Electrons In Cu Research Articles

First Principles Investigations on the Electronic and Magnetic Properties of La4Ba2Cu2O10

<p>Electronic and magnetic properties of La<sub>4</sub>Ba<sub>2</sub>Cu<sub>2</sub>O<sub>10</sub> had been studied by first-principles density functional theory (DFT). Based on the DFT calculation La<sub>4</sub>Ba<sub>2</sub>Cu<sub>2</sub>O<sub>10</sub> is found to have a ferromagnetic (FM) ground state. The material undergo charge-transfer type insulator to Mott-Hubbard type insulator transition which happens due to strong correlation in La-4f and Cu-3d states. Our results show that the 3d electrons of Cu hybridize strongly with O-2p states near the Fermi level giving rise to the insulating state of La<sub>4</sub>Ba<sub>2</sub>Cu<sub>2</sub>O<sub>10</sub>. Our study suggests that the enhanced magnetic moment is a result of itinerant exchange rather than the exchange interaction involving individual ions of Cu atoms. The total magnetic moment calculated in the present studies is 2 μ<sub>B</sub> per unit cell for La<sub>4</sub>Ba<sub>2</sub>Cu<sub>2</sub>O<sub>10</sub>.</p><p>Journal of Nepal Physical Society Vol.3(1) 2015: 89-96</p>

Angle resolved photoemission from Cu single crystals: Known facts and a few surprises about the photoemission process

We present angle resolved photoemission spectra for Cu(100) and Cu(111) singly crystals in normal emission geometry, taken at tightly spaced intervals for photon energies between 8eV and 150eV. This systematic collection of spectra gives unprecedented insight into the influence of the final states to the photoemission process as well as the band structure and lifetimes of highly excited electrons in Cu.

Preparation, structural, photoluminescence and magnetic studies of Cu doped ZnO nanoparticles co-doped with Ni by sol–gel method

Zn0.96−xNi0.04CuxO nanoparticles have been synthesized by varying different Cu concentrations between 0% and 4% using simple sol–gel method. X-ray diffraction studies confirmed the hexagonal structure of the prepared samples. The formation of secondary phases, CuO (111) and Zn (101) at higher Cu content is due un-reacted Cu2+ and Zn2+ ions present in the solution which reduces the interaction between precursor ions and surfaces of ZnO. Well agglomerated and rod-like structure noticed at Cu=4% greatly de-generate and enhanced the particle size. The nominal elemental composition of Zn, Cu, Ni and O was confirmed by energy dispersive X-ray analysis. Even though energy gap was increased (blue-shift) from Cu=0–2% by quantum size effect, the s–d and p–d exchange interactions between the band electrons of ZnO and localized d electrons of Cu and Ni led to decrease (red-shift) the energy gap at Cu=4%. Presence of Zn–Ni–Cu–O bond was confirmed by Fourier transform infrared analysis. Ultraviolet emission by band to band electronic transition and defect related blue emission were discussed by photoluminescence spectra. The observed optical properties concluded that the doping of Cu in the present system is useful to tune the emission wavelength and hence acting as the important candidates for the optoelectronic device applications. Ferromagnetic ordering of Cu=2% sample was enhanced by charge carrier concentration where as the antiferromagnetic interaction between neighboring Cu–Cu ions suppressed the ferromagnetism at higher doping concentrations of Cu.

Adsorption of CO and O2 on AumCun clusters: First principles calculations

The adsorption of CO and O2 molecules on Aun (n=2–5), Cun(n=2–5), and AumCun (m=1, 2, 3; 1≤n≤6) clusters is investigated in the framework of density functional theory. The equilibrium atomic geometry and electronic structure of each cluster are determined. It is found that Aun (n=2–5) clusters show strong reactivity toward CO, while they do not bind to molecular oxygen. High adsorption energy values can be obtained for odd number of Cun clusters for both CO and O2 adsorptions. Cu top site is energetically preferred for the adsorption of both CO and O2 molecules in AumCun clusters. The results of electronic density of states show an sp hybridization between Cu and O atoms in O2 adsorbed AumCun clusters. This interaction plays a major role in their binding. The highest occupied molecular orbital and the lowest unoccupied molecular orbital energy gap values and charge density differences are presented. There are charge transfers from s and d orbital electrons of Cu to p orbitals of C and of O atoms. It is observed that O2 adsorption on some clusters can induce half metallicity which is an ideal property for possible applications in spintronics.

