CuO4 Single Crystal Research Articles

Crystal growth of KCl:CuO single crystal starting from inhomogeneous solid-melt phase using the Czochralski method

In this work the Czochralski technique was employed to grow a pure KCl and KCl:CuO single crystals, these crystals were grown starting from homogeneous and heterogeneous phases, respectively. The heterogeneous phase consists two different phases which are KCl as melting phase and CuO nano-crystals (NCs) as a solid state phase. Due to the high temperature of the crystal growth environment this approach has a big challenge to keep NCs in the solid state phase during the crystal growth process. To control and analyze the obtained crystals, several techniques of characterization were used to investigate the structural and optical properties of CuO NCs dispersed in a crystalline medium (KCl). The main structural results of X ray diffraction (XRD), Raman, and IR spectroscopy prove the presence of nanocrystallites with monoclinic phase of CuO, where the estimated average size is aproxmetly 30 nm. Quantitative analyzes of elements using the energy-dispersive X-ray spectroscopy (EDX) demonstrates the high purity of samples. Moreover, the optical properties were investigated using UV–Vis spectroscopy and photoluminescence (PL), where CuO crystallites exhibit three bands located at 450 nm, 557 nm, and 594 nm with blue shift as a comparison of bulk CuO, this blue shift is a result of nanoscale of CuO. The presence of CuO NCs in the crystalline medium (KCl) enhances the PL properties; this feature makes the obtained crystal an excellent candidate for integration into optical devices that operate within the visible range, particularly between 450 and 600 nm.

Impact of rGO Concentration on the Physical Characteristics of CuO/rGO Nanocomposite for Sensing and Optoelectronic Applications

Facile synthesis demonstrated formation of CuO/rGO composite for enhanced optical and electrical characteristics for sensing and photonic devices. CuO nanoparticles synthesized using sol-gel method and various rGO percentages (10%–30%) were loaded to form composite via ultra-sonic assisted technique. Structural study using XRD and TEM confirms the formation of CuO polyhedral nanoparticles with monoclinic structure showing deviations in the unit cell parameters, crystallite size, axis strain. These deviations cause transformation of polyhedral particles into rod shaped nanocomposites with embedded CuO single crystals with changed rGO. X-ray photoelectron spectroscopy showed varied elemental composition of CuO/rGO nanocomposites having Cu2+ chemical state. Optical measurements exhibit modified direct (1.54 eV–1.51 eV) and indirect bandgap (1.38 eV–1.31 eV) having higher absorption in Visible to NIR region for photovoltaic applications. Raman spectroscopy and FTIR confirms the presence of Raman active bands and functional groups corresponding to Cu-O. Electrical measurements shows decreased resistance with increased incorporation of rGO. The higher presence of oxygen sites and low resistance facilitate easy electron transport alongwith an optimum bandgap (1.51 eV) and higher absorption in Visible to NIR region showed possible utility of the grown nanoparticles and composites in gas/photo sensing and optoelectronic applications.

Nanoporous CuO mesocrystals: Low-temperature synthesis and improved structure-performance relationship for energy storage system

Uniform nanoporous CuO mesocrystals are synthesized through a low-temperature hydrothermal strategy. The ordered CuO mesocrystal superstructures are assembled by the adsorption of small n-butylamine molecules, which can be easily removed during the subsequent washing process. The CuO mesocrystals demonstrate excellent electrochemical performance for both lithium storage and supercapacitors as compared with CuO single crystals and polycrystals. Our study reveals the structure-performance relationship among the electrochemical performance, morphology, and crystallography construction, which can guide us to optimize the structure of electrode materials for energy storage system.

