Electrons In Cu Research Articles

Cu@CuOx/WO3 with photo-regulated singlet oxygen and oxygen adatoms generation for selective photocatalytic aromatic amines to imines

Photocatalysts can absorb light and activate molecular O2 under mild conditions, but the generation of unsuitable reactive oxygen species often limits their use in synthesizing fine chemicals. To address this issue, we disperse 1 wt% copper on tungsten trioxide (WO3) support to create an efficient catalyst for selective oxidative coupling of aromatic amines to imines under sunlight irradiation at room temperature. Copper consists of a metallic copper core and an oxide shell. Experimental and density functional theory calculations have confirmed that Cu2O is the primary activation site. Under λ < 475 nm, the light excites electrons of the valence bands in Cu2O and WO3, which activate O2 to superoxide radical •O2−. Then rapidly transforms into oxygen adatoms (•O) and oxygen anion radicals (•O−) species on the surface of Cu2O. Simultaneously, it is captured by holes in the WO3 valence band to generate singlet oxygen (1O2). •O bind to 1O2 promoting the coupling reaction of amines. When λ > 475 nm, intense light absorption due to the localized surface plasmon resonance excites numerous electrons in Cu to promote the oxidative coupling with the adsorbed O2. This study presents a promising approach towards the design of high-performance photocatalysts for solar energy conversion and environmentally-friendly oxidative organic synthesis.

First-principles study of stability and electronic structural properties of Ag/Au/M (Cu, Ni) interface

This study investigated the interface energy, work of adhesion, and electronic structural properties at the Ag/Au/M(Cu,Ni) interface, employing the first-principles method based on density functional theory. First, the structures of various binary and ternary interfaces were optimized. Subsequently, the total density of states (TDOS), partial density of states (PDOS), charge distribution, and bonding characteristics of these interfaces were investigated. Additionally, the interface energy and work of adhesion of these interfaces were calculated. The results indicated that the Ag/Au/Ni interface exhibited higher stability and bonding strength compared to the Ag/Au/Cu interface. The contribution of the PDOS of atoms at the Ag/Au/M(Cu,Ni) interface to the TDOS can be primarily attributed to d-orbital electrons, while s- and p-orbit electrons had minimal influence on PDOS.Notably, d-d orbital hybridization emerged between the d-orbit electrons in Cu and Ni atoms and those in Ag and Au atoms, enhancing structural stability. Two distinct peaks in the TDOS of Ag/Ni, Au/Ni, and Ag/Au/Ni interfaces appeared near the Fermi level, corresponding to d-d orbital hybridization involving Ni, Ag, and Au atoms. At the Ag/Au/Cu and Ag/Au/Ni interfaces, resonance peaks corresponding to the s and p orbits of Ag and the s and p orbits of Au, as well as the d orbits of Ag and Au, indicated the presence of a relatively strong metallic bond between Ag and Au atoms. Furthermore, the Ag/Ni and Au/Ni systems exhibited greater average electron transfer compared to the Ag/Cu and Au/Cu systems. Moreover, atomic bond lengths at the Ag/Au/Ni interface were significantly less than those at the Ag/Au/Cu interface, indicating higher stability of the Ag/Au/Ni interface compared to the Ag/Au/Cu interface.

Structures and colossal dielectric behavior of Na1/3Ca1/3La1/3Cu3Ti4O12 ceramics fabricated via a sol−gel process

The dielectric response of a novel giant dielectric ceramic with good dielectric and electrical properties, Na1/3Ca1/3La1/3Cu3Ti4O12, was investigated in this work. This ceramic, with a perovskite−like structure, was successfully synthesized using a sol−gel method. Fine-grain ceramics were found in all sintered specimens. These ceramics produced large dielectric permittivities, 9.89 × 103−1.04 × 104, and low dielectric loss tangent values of 0.040–0.057. First-principles calculations indicated that Na+ is substituted at the Cu2+ sites. Additionally, La3+ likely occupies Ca2+ sites. Experimental and computational techniques demonstrated the presence of an oxygen vacancy in the Na1/3Ca1/3La1/3Cu3Ti4O12 lattice that results in generation of Cu+ and Ti3+. The IBLC phenomenon and small polaron hopping between valence electrons of Cu and Ti ions have been recognized as the causes of the giant dielectric behavior of these materials.