Kerr rotation in Cu, Ag, and Au driven by spin accumulation and spin-orbit coupling

We measure transient spin accumulation in Cu, Ag, and Au by time-resolved magneto-optical Kerr effect. The transient spin current is generated by ultrafast demagnetization of a ferromagnetic [Co/Pt] layer, and spin accumulates in an adjacent normal metal, Cu, Ag, or Au by spin diffusion. The magnitude of the Kerr rotation is described by an off-diagonal conductivity tensor that is proportional to spin accumulation and spin-orbit coupling. From comparisons between observed Kerr rotations and calculated spin accumulations, we determine the strength of spin-orbit coupling of conduction electrons in Cu, Ag, and Au to be 0.02, 0.01, and $0.12\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$, respectively.

Formation of Cu precipitates in a high-energy-particle-irradiated and thermally aged Fe-0.6%Cu alloy

The stability of Cu precipitates in thermally aged Fe-Cu alloys after high-energy particle irradiation was investigated using a mono-energetic positron beam apparatus. The S-parameters did not change with increasing incident positron energy above 15 keV, which means positron annihilation at the surface does not influence the Doppler broadening (DB) spectra. In a non-aged sample, the S-parameter increased, while the W-parameter did not change upon ion irradiation at above 10 keV. By contrast, in the thermally aged sample, the S-parameter increased, while the W-parameter decreased upon ion irradiation. The DB spectra of thermally aged and non-aged samples have nealy the same shape after high-energy particle irradiation. In both thermally aged and non-aged samples, almost all positrons annihilate with electrons in Cu, and vacancy clusters covered with Cu atoms are formed upon neutron irradiation. This agrees with the results of previous studies. However, the defect growth process may be different in aged and non-aged samples.

Electronic and geometric structure of AuxCuy clusters studied by density functional theory

We have determined the stable structures of Au Cu n, Au 2 Cu n, Au 3 Cu n and Au x Cu 8-x clusters. It has been observed that Au Cu n, Au 2 Cu n and Au 3 Cu n systems have two-dimensional (2D) structures up to six atoms and they become three-dimensional (3D) afterwards. Au x Cu 8-x clusters favor 3D structures till the Au 7 Cu 1 cluster. We have found a lowest energy isomer of Au 6 Cu 2 from the literature. Bond lengths, binding energies, density of states (DOS), highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO-LUMO) gaps, ionization potential (IP) and electron affinity (EA) have been calculated for these structures using the first principles density functional theory (DFT) within the generalized gradient approximation (GGA) and the local density approximation (LDA). Generally, we have observed the overlap between s electrons of Cu and p electrons of Au near the Fermi level. Charge transfers are calculated by using the Löwdin analysis. It is observed that one Cu atom does not significantly modify the clusters which have more gold atoms. It is also seen that these clusters generally have nonmagnetic properties and results are consistent with the hybridization between s and d orbitals of Au in Au x Cu 8-x clusters.

A-Site-Ordered Perovskite MnCu3V4O12 with a 12-Coordinated Manganese(II)

A novel cubic perovskite MnCu3V4O12 has been synthesized at a high pressure and high temperature of 12 GPa and 1373 K. This compound crystallizes in the A-site-ordered perovskite structure (space group Im3) with lattice constant a = 7.26684(10) Å at room temperature. The most notable feature of this compound lies in the fact that the Mn(2+) ion is surrounded by 12 equidistant oxide ions to form a regular icosahedron; the situation of Mn(2+) is unprecedented for the crystal chemistry of an oxide. An anomalously large atomic displacement parameter U(iso)= 0.0222(8) Å(2) is found for Mn(2+) at room temperature, indicating that the thermal oscillation of the small Mn(2+) ion in a large icosahedron is fairly active. Magnetic susceptibility and electric resistivity measurements reveal that 3d electrons of Mn(2+) ions are mainly localized, while 3d electrons in Cu(2+) and V(4+) ions are delocalized and contribute to the metallic conduction.