CuO nanocrystals embedded in KBr single crystal: Elaboration and characterization

More recently, there are important number of papers which have been stimulated by the optical characteristics of crystalline matrixes doped with quantum dots (QDs), nanoparticles (NPs) or nanocrystals (NCs) of semiconductors. In this context, we suggest this investigation, which highlights the doping effects of CuO (NCs) on structural and optical properties of KBr single crystal. In this approach, we expose a simple and realizable technique for embedding CuO NCs as three dimensions (3D) defects in a KBr crystalline matrix. The Czochralski method was used to obtain a KBr:CuO single crystal starting from inhomogeneous phase melt-NCs in the crystallization melting-pot. However, the nano-regime of guest material creates a difficult challenge, because there is a possibility of fusing of the CuO NCs during the crystal growth process. Nevertheless, the whole structural results prove that the NCs inside KBr:CuO single crystal have monoclinic phase with nano-regime size. In addition, these results appear that the CuO NCs have two orientations preferred inside KBr host and demonstrate that the chemical bond CuO of CuO monoclinic phase steel exists. Relative to the optical properties, the UV–visible absorption spectroscopy exhibits that the NCs inside KBr:CuO sample have a nano-regime size, where the band gap shifts toward the higher energies. Furthermore, photoluminescence (PL) of KBr:CuO single crystal appears an important intensity in the visible range, this property makes this sample as a good candidate to integrate them in the optical devices which are working in the visible range.

Magnetotransport at the LTO-LTT Structural Transition in La1.48Nd0.4Sr0.12CuO4

Magnetoresistance (MR) was measured in a La1.48Nd0.4Sr0.12CuO4 single crystal in perpendicular magnetic fields H up to 9 T in the region of the structural transition from the low-temperature orthorhombic (LTO) to low-temperature tetragonal (LTT) phase. The hysteretic MR exhibits discrete jumps or avalanches only when the transition is approached from the LTT phase, and only during the first field sweep. The properties of the hysteresis are found to be independent of the field driving rate. The results are consistent with the presence of magnetostructural domains coupled with the charge degrees of freedom.

Extended Drude model analysis of n-doped cuprate, Pr0.85LaCe0.15CuO4

We investigated optical properties of an electron-doped copper oxide high temperature superconductor, Pr0.85LaCe0.15CuO4 (PLCCO) single crystal. We obtained the optical conductivity from measured reflectance at various temperatures. We found our data contained c-axis longitudinal optical (LO) phonon modes due to miscut and intrinsic lattice distortion. We applied an extended Drude model to study the correlations between charge carriers in the system. The LO phonons appear as strong sharp peaks in the optical scattering rate. We tried to remove the LO phonon modes by using the energy loss function, which also shows the LO phonons as peaks, and could not remove them completely. We extracted the electron-boson spectral density function using a generalized Allen's formula. We observed that the resulting electron-boson density show similar temperature dependence as hole-doped cuprates.

Laser induced modification of the properties of CuO single crystals coated by metal film

The properties of copper oxide CuO single crystals coated by Cu or Ag films before and after the surface treatment by YAG:Nd3+ laser radiation were studied. With an increase of energy density of laser radiation the drastic changes in the surface microstructure, elemental composition and electrical properties of the crystals under investigation were observed. The peculiarities inherent to the granular samples have not been revealed on the temperature dependence of the resistance. The modification of copper oxides properties by the influence of laser irradiation may be used to improve the characteristics of various devices based on them.

Behaviour of the second magnetization peak in La2−Sr CuO4 single crystals upon entering the doping domain of static stripe order

Abstract The occurrence of a second magnetization peak (SMP) on the dc magnetization curves of superconducting single crystals with random quenched disorder in increasing external magnetic field H is quite common. Many models for this intriguing phenomenon have been proposed so far, but its origin is still under strong debate. Optimally doped and overdoped La2−xSrxCuO4 single crystals (x ≥ 0.15) exhibit an SMP over a large temperature interval, up to very close to the critical temperature. By decreasing doping, it was found that with H oriented along the c axis the SMP completely disappears in the doping domain of well developed static charge and spin stripes (x ∼ 1/8), reappearing for x ≤ 0.10. This behaviour follows the instability of the Bragg vortex glass generated by the static stripe order (as revealed by small-angle neutron scattering experiments), which is confirmed by our magnetization relaxation measurements. If H is along the (a, b) planes, the SMP is observed for all investigated specimens. The presented analysis supports the scenario in which the SMP is generated by the pinning-induced disordering of the low-field Bragg vortex glass in the dynamic conditions of dc magnetic measurements.

CuO single crystal with exposed {001} facets--a highly efficient material for gas sensing and Li-ion battery applications.