Spin-Enhanced C–C Coupling in CO 2 Electroreduction with Oxide-Derived Copper

Spin-Enhanced C–C Coupling in CO ₂ Electroreduction with Oxide-Derived Copper

Orientation independent heat transport characteristics of diamond/copper interface with ion beam bombardment

Owing to high thermal conductivity (k) and appropriate coefficient of thermal expansion (CTE), Diamond/copper (Dia/Cu) composites have attracted extensive attention as advanced thermal management materials, but also suffered with low thermal boundary conductance (G). This is because complex energy carrier behaviors at metal/nonmetal interfaces. Although conventional carbide forming interlayers may serve as acoustic matching bridge, crystallographic orientation is still critical to influence heat transport characteristics of Dia/Cu interface. In this work, both theoretical calculations and time-domain thermoreflectance (TDTR) results revealed two distinct G of (100) and (111) Dia/Cu interfaces. We then applied an easy-controlled ion-beam bombardment technique to reduce the orientation dependent G, and two different trends are observed with ion-bombardment time (t): (1) when t < 30 min, G increases with increasing t; (2) when t > 30 min, G decreases with increasing t. Our microstructural and surface potential analysis suggests sp3-to-sp2 hybridization and formation of nanoscale amorphous carbon (a–C) layer at the diamond surface. The coupling between electrons in Cu and a–C provides an additional heat transport pathway, however, the interfacial defect scattering becomes dominant when continuously increasing ion-bombardment time. The present findings may provide more insight to understand the orientation dependent heat transport mechanisms at metal/nonmetal interfaces.

Identification of Auger mechanisms responsible for low energy electron emission from graphene on copper using Auger-gamma coincidence spectroscopy

We have applied positron annihilation induced Auger-gamma coincidence spectroscopy to identify important mechanisms responsible for the emission of low energy electrons following the sudden creation of holes in bilayer graphene on copper substrate. The novel surface spectroscopic method measures the energy of the Doppler shifted annihilation gamma photon in coincidence with the Auger electron emitted following the relaxation of the hole created by the annihilation of a surface electron with a surface trapped positron. By extracting and theoretically modelling the annihilation gamma spectra coincident with low energy electrons, we associate majority of the intensity in the low energy (7 eV–25 eV) region of the Auger spectrum to electron emission following Auger decays of 2s holes in adsorbed oxygen and deep valence holes in graphene. We provide additional support to this conclusion by showing that most of the Auger electrons with energy less than ∼ 25 eV are coincident with gamma photons with small Doppler shift (511 keV–512 keV) indicating that the primary electron whose annihilation resulted in low energy Auger electron emission had small momentum parallel to the gamma emission direction. On the other hand, majority of the Auger electrons measured in coincidence with the photons having maximum Doppler shift (515 keV–521 keV) were emitted following the decay of core holes (C 1s and O 1s). By selecting annihilation gamma photons coincident only with the O KVV (from surface adsorbed oxygen), C KVV (graphene), and Cu MVV (copper substrate) Auger electrons, we have also experimentally derived the energy spectrum of Doppler shifted gamma photons resulting from the annihilation of positrons with 1s electrons of O, 1s electrons of C and 3p electrons of Cu respectively. Model Doppler broadened gamma spectra produced using ab-initio calculations agree well with the experimentally derived line shapes. This demonstrates the ability of Auger-gamma coincidence method to experimentally resolve the Doppler broadened annihilation gamma spectrum from surfaces into its veiled electronic level constituents which has, heretofore, relied solely on theoretical analysis. Our results also demonstrate that the line shape of the Doppler broadened annihilation gamma peak reflect the chemical composition of the topmost atomic layer and can thus be used to characterize both external and inaccessible surfaces of porous materials.

