Vibrations Of Cu Research Articles

Lone Pair Induced 1D Character and Weak Cation-Anion Interactions: Two Ingredients for Low Thermal Conductivity in Mixed-Anion Metal Chalcohalide CuBiSCl2.

Mixed-anion compounds, which incorporate multiple types of anions into materials, display tailored crystal structures and physical/chemical properties, garnering immense interest in various applications such as batteries, catalysis, photovoltaics, and thermoelectrics. However, detailed studies regarding correlations among crystal structure, chemical bonding, and thermal/vibrational properties are rare for these compounds, which limits the exploration of mixed-anion compounds for associated thermal applications. In this work, we investigate the lattice dynamics and thermal transport properties of the metal chalcohalide, CuBiSCl2. A high-purity polycrystalline CuBiSCl2 sample exhibits a low lattice thermal conductivity (κL) of 0.9-0.6 W/(m·K) from 300 to 573 K. By combining various experimental techniques, including three-dimensional (3D) electron diffraction, with theoretical calculations, we elucidate the origin of low κL in CuBiSCl2. The stereochemical activity of the 6s2 lone pair of Bi3+ favors an asymmetric environment with neighboring anions involving both short and long bond lengths. This particularity often implies weak bonding, low structure dimensionality, and strong anharmonicity, leading to a low κL. In addition, the strong 2-fold linear S-Cu-S coordination with weak Cu···Cl interactions induces a large anisotropic vibration of Cu, which enables strong phonon-phonon scattering and decreases κL. The investigations into lattice dynamics and thermal transport properties of CuBiSCl2 broaden the scope of the existing mixed-anion compounds suitable for the associated thermal applications, offering a new avenue for the search for low thermal conductivity materials in low-cost mixed-anion compounds.

Morphology, physical, and structural aspects of copper nanoparticles induced- metal phosphate nanocompounds for gamma ray shielding and magnetic sensing applications

The inorganic nanocompounds were synthesized by solid state reaction with the composition 10Li2O+(30-x)Sb2O3 + xZnO + 59.5P2O5 + 0.5Cu (in mol%). SEM morphographs of the samples confirmed the grain size ≈0.5–2.5 μm. The EDAX spectra of the samples confirmed presence of copper (Cu) nanoparticles (<2 wt%) in the composition. The EDAX studies showed energy dispersion of Kα- photons by reactivity of elements P, Cu, and Zn, while the element Sb has shown dispersion of Lα- photons up to 10 keV. Mass attenuation coefficient (MAC) has exhibited a few discontinuities (bumps) at low energies (<10 keV) due to K, L- absorption edges of various elements (such as P, Cu, Zn, and Sb) presented in the samples. The shrinking of Phosphorous-Phosphorous separation (dP-P) from 4.716 Ao to 3.990 Ao indicated the greater solidity (or density) of the prepared nanocompounds at higher content of ZnO. XRD spectra showed the presence of major crystallites such as LiPO3, Li3PO4, Li6P6018, SbPO4, Cu3PO4, Cu2P2O7, Cu3[PO4]2, Zn[PO3]2, Zn2P2O7, ZnP4O11, and LiZnPO4 in the prepared nanocompounds. The average crystallite size was determined in the range of 35–83 nm. FTIR spectra of these compounds displayed the [PO2]−, [PO3]−, [PO4]3−, and [ZnO4] units along with linkages P─O─P, O─P─O, Sb─O─Sb, Cu─O─Cu, etc. A band due to vibrations of Cu─O bond has been observed in the range of 466–478 cm−1, which endorses the contribution of copper nanoparticles in the solid state reaction of the metal phosphate nanocompounds. A partially resolved hyperfine structure of magnetic resonance signals corresponding to g|| ≈2.4 and g⊥ ≈2.05 were observed due to the presence of an anisotropic hyperfine interaction of the electron spin (S = 1/2) with the nuclear spin (I = 3/2) of copper isotopes (63Cu and 65Cu) in the samples.