K-shell ionization and radiative electron capture in 0.75–2.5 MeV u−1 32S, 35Cl + Cu atomic collisions

From the measured target thickness dependence of the K x-ray and radiative electron capture (REC) yields in the 0.75–2.5 MeV u−1 32S, 35Cl + Cu collisions, the cross sections for K x-ray production and REC, in dependence on collision energy, have been determined. In comparison with theory, we find simple models that describe rather well some of the present results. The target (Cu) K x-ray production cross sections are in fair agreement with ECPSSR model predictions. The REC theoretical calculations (Stobbe model times 11, the number of loosely bound electrons in Cu) are in agreement with the present data for Cl + Cu collision, but overestimate the data for S + Cu collision by approximately a factor of 2. Large enhancements for the projectile K-shell fluorescence yields, up to 10 for S and 6 for Cl, as well as for K-shell vacancy lifetimes, up to 16 for S and 21 for Cl, are reported.

Ab initio local energy and local stress: application to tilt and twist grain boundaries in Cu and Al

The energy-density and stress-density schemes (Shiihara et al 2010 Phys. Rev. B 81 075441) within the projector augmented wave (PAW) method based on the generalized gradient approximation (GGA) have been applied to tilt and twist grain boundaries (GBs) and single vacancies in Cu and Al. Local energy and local stress at GBs and defects are obtained by integrating the energy and stress densities in each local region by the Bader integration using a recent algorithm (Yu et al 2011 J. Chem. Phys. 134 064111) as well as by the layer-by-layer integration so as to settle the gauge-dependent problem in the kinetic terms. Results are compared with those by the fuzzy-Voronoi integration and by the embedded atom method (EAM). The features of local energy and local stress at GBs and vacancies depend on the bonding nature of each material. Valence electrons in Al mainly located in the interatomic regions show remarkable response to structural disorder as significant valence charge redistribution or bond reconstruction, often leading to long-range variations of charges, energies and stresses, quite differently from d electrons in Cu mainly located near nuclei. All these features can be well represented by our local energy and local stress. The EAM potential for Al does not reproduce correct local energy or local stress, while the EAM potential for Cu provides satisfactory results.

Synthesis, characterization, and solid state electrical conductivity of coordination polymers with copper and zinc

Heterobimetallic complexes [Cu x Zn1− x (dadb) · yH2O] n {where dadb = 2,5-diamino-3,6-dichloro-1,4-benzoquinone (1); x = 1 (2), 0.5 (4), 0.25 (5), 0.125 (6), 0.0625 (7), and 0 (3); y = 2; n = degree of polymerization} were synthesized and characterized. All metal complexes are stable at room temperature but weakly absorb moisture on exposure to air. Monometallic 2 exhibits subnormal magnetic moment whereas 3 exhibits diamagnetism. Heterobimetallic complexes exhibit normal magnetic moments. Heterobimetallic complexes are characterized from powder X-ray diffraction, thermal analysis, and electron spin resonance (ESR) spectral studies. Delocalization of unpaired electron from metal to ligand has been inferred from ESR and natural bond orbital (NBO) analysis. Greater delocalization of unpaired electron of Cu(II) on ligand of 4 as compared to that of 2 is reflected from NBO analysis. Heterobimetallic complexes show higher conductivity than monometallic complexes; all the complexes exhibit semiconductor behavior.