Superb Nonlinear Absorption of Triphenylene‐Based Metal–Organic Frameworks Associated with Abundant Metal d Electrons

AbstractThe exploitation of high‐performance nonlinear optical (NLO) materials is necessitated by the broad application of ultra‐intensive and ultra‐fast lasers. The superb nonlinear absorption and electronic‐structure‐related NLO response of M3HHTP2 are introduced here, where M is Co(II), Ni(II), or Cu(II) and HHTP is 2,3,6,7,10,11‐hexahydroxytriphenylene. With the laser excitation at 532 nm, the Cu3HHTP2 exhibits a two‐photon absorption (2PA) cross‐section of 1.38 ± 0.11 × 107 GM, a value much larger than those of most reported NLO materials so far. The NLO response of M3HHTP2 correlates strongly with the number of metal d electrons. With metal d electrons number increasing from 7 to 10, the optical nonlinearity of M3HHTP2 under the laser excitation at 532 nm varies from three‐photon absorption (3PA) in Co3HHTP2, a combination of 3PA and 2PA in Ni3HHTP2, to 2PA in Cu3HHTP2. Abundant metal d electrons can mitigate the ground‐state depletion, and therefore the 2PA is enhanced. Accordingly, the superb nonlinear absorption of Cu3HHTP2 can be associated with abundant d electrons in Cu.

One-pot in situ fabrication of Cu-coupled rugby-shaped BiVO4 sosoloid for enhancing photocatalytic activity with SPR effect via ultrasonic hydrothermal strategy

One-pot wet chemistry strategy via an ultrasonic hydrothermal in situ procedure has been applied to construct a serial of monoclinic Cu-coupled rugby-shaped hierarchical BiVO4 sosoloids with diverse Cu coupling amount. The SEM and TEM images indicate that the coupled copper content had no effect on the crystalline phase of bismuth vanadate, but it had an important effect on its morphology, which changed from seed shape to rugby shape. As demonstrated by XRD and XPS analysis, it was found parts of Cu2+ doped into the BiVO4 monoclinic lattice to make it self-assemble into a rugby-shaped solid solution and another part of Cu loaded on the surface of BiVO4 sosoloids. Under visible light illumination (>420 nm), as-obtained 1.5% Cu-BiVO4 sosoloid had a degradation rate reached 99% for RhB within 50 min, and its photodegradation activity was 5.6 times higher than that of pure BiVO4. and remained above 96% after 5 cycles. The enhanced photocatalytic efficiency of xCu-BiVO4 sosoloids may be mainly attributed to the superior Cu-coupled rugby-shaped BiVO4 sosoloid microstructures with large specific surface area. During the ultrasonic hydrothermal process, the doping Cu2+ can effectively replace V5+ ions to form a virtual energy level accompanied by V4+, which can become a trapping center and capture the excitation electrons on the conduction band. The surface plasmon resonance (SPR) effect of copper can effectively expand the range of visible light response. On the other hand, d orbital electrons of Cu can quickly transfer to the BiVO4 conduction band according to Fermi energy level, so as to promote the interfacial charge transfer process, thus inhibiting the recombination of photo-generated carriers and improving the photocatalytic activity. Based on the synergetic effects of components in degradation of organic contaminants, this study provides a promising photocatalytic material driven by visible light for environmental remediation and protection.