Local symmetry distortion induced anomalous thermal conduction in thermoelectric layered oxyselenides

Polyhedral distortion, associated closely with the atomic arrangement and interatomic interactions, drives many unique behaviors in solids, such as phase transition and negative thermal expansion. In thermoelectric heteroanionic oxides, the anionic polyhedra are widely present, but their effect on thermal transport is rarely investigated. Here, we report an anomalous thermal conduction induced by local symmetry distortion in layered oxyselenides via solving the Boltzmann transport equation based on first-principles calculations. We found interestingly that lighter BiCuSeO exhibits lower thermal conductivity than heavier BiAgSeO. Due to the different distorted degrees of CuSe4 and AgSe4 tetrahedrons, Cu prefers the in-plane vibration, while Ag has more tendency of out-of-plane vibration. Thus, the heat-carrying phonons dominated by the rattling-like vibration of Cu are significantly suppressed, resulting in lower thermal conductivity of BiCuSeO. This study highlights the importance of polyhedral distortion in regulating thermal conduction in layered heteroanionic materials.

Green synthesis of highly efficient and stable copper oxide nanoparticles using an aqueous seed extract of Moringa stenopetala for sunlight-assisted catalytic degradation of Congo red and alizarin red s

Environmental pollution by organic pollutants because of population growth and industrial expansion is a global concern. Following this, the fabrication of single and efficient nanomaterials for pollution control is highly demanded. Under this study, highly efficient and stable copper oxide nanoparticles (CuO NPs) were synthesized through the green method using Moringa stenopetala seed extract. XRD, UV–vis, FT-IR, and SEM were applied to characterize the synthesized material. From XRD data, the average particle size was found to be 6.556 nm, and the nanoparticles are crystalline in nature. The formation of CuO NPs was demonstrated by FT-IR spectra of Cu–O in different bending vibration bands at 535 cm-1 and 1122 cm-1, as well as stretching vibration of Cu–O at 1640 cm-1. From UV–visible spectroscopic measurements, the energy band gap of greenly synthesized CuO NPs was found to be 1.73 eV. The SEM result shows that the nanoparticles' surfaces are rough, with some of the particles having spherically random orientation. The photodegradation efficiency of green synthesized CuO NPs photocatalyst was found to be 98.35% for Congo red at optimum experimental parameters (initial concentration, 25 mg/L; exposure time, 120 min; catalyst dose, 0.2 g; and pH, 5) and 95.4% for Alizarin Red S at optimum experimental parameters (catalyst dose, 0.25 g; initial concentration, 40 mg/L; exposure time, 120 min; and pH, 4.6). The COD values determined for the degraded product strongly support the complete mineralization of the dyes toward nontoxic materials. Reusability of the catalyst was investigated for five cycles, and the results clearly indicate the green synthesized CuO NPs are highly stable, can be used for several times, and are cost-effective as well. The degradation of Congo red and Alizarin red S on the surface of the CuO NPs follows the MBG kinetic model.

Spin excitations coupled with lattice and charge dynamics in La2−xSrxCuO4

Spin excitations of layered copper oxide show various characteristic features, depending on the carrier concentration. In this study, we conducted inelastic neutron scattering (INS) measurements on La$_{2-x}$Sr$_{x}$CuO$_4$ (LSCO), with $x$ = 0, 0.075, 0.18, and 0.30 and La$_{2-x}$Sr$_{x}$NiO$_4$ (LSNO) with 1/3, to clarify the origin of the intensity enhancement in the excitation spectrum of LSCO at the energy ($\omega$) of 16--19 meV [Phys. Rev. B {\bf 91}, 224404 (2015), {\it ibid}. {\bf 93}, 094416 (2016)]. We confirmed the presence of a peak-structure in the $\omega$-dependence of the local spin susceptibility $\chi''(\omega)$ of superconducting (SC) LSCO with a peak energy of 16--19 meV, where the spin excitations intersect optical phonon branches. A comparable peak-structure is not observed in the insulating La$_2$CuO$_4$, LSNO, and heavily overdoped LSCO with $x$ = 0.30. A dome-shaped $x$-dependence of the integrated intensity around the peak energies is revealed for SC phase by summarizing the present and previously reported results. Furthermore, our phonon calculation on LCO shows the existence of two optical branches at $\sim$19 meV that could stabilize stripe-alignment of carriers due to out-of-plane vibrations of Cu or O of the CuO$_2$ planes. These results indicate the interplay among spin, charge, and lattice dynamics and suggest that the intensity enhancement is associated with their composite excitations.