Visible-Light Responsive Photocatalytic Fuel Cell Based on WO3/W Photoanode and Cu2O/Cu Photocathode for Simultaneous Wastewater Treatment and Electricity Generation

A visible-light driven photocatalytic fuel cell (PFC) system comprised of WO(3)/W photoanode and Cu(2)O/Cu photocathode was established for organic compounds degradation with simultaneous electricity generation. The central idea for its operation is the mismatched Fermi levels between the two photoelectrodes. Under light illumination, the Fermi level of WO(3)/W photoanode is higher than that of Cu(2)O/Cu photocathode. An interior bias can be produced based on which the electrons of WO(3)/W photoanode can transfer from the external circuit to combine with the holes of Cu(2)O/Cu photocathode then generates the electricity. In this manner, the electron/hole pairs separations at two photoelectrodes are facilitated to release the holes of WO(3)/W photoanode and electrons of Cu(2)O/Cu photocathode. Organic compounds can be decomposed by the holes of WO(3)/W photoanode due to its high oxidation power (+3.1-3.2 V(NHE)). The results demonstrated that various model compounds including phenol, Rhodamine B, and Congo red can be successfully decomposed in this PFC system, with the degradation rate after 5 h operation were obtained to be 58%, 63%, and 74%, respectively. The consistent operation for continuous water treatment with the electricity generation at a long time scale was also confirmed from the result. The proposed PFC system provides a self-sustained and energy-saving way for simultaneous wastewater treatment and energy recovery.

FIRST-PRINCIPLE STUDY ON STRUCTURAL, ELASTIC AND ELECTRONIC PROPERTIES OF BINARY RARE EARTH INTERMETALLIC COMPOUNDS: GdCu AND GdZn

First principle study on structural, elastic and electronic properties of binary copper and zinc based rare earth intermetallics have been carried out using the full-potential augmented plane waves plus local orbital (APW+ lo) within density functional theory (DFT). Results on elastic properties are obtained using generalized gradient approximation (GGA) for exchange correlation potentials. The equilibrium lattice parameter, bulk modulus and its pressure derivative have been obtained using optimization method. Young's modulus, shear modulus, Poisson ratio, sound velocities for longitudinal and shear waves, Debye average velocity, Debye temperature and Grüneisen parameters have been calculated. From electronic calculations, it has been found that electronic conduction in copper and zinc based rare earth intermetallics is mainly attributed to 3d-orbital electrons of Cu and Zn .

高温超電導材料Ⅰ

As the first lecture of the series on high-temperature superconducting materials, this article provides a basic introduction so that non-specialists can catch up with current topics and understand some details about the copper oxides which show high-Tc superconductivity. The crystal structure and the electronic properties of the cuprates are described as a function of carrier doping. Many investigators have recognized that the anisotropic Cooper pairs with d x2-y2-symmetry are formed in the two-dimensional CuO2 planes. Some proposals, which may lead to the basic pairing mechanism for the superconductivity in the cuprates, are discussed. The most likely scenarios have been proposed based on both antiferromagnetic interaction and strong correlation between 3d electrons of Cu. Some trials to improve Tc are reviewed with an optimistic objective achieving room-temperature superconductors.

First-principle study on structural, elastic and electronic properties of rare-earth intermetallic compounds: TbCu and TbZn

Structural, elastic and electronic properties of TbCu and TbZn have been studied using the full-potential augmented plane waves plus local orbital (APW+lo) within density functional theory (DFT). Results on elastic properties are obtained using both the local density approximation (LDA) and generalized gradient approximation (GGA) for exchange correlation potentials. The equilibrium lattice parameter, bulk modulus and its pressure derivative have been obtained using optimization method. Young’s modulus, shear modulus, Poisson ratio, sound velocities for longitudinal and shear waves, Debye average velocity, Debye temperature and Grüneisen parameters have been calculated. Taking elastic moduli (calculated from first-principle approach) as reference values at 0K, temperature variation of elastic moduli has also been calculated using electrostatic and Born repulsive potentials and taking interactions up to next nearest neighbours. Calculated structural, elastic and other parameters are consistent with available data. From electronic calculations, it has been found that electronic conductivity in TbCu and TbZn is attributed to 3d-orbital electrons of Cu and Zn.