Oxidation of Ethanol in Cu-Faujasites Studied by IR Spectroscopy

In this study, IR studies of the coadsorption of ethanol and CO on Cu+ cations evidenced the transfer of electrons from ethanol to Cu+, which caused the lowering of the frequency of the band attributed to CO bonded to the same Cu+ cation due to the more effective π back donation of d electrons of Cu to antibonding π* orbitals of CO. The reaction of ethanol with acid sites in zeolite HFAU above 370 K produced water and ethane, polymerizing to polyethylene. Ethanol adsorbed on zeolite Cu(2)HFAU containing acid sites and Cu+exch also produced ethene, but in this case, the ethene was bonded to Cu+ and did not polymerize. C=C stretching, which is IR non-active in the free ethene molecule, became IR active, and a weak IR band at 1538 cm−1 was present. The reaction of ethanol above 370 K in Cu(5)NaFAU zeolite (containing small amounts of Cu+exch and bigger amounts of Cu+ox, Cu2+exch and CuO) produced acetaldehyde, which was further oxidized to the acetate species (CH3COO−). As oxygen was not supplied, the donors of oxygen were the Cu species present in our zeolite. The CO and NO adsorption experiments performed in Cu-zeolite before and after ethanol reaction evidenced that both Cu+ox and Cu2+ (Cu2+exch and CuO) were consumed by the ethanol oxidation reaction. The studies of the considered reaction of bulk CuO and Cu2O as well as zeolites, in which the contribution of Cu+ox species was reduced by various treatments, suggest that ethanol was oxidized to acetaldehyde by Cu2+ox (the role of Cu+ox could not be elucidated), but Cu+ox was the oxygen donor in the acetate formation.

Theoretical Study of NO Dissociative Adsorption onto 3d Metal Particles M55 (M = Fe, Co, Ni, and Cu): Relation between the Reactivity and Position of the Metal Element in the Periodic Table.

NO dissociative adsorption onto 3d metal particles M55 (M = Fe, Co, Ni, and Cu) was investigated theoretically using density functional theory computations. A transition state exists at higher energy in the Cu case but at lower energy in the Fe, Co, and Ni cases than the reactant (sum of M55 and NO), indicating that Cu55 is not reactive for NO dissociative adsorption because NO desorption occurs more easily than the N–O bond cleavage in this case, but Fe55, Co55, and Ni55 are reactive because NO desorption needs a larger destabilization energy than the N–O bond cleavage. This result agrees with the experimental findings. The energy of transition state E(TS) becomes higher in the order of Fe < Co < Ni ≪ Cu. Exothermicity Eexo (relative energy to the reactant) decreases in the order of Fe > Co > Ni ≫ Cu. These results indicate that the reactivity for NO dissociative adsorption decreases kinetically and thermodynamically in this order. In addition, the E(TS) and Eexo values show that 3d metal particles are more reactive than 4d metal particles when a comparison is made in the same group of the periodic table. Charge transfer (CT) from the metal particle to NO increases as the reaction proceeds. The CT quantity to NO at the TS increases in the order of Cu < Ni < Co < Fe, identical to the increasing order of reactivity. The negative charges of the N and O atoms of the product (N and O adsorbed M55) increase in the order of Ni < Co < Cu < Fe, identical to the increasing order of Eexo except for the Cu case; in the Cu case, the discrepancy between the order of Eexo and those of the N and O negative charges arises from the presence of valence 4s electron of Cu because it suppresses the CT from N and O to Cu55. From these results, one can infer that the d-valence band-top energy of M55 plays an important role in determining the reactivity for NO dissociative adsorption. Truly, the d valence orbital energy decreases in the order of Fe > Co > Ni ≫ Cu and the 3d metal > 4d metal in the same group of the periodic table, which reflects the dependence of reactivity on the metal element position in the periodic table.

Hybrid functional analysis of porous coordination polymers Cu[Cu(pdt)2] and Cu[Ni(pdt)2

Ab initio investigation of the two porous coordination polymers Cu[Cu(pdt)$ _{2} $] and Cu[Ni(pdt)$ _{2} $] has been performed. The dispersion laws and partial density of states was obtained with the PBE0 hybrid functional. The results found here show that the materials under consideration are degenerate $p$-type semiconductors. Here, the effect of partial self-interaction removing of the strongly correlated 3$d$ electrons of Cu and Ni was examined. In case of Cu-containing materials, the obtained results confirm that the 3$d$ electrons of Cu reveal strong correlations, and, therefore, their electronic properties could be evaluated by means of a hybrid functional of the exchange-correlation energy. We also obtained quasiparticle properties within the Green's function (G0W0) and Bethe-Salpeter approaches. The last one was used in order to examine excitonic properties in the degenerate semiconductors. The imaginary part of the dielectric function was obtained within random-phase approximation as well as the Bethe-Salpeter approach.