Hydrothermal synthesis of CuO and CeO2/CuO nanostructures: spectroscopic and temperature dependent electrical properties

In this study, CuO and CeO2/CuO nanostructures were successfully synthesized via a hydrothermal route. The structure, morphology, composition and optical properties of these nanostructures have been studied using various techniques. X-ray diffraction (XRD) analysis showed the formation of monoclinic crystalline phase of CuO with a decrease in the crystallinity of the samples as the Ce content increased. Scanning electron microscopy (SEM) acquired images showing that increased Ce incorporation induces transformation of morphology from spherical to rod-like nanostructures. Energy-dispersive X-ray spectroscopy (EDS) mapping showed that Ce was homogeneously distributed onto the CuO matrix. UV/Vis/NIR spectrophotometer measurements depicted a blue shift in the bandgap from 2.0 to 3.5 eV for 0%-6% Ce and then 3.2 eV for 8% Ce. Brunauer Emmett Teller (BET) analysis revealed enhanced porosity with the incorporation of cerium. Raman spectroscopy results confirmed the presence of the $${A}_{g}$$ (296 cm−1), $${B}_{g}$$ (346 cm−1) and $${B}_{g}$$ (631 cm−1) modes belonging to CuO. The F2g Raman active mode observed at 454 cm−1 belongs to CeO2. Fourier transform infra-red (FTIR) measurements showed stretching vibrations of Cu–O. The CeO2/CuO samples exhibited enhanced temperature-controlled Dc conductivity with the 4% Ce sample showing the lowest activation energy, lowest Tmax (peak value of (dσ/dT)) and consequently the maximum conductivity peaking at a temperature of 503 K. The nature of conductivity was elucidated on the basis of the carrier hopping model.

Metavalent bonding induced abnormal phonon transport in diamondlike structures: Beyond conventional theory

A phenomenon appears in a few examples of the chalcopyrites (space group $I$-42 $d$) where heavier atoms do not necessarily lead to lower lattice thermal conductivity, in contradiction with Keyes expression that formulates an inverse relation of thermal conductivity with mean atomic mass. Herewith, the thermal conductivity of $\mathrm{CuIn}{\mathrm{Se}}_{2}, \mathrm{CuIn}{\mathrm{Te}}_{2}, \mathrm{AgIn}{\mathrm{Se}}_{2}$, and $\mathrm{AgIn}{\mathrm{Te}}_{2}$ was calculated and compared at room temperature from the linearized Boltzmann transport equation using ab initio density functional theory. $\mathrm{CuIn}{\mathrm{Se}}_{2}$ and $\mathrm{AgIn}{\mathrm{Se}}_{2}$ solids exhibit lower lattice thermal conductivity than that of $\mathrm{CuIn}{\mathrm{Te}}_{2}$ and $\mathrm{AgIn}{\mathrm{Te}}_{2}$, respectively, despite the fact that Te atoms are significantly heavier than Se. A comparison between dispersion relation, the Gr\"uneisen parameter, and projected density of states leads to the conclusion that anharmonic transverse acoustic modes in the form of anomalous vibrations of Cu and Ag cause the lower values of the thermal conductivity. By analyzing the electronic structure, the compounds under study fit perfectly into a recently defined region of the metavalent bonding well known for its pronounced anharmonicity. The insight gained from the current results deepens our understanding of the unusual heat transfer phenomenon related to the metavalent bonding and sheds light on design and discovery of thermally functional materials that break the prediction by the conventional theory.

Cu0&Cu2O nanoparticles functionalized diamagnetic glasses: linear/nonlinear optical, magnetic and Faraday rotation

This paper reports Cu0&Cu2O nanoparticles synthesis and functionalized optical linear/nonlinear, magnetic and Faraday rotation properties of diamagnetic glasses. 40nm pure cubic Cu2O nanoparticles presented fingerprint Fourier transform infrared vibration at 632 cm−1 and characteristic Raman vibration of Cu(I)-O at 219 cm−1. Transparent glasses were obtained for Cu2O doping amount < 0.5 mol% under reducing environment. Cu2O modified glass structure and changed coordination of BiO3 and BO3. Cu0 and Cu+ ions co-existed, Bi4f and O1s changed with Cu2O amount. Cutoff wavelength red-shifted and a Surface Plasmon Resonance peak of Cu nanoparticles appeared at 680 nm whose intensity increased with doping amount. Under 320 nm excitation, glass showed broad and strong luminescence at 560 nm due to 3d94s1→3d10 transitions of Cu+ and Cu0. The synergetic effect of Surface Plasmon Resonance of Cu0 and electron transition of diamagnetic Cu+ greatly enhanced magnetization, nonlinearity, Verdet constant of glass (0.2097 min/G.cm) and figure of merit.