Dicarboxylate assisted synthesis of the monoclinic heterometallic tetrathiocyanato bridged copper(II) and mercury(II) coordination polymer {Cu[Hg(SCN) 4]} n: Synthesis, structural, vibration, luminescence, EPR studies and DFT calculations

The synthesis of the monoclinic polymorph of {Cu[Hg(SCN) 4]} n is reported. The compound, as determined by X-ray diffraction of a twinned crystal, consists of mercury and copper atoms linked by μ 1,3-SCN bridges. The crystal packing shows a highly porous infinite 3D structure. Diagnostic resonances for the SCN – ligand and metal–ligand bonds in the IR, far-IR and Raman spectra are assigned and discussed. The electronic band structure along with density of states (DOS) calculated by the DFT method indicates that the compound is an indirect band gap semiconductor. The DFT calculations show that the observed luminescence of the compound arises mainly from an excited LLCT state with small MLCT contributions (from the copper to unoccupied π ⁎ orbital of the thiocyanate groups). The X-band EPR spectrum of the powdered sample at room temperature reveals an axial signal with anisotropic g factors consistent with the unpaired electron of Cu(II) ion in the d x 2 − y 2 orbital.

ZnO-based visible-light photocatalyst: Band-gap engineering and multi-electron reduction by co-catalyst

Efficient ZnO based visible-light photocatalysts, Cu(II) modified CdxZn1−xO were developed by adopting a hybrid approach, consisting of band-engineering by formation of a solid solution and surface modification of co-catalysts. The CdxZn1−xO solid solution exhibited the visible-light activity for decomposing gaseous acetaldehyde, while bare ZnO showed negligible activity under visible-light. Further, the visible-light activity of CdxZn1−xO photocatalysts was greatly improved by the surface modification of Cu2+ ions. Photogenerated electrons in CdxZn1−xO are injected into the modified Cu2+ ions under visible-light irradiation, and electrons in Cu2+/Cu+ redox couples cause the efficient reduction of absorbed oxygen molecules. The strategy in the present study is a promising approach for applying ZnO-based photocatalysts for indoor applications.

Photoinduced charge transfer in ZnO/Cu2O heterostructure films studied by surface photovoltage technique

ZnO/Cu(2)O heterostructure films were prepared by a two-step electrodeposition method in aqueous solution on fluorine-doped tin oxide (FTO) substrates. Scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and UV-vis transmission measurements were utilized to characterize the films. Surface photovoltage (SPV) technique was used to investigate the process of photoinduced charge transfer. The results show that there is an electric field located at the interface between ZnO and Cu(2)O film and the photoinduced electrons in Cu(2)O film inject into ZnO under the effect of interfacial electric field with visible light irradiation. While under ultraviolet light illumination, the photoinduced electrons in Cu(2)O film accumulate at the surface of Cu(2)O film instead of injecting into ZnO under the action of surface built-in electric field of Cu(2)O film. The work function measurements confirm that the direction of interfacial electric field is from ZnO to Cu(2)O. These results are help to future design of high performance heterostructure photovoltaic devices.

Simultaneously optimizing the interdependent thermoelectric parameters inCe(Ni1−xCux)2Al3

Substitution of Cu for Ni in the Kondo lattice system CeNi$_2$Al$_3$ results in a simultaneous optimization of the three interdependent thermoelectric parameters: thermoelectric power, electrical and thermal conductivities, where the electronic change in conduction band induced by the extra electron of Cu is shown to be crucial. The obtained thermoelectric figure of merit $zT$ amounts to 0.125 at around 100 K, comparable to the best values known for Kondo compounds. The realization of ideal thermoelectric optimization in Ce(Ni$_{1-x}$Cu$_x$)$_2$Al$_3$ indicates that proper electronic tuning of Kondo compounds is a promising approach to efficient thermoelectric materials for cryogenic application.

Simulation of secondary electron emission spectra from thin metal foils after proton impact

We have derived inelastic interaction cross sections for electrons and protons with Al, Cu, and Au within the framework of a plane-wave Born approximation and an optical data model. We have implemented a transport model for protons and electrons in Cu into the Monte Carlo track structure code PARTRAC. We have simulated secondary electron yields in Cu and compared them with measurements from the literature. We find that simulated yields in general follow the measurements but clearly overestimate them at energies below 50 eV.