Prediction of short range order in high-entropy alloys and its effect on the electronic, magnetic and mechanical properties

The prediction of stable state of high-entropy alloys (HEAs) is crucial to obtain fundamental insight to the excellent properties of HEAs. Taking a FeCuCrMnMo alloy as a case study, we combined Monte Carlo (MC) method with the density functional thoery (DFT) calculations (MC/DFT) to predict the equilibrium structure of high-entropy alloys in a finite unit cell. Instead of approaching the ideal random state obtained from special quasi-random approximation (SQS) method, physical factors such as atomic size, mixing enthalpy of atomic pairs, and interatomic interactions in the alloy are fully considered and implemented in our simulation by MC/DFT calculations. MC codes ensure the energy convergence of the system to the equilibrium state through the atom exchange process. The equilibrium structures exhibit Cu-rich short-range orders (SRO), which is consistent with the observation in experiments. Comparing with ideal random state structure, SRO structure is more stable in energy, and more closely packed in atomic arrangement. Moreover, the analyses of order parameters and radial distribution functions (RDFs) are performed to character the structure of high-entropy alloy. The order parameter of Cu-Cu atomic pair reaches to –0.53 in the SRO equilibrium structure, which indicates that Cu-rich regions appear in the alloy. The RDFs show that the atomic distance distribution of the SRO structure is between 2.25 Å to 2.7 Å, which is smaller than the range of 2.16 Å to 2.84 Å in the SQS structure, indicating that the lattice distortions is relatively small in the SRO structure after structural optimization. The appearing of SRO phenomena is attributed to the inherent characteristics of atoms, including (i) atomic size, (ii) interatomic mixing enthalpy and (iii) the interaction of atoms. Atomic sizes in the FeCuCrMnMo alloy are in the order of Fe (11.78) &lt; Cu (11.81) &lt; Cr (11.97) &lt; Mn (14.38) &lt; Mo (15.58), in unit of Å&lt;sup&gt;3&lt;/sup&gt;/atom. The relatively large sizes of Mn and Mo atoms should disadvantage the pairing of Mo-Mo and Mn-Mn. The mixing enthalpy of Cu with other atoms are all positive values, indicating that Cu is not favor of pairing other elements and precipitate itself. The analyses of density of state (DOS) and Crystal Orbital Hamilton Population (COHP) also support the results. The reason is exactly attributed to the inactive valence electrons of Cu. Furthermore, the effect of SRO on the magnetic and mechanical properties are investigated. The existence of SRO decreases the mean value of magnetic moment, and results in an increase of elastic moduli (&lt;i&gt;B&lt;/i&gt;, &lt;i&gt;G&lt;/i&gt; and &lt;i&gt;E&lt;/i&gt;) and a decrease in the ductility and anisotropy properties.

Contrasting roles of small metallic elements M (M = Cu, Zn, Ni) in enhancing the thermoelectric performance of n-type PbM0.01Se

The carrier concentration of PbCu0.01Se sample increases suddenly, which results from the release of 3d orbital electrons in Cu+ ions.

Aromatic SNF-Approach to Fluorinated Phenyl tert-Butyl Nitroxides.