Study the influence of silver and cobalt on the photocatalytic activity of copper oxide nanoparticles for the degradation of methyl orange and real wastewater dyes

CuO (S1) Single pure component nanoparticles (SPCNPs), Ag/CuO (S2) binary component hybrid nanoparticles (BCHNPS), Co1/Ag/CuO (S3), and Co2/Ag/CuO (S4) ternary component hybrid nanoparticles (TCHNPS) were synthesized via co-precipitation method. Several spectroscopic methods investigated the characterization of the prepared catalysts. Based on Crystal properties, CuO exhibit a monoclinic phase (tenorite); the grain size of the prepared samples was 28.15 nm, 29.42 nm, 27.86 nm, and 26.67 nm for S1, S2, S3, and S4 respectively. The addition of different content from Co as a dopant to silver decorated CuO gives a clear change to a flake shape. The presence of the IR absorption peaks in the region 400–600 cm−1 matched to the distinctive stretching vibrations of Cu–O bonds in the monoclinic phase structure of CuO. Disappearance of the Raman peaks of CuO and appearing of the new characteristic peaks of cobalt oxide confirms the doping process. Using DRS analysis, arrange of the bandgap values were S1 > S2 > S3 > S4. For the synthetic methyl orange and raw industrial dye, the photodegradation parameters were measured. The results show the excellent activity of Co2/Ag/CuO NPS compared with other samples. Electrical studies of the catalysts show a higher value for the dielectric constant in the higher and lower frequency regions for the sample S4. The hopping process of the charge carrier’s improving as a result of the increase of applied field frequency which leads to an increase in the material conductivity.

Study on photocatalytic and impedance spectroscopy investigations of composite CuO/ZnO nanoparticles

This paper reports the preparation of composite CuO/ZnO nanoparticles by facile precipitation route and their photocatalytic activity against organic dyes. The red shift caused in the UV–Vis absorption spectrum suggests the enhancement of visible light photocatalytic activity of the material. The collective vibrations of Cu–O and Zn–O in FTIR spectrum clearly illustrate the formation of composite CuO/ZnO nanoparticles. Powder XRD profile suggests the formation of highly crystalline material and the chemical states of the elements is investigated by XPS analysis. A slightly agglomerated cluster-like structure of the particles is visualized by SEM analysis and EDS mapping illustrates the homogeneous distribution of the sample, which is most favorable for the photocatalysis analysis. The photocatalytic activity of material is studied against degradation of Rhodamine B and Methylene blue dyes using simulated solar light irradiation. The dielectric analysis of the composite CuO/ZnO nanoparticles demonstrates the enhanced dielectric permittivity and low loss factor in comparison with pure CuO and ZnO nanoparticles.

Copper complexation and solubility in high-temperature hydrothermal fluids: A combined study by Raman, X-ray fluorescence, and X-ray absorption spectroscopies and ab initio molecular dynamics simulations

