-(FeCo)/Pr 2(FeCo) 14B. Transmission electron microscopy (TEM) and energy-dispersive X-ray analysis (EDX) demonstrate that Cu strongly segregates at intergranular regions, leading to drastic decrease of the grain sizes of both 2:14:1 phase and α-(FeCo) phase. Wohlfarth remanence analysis indicates that the impact of Cu addition on the strength of exchange coupling interactions between hard and soft magnetic phases in the ribbons is determined by two opposite factors: (1) grain refinement and (2) grain isolation especially at higher Cu content. A small amount of Cu addition ( x=0–3.0) has little effect on the Curie temperature of 2:14:1 phase. The magnetic properties of B r, i H c, and ( BH) max of optimally processed Pr 8 5(Fe 0 8Co 0.2) 86.5− x Cu x B 5 ribbons initially increase with increasing Cu content from x=0 to 0.5 but all of them decrease drastically with further increasing Cu content, which can be mainly attributed to the variation of exchange coupling effect between hard and soft magnetic grains and the decrease in saturation magnetization. A combination of i H c=7.4 kOe, B r=10.9 kG and ( BH) max=20.1 MGOe has been obtained in Pr 8.5(Fe 0.8Co 0.2) 86Cu 0.5B 5 ribbon. Moreover, minor addition of Cu ( x=0.5) is effective in reducing the irreversible loss of induction ( h irr) of the studied Pr 2(FeCo) 14B/α-(FeCo) nanocomposite magnets.