Preparation and capacitances of oriented attachment CuO nanosheets and the MWNT/CuO nanocomposites

CuO nanosheets formed by oriented attachment of adjacent particles and the MWNT/CuO nanocomposites have been prepared through a simple hydrothermal process. The oriented attachment of adjacent particles through [111] and [002] crystallographic planes give rise to the formation of sheetlike morphology and the related mechanisms are discussed. Some needlelike and tubelike CuO nanocrystals came into being when the nanosheets rolled up and the capacitances of as-prepared MWNT/CuO nanocomposites were measured.     

On the magnetic anisotropy of CuO

The anisotropy of the magnetic susceptibility of CuO has been measured. In both, the paramagnetic and the antiferromagnetic state the susceptibility can be described to a good approximation by

Multiferroism in the dielectric function of CuO

The multiferroic properties of bulk CuO are manifested in the dielectric function which can be triggered by an external magnetic field h and by the temperature T. Within a microscopic model and a Green's function technique we have calculated the dielectric function \varepsilon ({\bf k};T,\;h). At the magnetic phase transition temperature T_{{\rm N}2} the dielectric function offers a pronounced anomaly. This kink disappears when the magnetic field is enhanced and \varepsilon ({\bf k};T,\;h) decreases with increasing h ‐field. Both properties are indications for a strong magnetoelectric coupling in this material. The observation of multiferroism in CuO within an analytical approach is achieved by considering frustration and a linear magnetoelectric coupling. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optoelectronic characteristics of CuO nanorods

Optoelectronic characteristics of p-type CuO nanorods, synthesized by a simple hydrothermal method, were investigated at different atmospheres and oxygen pressures. The CuO nanorods have lower resistance in air than in a vacuum, unlike the n-type semiconductors. This is explained in terms of the surface accumulation conduction. Measurements at different oxygen pressures indicate that oxygen has an important effect on the optoelectronic properties of p-type nanomaterials.     

CuO/Al2O3、CuO/CeO2-Al2O3和CuO/La2O3-Al2O3催化剂中CuO物种被CO氧化的比较

用浸渍法制备了CuO/Al2O3 (Cu/Al)、CuO/CeO2- Al2O3 (Cu/CeAl)和CuO/La2O3-Al2O3(Cu/LaAl)催化剂. 通过原位XRD、Raman和H2-TPR方法， 对催化剂中的CuO物种以及CuO-Al2O3的固-固相反应进行了表征. 结果表明，对于Cu/Al催化剂，CuAl2O4存在于CuO与Al2O3层之间，CuO以高分散和晶相两种相态存在于催化剂的表层；对于Cu/CeAl催化剂，除了少量高分散和晶相的CuO存在于表层外，大部分CuO迁移到了CeO2的内层，     

Bi系高温超导体CuO2面外Cu-O键伸缩振动的理论分析

根据分子振动理论,采用简化模型分析了Ｂｉ系高温超导体ＣｕＯ２面外Ｃｕ－Ｏ键伸缩振动的振动模式,计算了振动频率,并将结果与实验分析结果进行了比较。     

Relaxation of radiation-induced defects in CuO

The relaxation of radiation-induced defects in the CuO polycrystal and nanoceramic with the particle size d = 15 nm irradiated by an electron dose of F = 5 × 10¹⁸ cm^?2 has been studied. In the irradiated samples, a strong susceptibility increase with decreasing temperature T < 150 K is observed. This increase is due to the formation of ferromagnetic polarons in the antiferromagnetic matrix near the defects. The structural symmetry distortion makes the samples unstable. The time variations of the magnetic properties in the CuO samples prepared by different methods are compared.     

Electronic structure and spectra of CuO

We report the electronic structure of monoclinic CuO as obtained from first principles calculations utilizing density functional theory plus effective Coulomb interaction (DFT + U) method. In contrast to standard DFT calculations taking into account electronic correlations in DFT + U gave antiferromagnetic insulator with energy gap and magnetic moment values in good agreement with experimental data. The electronic states around the Fermi level are formed by partially filled Cu 3d _x²?y² orbitals with significant admixture of O 2p states. Theoretical spectra are calculated using DFT + U electronic structure method and their comparison with experimental photoemission and optical spectra show very good agreement.     