Data for the solubility of CuS (reacting to Cu2S), Cu, and bornite + chalcopyrite + pyrite (reacting to Cu-Fe-S solid solution) in H2O + NaCl fluids were determined in situ using synchrotron-radiation X-ray fluorescence (SR-XRF) spectroscopy. The aqueous Cu concentrations ranged between 25 ppm at 500 °C, 320 MPa, 0.5 m NaCl and 760 ppm at 500 °C, 310 MPa, 4.78 m NaCl, increased with temperature along an isochore and with NaCl molality, and decreased with pressure. The X-ray absorption near edge structure (XANES) spectra of the fluid from dissolution of CuS or Cu in H2O + NaCl at 500 °C are nearly identical with published spectra of CuCl2−(aq), but differ significantly from reported spectra of Cu(I) in Cl-free hydrosulfide solutions.Raman spectra of H2O + HCl ± NaCl fluids reacted with CuS or, for comparison, metallic Cu were measured at temperatures to 600 °C and pressures to 2 GPa to test if this technique can provide additional information on the complexation of Cu(I) and on the solubility of copper in hydrothermal fluids. These spectra showed that CuCl2−(aq) was the most abundant Cu(I) species at all conditions. In addition, CuCl32−(aq) was observed at high HCl concentrations, but the Raman spectra provided no convincing evidence for Cu(I) complexation with H2S or S3− (HS−(aq) was below detection in these acidic fluids). Generally, there was an increase in the sum of the integrated intensities of the bands assigned to Cu complexes with increasing HCl concentration, and a decrease if sulfide was present. At all fluid compositions, the intensity of the Raman bands from CuCl stretching vibrations decreased with increasing pressure at constant temperature for single-phase fluids, without formation of additional bands. Based on ab initio modeling, the complexes CuCl2−(aq), Cu(HS)2−(aq), and Cu(HS)Cl−(aq) are not distinguishable by Raman spectroscopy, but the stretching vibration of Cu(I) complexes with H2S should occur at significantly lower wavenumbers.Overall, the results indicate that Cu(I) is transported predominantly as CuCl2−(aq) in reducing sulfur-free or H2S ± S3−-bearing chloridic hydrothermal fluids. The decrease in the Cu solubility in H2O + HCl ± NaCl ± H2S fluids with increasing pressure without a detectable change in speciation is caused by decrease in the formation constant of CuCl2−(aq) with pressure. Changes in the copper speciation and depressurization can be ruled out as causes for hydrothermal copper ore formation at high fluid densities above the critical density. At this condition, copper ore may precipitate by dilution, cooling in the presence of H2S, increase in pH, and/or an increase in the H2S activity.

Negative thermal expansion in 2H CuScO2 originating from the cooperation of transverse thermal vibrations of Cu and O atoms.

Negative thermal expansion (NTE) originating from the transverse thermal vibrations of metal atoms is seldom reported, which is why the transparent conducting oxide 2H CuScO2 is such a unique case. Using the density functional theory (DFT) and the quasi-harmonic approximation (QHA), the thermal properties of 2H CuScO2 were investigated. The coefficient of thermal expansion (CTE) and the Grüneisen parameters of different vibrational modes were calculated, and we found that, up to a temperature of 200 K, 2H CuScO2 displays a strong NTE behavior along the c-axis (i.e. along the O-Cu-O linkage), with an average CTE of approximately -2 × 10-6 K-1. Our calculations are consistent with the experimental values. Furthermore, we reveal that low energy modes (0-150 cm-1) originating from the cooperation of transverse vibrations of Cu and O atoms, which result in larger negative Grüneisen parameters and vibrational frequency softening phenomenon under pressure, are the main reasons for the NTE of such materials with a 2H structure. Our findings not only provide a better understanding of the NTE mechanism, but also present a report on detailed abnormal thermal properties in 2H CuScO2 that have applications in electronic, electrochemical and optoelectronic devices.

Effect of Co doped material on the structural, optical and magnetic properties of Cu2O thin films by SILAR technique

Undoped and Co doped Cu2O (Cu2−xCoxO; x = 0, 1, 2, 5 and 10) thin films were deposited onto glass substrates using successive ionic layer adsorption and reaction technique. The variation in the concentration of Co shows significant impact on the film properties, where as doped with 10 wt% of Co exhibited major property improvements when compared with other films. The prepared films were characterized for their structural, morphological, optical and magnetic properties. X-ray diffraction analysis of the films revealed the crystalline growth of Cu2−xCoxO films. The substitution of Cu2+ by Co2+ ions has led to a single phase cubic structure highly oriented along (111) plane. Optical studies (photoluminescence and UV–vis–NIR) of the films exhibit the quality of the films with the increase of dopant. The stretching vibrations of Cu–O and O–Cu–O have been confirmed by Fourier transform infrared spectroscopy. The morphological study done by a field emission scanning electron microscope has shown as increase of particle size with increase in the dopant concentration. High resolution of transition electron microscope and particle analyzer verified the nano-size and shape of the films. The presence of copper in the structure of thin film was confirmed by energy dispersive X-ray spectrometer. Magnetic measurements showed that undoped and minimum doped (1 and 2 wt%) films exhibit diamagnetic behavior and at the maximum (10 wt%) Co doping level, the films exhibit ferromagnetic properties. Current verses voltage studies showed the ohmic nature of the films.