The interaction of octafluorotoluene (1a), as well as pentafluorobenzonitrile (1b) with tert-butylamine, followed by the oxidation of thus formed tert-butylanilines (2a,b) with meta-chloroperoxybenzoic acid led to functionalized perfluorinated phenyl tert-butyl nitroxides [namely, 4-(N-tert-butyl(oxyl)amino)heptafluorotoluene (3a) and 4-(N-tert-butyl(oxyl)amino)tetrafluorobenzonitrile (3b)] with nearly quantitative total yields. The molecular and crystal structures of nitroxide 3a were proved by single crystal X-ray diffraction analysis. The radical nature of both nitroxides was confirmed by ESR data. The interaction of Cu(hfac)2 with the obtained nitroxides 3a,b gave corresponding trans-bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ2O,O′)bis{4-(N-tert-butyl(oxyl)amino)perfluoroarene-κO}copper (II) complexes ([Cu(hfac)2(3a)2] and [Cu(hfac)2(3b)2]). X-ray crystal structure analysis showed square bipyramid coordination of a centrally symmetric Cu polyhedron with the axial positions occupied by oxygen atoms of the nitroxide groups. Magnetic measurements revealed intramolecular ferromagnetic exchange interactions between unpaired electrons of Cu(II) ions and paramagnetic ligands, with exchange interaction parameters JCu–R reaching 53 cm−1.

Theoretical investigation on the electronic properties and UV–Vis absorption spectra of expanded porphyrin mono-Cu(II) complexes

The metalation chemistry of expanded porphyrins exhibits wide-ranging applications in numerous fields. In the work, we have investigated the electron spin density, charge transfer, frontier molecular orbitals and UV–Vis absorption spectra of four expanded porphyrin mono-Cu(II) complexes (Cu(II)@P, Cu(II)@HP, Cu(II)@OP and Cu(II)@d-OP) using density functional theory (DFT) method and time-dependent DFT. The results show that Cu(II)@HP has different electronic properties and absorption spectra compared with other complexes. What is more interesting is that the single electrons of Cu(II)@HP are not only distributed on the Cu atom and the four coordination N atoms, but also on the uncooridnation conjugated pyrroles. However, the single electrons of other complexes are mainly distributed on the Cu atom and the four coordination N atoms. This phenomenon can be successfully explained by the specific mechanism of Cu(II)@HP unlike the Zn(II)@HP. Meanwhile, the calculated values of extended charge decomposition analysis indicate that beta electrons of Cu(II)@HP have more transfer, and its frontier molecular orbitals demonstrate greater involvement of Cu(II) ion compared with other complexes. The particular properties give rise to the different absorption spectra of Cu(II)@HP. The maximum wavelength of Cu(II)@HP displays an unusual red-shift (over 100nm) compared with Cu(II)@d-OP. The absorption spectra of Cu(II)@HP can be assigned to π→π∗ transition and metal-to-ligand charge transfer characteristic. Emission wavelengths corresponding maximum absorption wavelengths of Cu(II)@HP is 610nm that show Stokes shift with 27nm. The aim of this work is to provide valuable information to contribute to synthesis of new metal complexes of expanded porphyrins and optical materials.

Experimental realization and characterization of an electronic Lieb lattice.

Geometry, whether on the atomic or nanoscale, is a key factor for the electronic band structure of materials. Some specific geometries give rise to novel and potentially useful electronic bands. For example, a honeycomb lattice leads to Dirac-type bands where the charge carriers behave as massless particles [1]. Theoretical predictions are triggering the exploration of novel 2D geometries [2–10], such as graphynes, Kagomé and the Lieb lattice. The latter is the 2D analogue of the 3D lattice exhibited by perovskites [2]; it is a square-depleted lattice, which is characterised by a band structure featuring Dirac cones intersected by a flat band. Whereas photonic and cold-atom Lieb lattices have been demonstrated [11–17], an electronic equivalent in 2D is difficult to realize in an existing material. Here, we report an electronic Lieb lattice formed by the surface state electrons of Cu(111) confined by an array of CO molecules positioned with a scanning tunneling microscope (STM). Using scanning tunneling microscopy, spectroscopy and wave-function mapping, we confirm the predicted characteristic electronic structure of the Lieb lattice. The experimental findings are corroborated by muffin-tin and tight-binding calculations. At higher energies, second-order electronic patterns are observed, which are equivalent to a super-Lieb lattice.