Temperature-dependent magnetic anomalies of CuO nanoparticles

Copper oxide (CuO) nanoparticles with an average size of 25 nm were prepared by a sol-gel method. A detailed study was made of the magnetization of CuO nanoparticles using a maximum field of 60 kOe for temperatures between 8 and 300 K. Antiferromagnetic CuO nanoparticles exhibit anomalous magnetic properties, such as enhanced coercivity and magnetic moments. Significantly, the magnitude of the hysteresis component tends to weaken upon increase in temperature (>8 K). In addition, a hysteresis loop shift and coercivity enhancement are observed at 8 K in the field-cooled (FC, at 50 kOe) case. It is thought that the change in hysteresis behavior is due to the uncompensated surface spins of the CuO nanoparticles. The susceptibility (χ) plot showed that χ varied substantially at temperatures below 12 K, and this transition is due to the exchange interactions between the neighboring atoms at the nanoscale.     

Anomalous magnetic behavior of CuO nanoparticles

We report studies on temperature, field and time dependence of magnetization on cupric oxide nanoparticles of sizes 9 nm, 13 nm and 16 nm. The nanoparticles show unusual features in comparison to other antiferromagnetic nanoparticle systems. The field cooled (FC) and zero field cooled (ZFC) magnetization curves bifurcate well above the Néel temperature and the usual peak in the ZFC magnetization curve is absent. The system does not show any memory effects which is in sharp contrast to the usual behavior shown by other antiferromagnetic nanoparticles. It turns out that the non-equilibrium behavior of CuO nanoparticles is very strange and is neither superparamagnetic nor spin glass like.     

High energy spin dynamics of La2CuO4 and La1.9Sr0.1CuO4

The magnetic excitations in La₂CuO₄ and La_1.9Sr_0.1CuO₄ were studied by inelastic neutron scattering up to energies of 76 meV. For the pure sample, the results forE15 meV can be well described by conventional spin wave theory with a spin wave velocity c=0.89±0.07 eVÅ. For lower energies, the observed intensities were somewhat higher than expected from spin wave theory and did not follow the Bose-Einstein factor. For the doped sample, the linewidth in constant-E scans at smallE shows a very short correlation length of =7.5 Å only, which is considerably below the value expected from the concentration dependence reported by other authors. An increase of the linewidth for largeE indicates a reduced spin-wave stiffness when compared to the undoped material. However, the use of a spin-wave picture may not be appropriate as the standard expression for damped spin waves in a paramagnetic material is in serious conflict with experiment.     

Electronic structure of (LaSr)2CuO4 and (NdCe)2CuO4

The electronic structure of (LaSr)₂CuO₄ and (NdCe)₂CuO₄ are compared. It is concluded that in both materials after doping by holes and electrons respectively the Fermi energy is at the top of the valence band. This explains many symmetrical properties and in particular the photoemission experiments.Dedicated to Prof. P. Kienle on the occasion of his 60th birthday     

Dual character of the electronic structure of YBa2Cu4O8: the conduction bands of CuO2 planes and CuO chains

We use microprobe angle-resolved photoemission spectroscopy (microARPES) to separately investigate the electronic properties of CuO2 planes and CuO chains in the high temperature superconductor, YBa2Cu4O8. For the CuO2 planes, a two-dimensional (2D) electronic structure is observed and, in contrast to Bi2Sr2CaCu2O8+delta, the bilayer splitting is almost isotropic and 50% larger, which strongly suggests that bilayer splitting has no direct effect on the superconducting properties. In addition, the scattering rate for the bonding band is about 1.5 times stronger than the antibonding band and is independent of momentum. For the CuO chains, the electronic structure is quasi-one-dimensional and consists of a conduction and insulating band. Finally, we find that the conduction electrons are well confined within the planes and chains with a nontrivial hybridization.     

Resonance Raman spectra of the Ca2CuO3 cuprate

Ceramics of the Ca₂CuO₃ cuprate with a purely chain copper-oxygen structure is synthesized. The Raman spectra of ceramic samples are recorded upon excitation in a broad spectral range from the blue-green to near-IR region. The intensities of a number of lines and bands of different scattering orders are estimated using the internal reference method. The results are compared with physical and chemical models of the process.