Structural, Morphological and Ferromagnetic Properties of Pure and (Mn, Co) Codoped CuO Nanostructures

Ferromagnetic oxide semiconductor of pure and (Mn, Co) codoped CuO nanocrystals were synthesized by a chemical coprecipitation method. The phase structure, morphology and room temperature ferromagnetism were investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). Results of XRD demonstrated that both the undoped and (Mn, Co) codoped CuO samples have single phase of CuO monoclinic structure and no secondary phases were detected, suggesting the incorporation of Mn and Co dopants in CuO lattice. The FTIR spectra of all samples showed three main absorption bands attributed to stretching vibrations of Cu–O bond. The morphology of the pure CuO was found to change from nanoparticle to nanorod structure after codoping with Mn and Co ions. The diameter and length of the nanorods were nearly 28–60 and 130–550 nm, respectively. The obtained magnetic hysteresis loops at room temperature confirmed the ferromagnetic nature of all the prepared samples, which was enhanced after the incorporation of Mn and Co ions into CuO lattice. The effect of the codoped ions on the structure and ferromagnetism are discussed.

Nanostructure copper oxocobaltate fabricated by co-precipitation route using copper and cobalt nitrate as precursors: Characterization by combined diffuse reflectance and FT infrared spectra

Nanostructure copper oxocobaltate has been fabricated by a co-precipitation route using copper and cobalt nitrate as precursors. The physicochemical properties of copper cobaltate have been characterized via X-ray powder diffractometry (XRD) and field emission scanning electron microscopy (FESEM). The X-ray diffraction patterns indicates the presence of a spinel crystalline phase, (Cu0.30Co0.70)Co2O4, copper oxocobaltate with face-centered cubic lattice and Fd3m space group. FESEM images also illustrated a typical hexagonal morphology with particle size 25nm, showing a good nanoscale crystalline morphology, which corresponds well with their XRD results. The FTIR spectra confirmed the presence of hydroxyl groups bonded to the metals, stretching vibration of the cobalt–oxygen bond in an octahedral coordination and the characteristic band assigned to the vibration of Cu–O bond. UV–VIS diffuse reflectance spectrum shows a broad band over the whole visible range and broad band between 200nm and 390nm ascribed to the ligand to metal charge transfer.

High-performance thermoelectric mineral Cu12−xNixSb4S13 tetrahedrite

X-ray structural analysis and high-temperature thermoelectric properties measurements are performed on polycrystalline samples of artificial mineral Cu12−xNixSb4S13 tetrahedrite. Analysis of the atomic displacement parameter manifests low-energy vibration of Cu(2) out of CuS3 triangle plane. The vibration results in low lattice thermal conductivity of less than 0.5 W K−1 m−1. By tuning of the Ni composition x and decrease of electronic thermal conductivity, dimensionless thermoelectric figure of merit for x = 1.5 achieves 0.7 at 665 K, which is a considerably high value among p-type Pb-free sulfides. Because the tetrahedrite is an environmentally friendly material, it constitutes a good thermoelectric material for use in support of a sustainable society.

Characteristic of Raman Spectra, Crystal Structure and Superconductivity of Fe-Doped GdBa&lt;sub&gt;2&lt;/sub&gt;Cu&lt;sub&gt;3-x&lt;/sub&gt;Fe&lt;sub&gt;x&lt;/sub&gt;O&lt;sub&gt;7-δ&lt;/sub&gt; Systems

The effects of Fe doping on the structure, electronic transport properties and Raman spectra of GdBa2Cu3-xFexO7-δ (x = 0.00-0.30) systems have been investigated. The analysis of X-ray diffraction patterns shows that the compound undergoes an Orthorhombic–Tetragonal (O-T) phase transition in the doping range of x = 0.05-0.10. The superconducting transition temperature Tc decreases with the increase of Fe doping level, whereas the superconducting transition width increases abruptly with O-T transition. We have discussed the Raman shifts and intensity of the five normal phonon peaks and some other peaks which result from the vibration of Cu(1) and O(1) oxygen for the Fe doped-samples. These investigations reveal that the electronic transport properties and Raman spectra of GdBa2Cu3-xFexO7-δ composites obviously depend on O-T transition induced by the Fe doping.