A first-principles study of the formation of θ′′ phase in Al–Cu alloys

The θ′′-Al3Cu phase plays an important role in the precipitation process of Al–Cu alloys. This phase has a sandwich structure—every two {200}Cu layers are separated by three {200}Al layers. To analyse the formation mechanism of this structure, the elastic strain energy of the {200}Cu and {200}Al layers, and the chemical bonding energy that reflects the interaction between the electrons in Cu and neighbouring Al atoms are calculated and analysed by first-principles calculations, projected density of states and Bader analysis. Our computation results reveal that this sandwich structure is energetically preferred in the competition of elastic strain and chemical bonding energies. To minimise the elastic strain energy of {200}Al and {200}Cu layers, the {200}Cu layers prefer being apart from each other, whereas the chemical bonding energy favours the opposite arrangement because the intermetallic bond between Al and Cu atoms may form through p-d hybridization.

Lifetime of excess electrons in Cu–Zn–Sn–Se powders

The method of time-resolved microwave photoconductivity at a frequency of 36 GHz in the range of temperatures of 200–300 K is used to study the kinetics of the annihilation of charge carriers in Cu–Zn–Sn–Se powders obtained by the solid-phase method of synthesis in cells. The lifetime of excess electrons at room temperature is found to be shorter than 5 ns. The activation energy for the process of recombination amounted to Ea ~ 0.054 eV.

Investigations on the origin of ferromagnetism of Cu doped anatase TiO2 nanotubes

The role of oxygen defects and dopants of Cu and N on ferromagnetism is discussed in undoped, N-doped, Cu-doped and Cu/N-codoped anatase TiO2 nanotube-arrays fabricated by two-step anodization method. X-ray photoelectron spectroscopy shows the presence of Cu2+ and/or Cu+ in the distorted octahedral coordination of TiO2. The UV–vis absorption spectra and photoluminescence spectra reveal the presence of oxygen defect related the peaks of absorption and emission in Cu-doped and Cu/N codoped-TiO2. Room temperature ferromagnetism is observed in all the TiO2 nanotubes. The saturation magnetizations for those specimens decreases in the order of Cu-doped, undoped, Cu/N-codoped and N-doped samples, which are in consistent with the results of the first-principles calculations based on density-functional theory. It is speculated that both oxygen vacancies and Cu d-states are involved in the ferromagnetism. Spin polarization occurs by the formation of bound magnetic polaron between electrons in Cu+/Cu2+ d-states and the unpaired spins in oxygen vacancies.

Cu0.02Ti0.94Nb2.04O7: An advanced anode material for lithium-ion batteries of electric vehicles

Abstract To explore advanced anode materials for lithium-ion batteries of electric vehicles, Cu 2+ /Nb 5+ co-doped TiNb 2 O 7 is studied. Cu 0.02 Ti 0.94 Nb 2.04 O 7 is successfully fabricated using a facile solid-state reaction. X-ray diffraction analyses combined with Rietveld refinements demonstrate that the trace Cu 2+ /Nb 5+ co-doping does not destroy the shear ReO 3 crystal structure of TiNb 2 O 7 but increases the lattice parameters and unit cell volume. Specific surface area tests and scanning electron microscopy images reveal a smaller average particle size in Cu 0.02 Ti 0.94 Nb 2.04 O 7 . Due to the increased unit cell volume and free 3d electrons in Cu 2+ ions, the Li + -ion diffusion coefficient and electronic conductivity of Cu 0.02 Ti 0.94 Nb 2.04 O 7 are respectively enhanced by 14.8 times and at least 220 times. Consequently, Cu 0.02 Ti 0.94 Nb 2.04 O 7 exhibits advanced electrochemical properties in terms of specific capacity, rate capability and cyclic stability. At 0.1 C, it delivers a large first-cycle discharge/charge capacity of 346/315 mAh g −1 . At 10 C, it still provides a large capacity of 182 mAh g −1 with tiny loss of only 1.2% over 1000 cycles. In sharp contrast, TiNb 2 O 7 shows a small capacity of only 90 mAh g −1 and large loss of 59.8%. Therefore, Cu 0.02 Ti 0.94 Nb 2.04 O 7 possesses great potential for the application in lithium-ion batteries for electric vehicles.