Dielectric properties of CaCu3Ti4O12 prepared by sol–gel self combustion technique

The preparation of Calcium copper titanate (CCTO) nanopowder was carried out by a sol–gel self combustion method. The X-ray diffraction analysis indicated that the samples calcined at 800 °C were fully crystallized in the CCTO phase. The results of atomic force microscope showed the particles size of CCTO was in the range of 60–80 nm. The absorption bands corresponding to vibrations of Cu–O, Ti–O–Ti and νCa–O were observed at 512, 450 and 562 cm−1 using FTIR. The samples sintered at 950 °C showed the densities as high as 97% of theoretical density. The grain sizes of sintered pellets were determined by HRSEM. The dielectric properties of prepared samples were studied by LCR meter.

Weak ferromagnetic behavior, crystal structure, and electronic studies of novel [Cu(II)(Br)(PhCO 2)(Sp)] (Sp=(−)-sparteine) complex

Complex [Cu(II)(Br)(PhCO 2)(Sp)] 1 is obtained starting from copper(0), (−)-sparteine (sp) and benzoyl bromide. 1 Crystallizes in the monoclinic space group P2 1 with a=14.8857(11), b=8.9257(9), c=17.4456(14) Å, β=111.689(5)°, and Z=4. The UV–vis spectrum is characteristic of Cu(II) complexes with tetragonally distorted square pyramidal geometry. The far IR spectrum of 1 shows characteristic vibrations of Cu–Br (239 cm −1), Cu–N (437 cm −1) and Cu–O (466 cm −1) bonds. The 1H NMR broad chemical shifts of 1 integrated for a total of 31 protons and are typical of Cu(II) complexes. ESR spectra of polycrystalline 1 at 77 and 300 K show axial spectra with areas in the ratio A 77/ A 300=4.02, suggesting a very weak Cu–Cu ferromagnetic interaction. Complex 1-doped with Zn(II) gives hfs with hyperfine interaction constant value A ∥=112.45×10 −4 cm −1. The magnetization vs temperature data in the 2–299 K range, show that cupric ion pairs interact through a small antiferromagnetic Heisenberg exchange energy— J S 1· S 2 with a ground singlet state S=0, separated by J=−1.3 cm −1 from the excited triplet state S=1. The sign of the very weak interchange interaction constant, J, does not agree with the ESR spectra areas ratio of 1 at 77 and 300 K, which is a more accurate quantification of the weak ferromagnetic interaction Cu–Cu through the space.

Enhanced and correlated thermal vibrations of Cu(111) and Ni(111) surfaces

Enhanced and correlated thermal vibrations are studied for Cu(111) and Ni(111) by high-resolution medium energy ion scattering (MEIS) using the ion shadowing effect. We also perform molecular dynamics (MD) simulations based on the embedded atom method (EAM). The MEIS analysis reveals a slight contraction of $0.011\ifmmode\pm\else\textpm\fi{}0.003$ and $0.007\ifmmode\pm\else\textpm\fi{}0.003\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ for Cu(111) and Ni(111), respectively, for the first interlayer distance without any surface reconstruction. The root mean square (rms) bulk thermal vibration amplitude and thermal vibration amplitudes (TVAs) of the top-layer atoms in the surface normal and lateral directions, respectively, are determined to be $0.085\ifmmode\pm\else\textpm\fi{}0.005$, ${0.141}_{\ensuremath{-}0.005}^{+0.010}$, and ${0.094}_{\ensuremath{-}0.005}^{+0.008}\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ for Cu(111) and $0.068\ifmmode\pm\else\textpm\fi{}0.005$, ${0.098}_{\ensuremath{-}0.005}^{+0.010}$, and ${0.074}_{\ensuremath{-}0.005}^{+0.008}\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ for Ni(111). We also observe strong correlations between the nearest-neighbor atoms in the [110] string and determine the correlation coefficients to be $+0.24\ifmmode\pm\else\textpm\fi{}0.05$ and $+0.20\ifmmode\pm\else\textpm\fi{}0.05$ for Cu(111) and Ni(111), respectively, for the motion perpendicular to the [110] axis. The present MEIS result is basically in agreement with the MD simulations using the EAM potential proposed by Foiles, Baske, and Daw [Phys. Rev. B 33, 7983 (1986)] rather than that approximated by Oh and Johnson [J. Mater. Res. 3, 471 (1988)].