Single crystal copper oxide nanoplatelets with a high percentage of {001} facets were synthesized by a facile hydrothermal approach. The as-prepared materials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and high resolution transmission microscopy. Via density functional theory calculations, it was found that the {001} facets are active crystal planes. When the single crystal CuO nanoplatelets were applied as an anode material in Li-ion batteries, they demonstrated outstanding electrochemical performance with high lithium storage capacity, satisfactory cyclability, and excellent high rate capacity. When used as a sensing material in gas sensors, they exhibited a superior sensitivity towards toxic and flammable gases.

Stripe order related in-plane fourfold symmetric superconductivity in La1.45Nd0.4Sr0.15CuO4 single crystal

The in-plane fourfold symmetry of the upper critical field Hc2 in a stripe-ordered La1.45Nd0.4Sr0.15CuO4 single crystal has been observed through measuring the out-of-plane resistivity ρc by rotating the crystal around its c-axis in magnetic fields parallel to the ab-plane of the crystal. It was found that the upper critical field Hc2 takes maxima (minima) for magnetic fields along Cu-O-Cu (Cu-Cu) direction, suggesting an intrinsic fourfold superconductivity. The results should be closely related to the special structure of the charge stripes which are along Cu-O-Cu direction and rotated 90° in adjacent CuO2 planes, and the fourfold symmetry behaviors in Hc2 and ρc can be well described by a scaling method. The stripe phase can also lead to a fourfold vortex pinning effect which is confirmed by the angular dependence of the irreversibility field Hirr and the activation energy U for flux motion.

Second-order Raman scattering in CuO

Polarized second-order Raman scattering spectra of CuO single crystals are reported. It is shown that for some scattering geometries the second-order processes dominate the inelastic light scattering spectra. Group-theoretical symmetry analysis of the selection rules for the first- and second-order scattering processes is performed and phonon dispersion relations are calculated within density functional theory. The main spectral features of the two-phonon spectra are assigned to overtones of the vibrational branches at various special points across the Brillouin zone.

Anisotropy of the upper critical fields and the paramagnetic Meissner effect in La1.85Sr0.15CuO4 single crystals

Optimally doped La1.85Sr0.15CuO4 single crystals have been investigated by dc and ac magnetic measurements. These crystals have rectangular needle-like shapes with the long needle axis parallel to the crystallographic c axis (c-crystal) or parallel to the basal planes (a-crystal). In both crystals, the temperature dependence of the upper critical fields (HC2) and the surface critical field (HC3) were measured. The H–T phase diagram is presented. Close to TC = 35 K, for the c-crystal, , whereas for the a-crystal the obtained is much higher than 1.69, predicted by the ideal mathematical model. At low applied dc fields, positive field-cooled branches known as the ‘paramagnetic Meissner effect’ (PME) are observed; their magnitude is inversely proportional to H. The anisotropic PME is observed in both a- and c-crystals, only when the applied field is along the basal planes. It is speculated that the high γa and the PME are connected to each other.

Rapid synthesis of CuO nanoribbons and nanoflowers from the same reaction system, and a comparison of their supercapacitor performance

One-dimensional CuO nanoribbons and three-dimensional CuO nanoflowers were synthesized via a facile, rapid, low-temperature, one-pot water bath method, in which the synthesis was performed in Cu(CH3COO)2/NaOH and aqueous/ethanol systems at 70 °C for 15 min. Control over the shape and dimensionality of the well-defined CuO single crystals was achieved simply by varying the order of addition of the reactive materials. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction were used to characterize the products. The formation mechanism in the in situ, rapid reaction was investigated. In Brunauer-Emmett-Teller and thermogravimetry measurements, the nanoribbons exhibited a higher specific surface area and higher adsorption capabilities than the nanoflowers. Using cyclic voltammetry, chronopotentiometry and EIS measurement for supercapacitance, it was shown that the nanoflower electrodes had better performance than the nanoribbon electrodes, however, the nanoribbon/C electrodes had better performance than the nanoflower/C electrodes at lower current density, but were worse at higher current density.

Stripe order in superconducting La2−xBaxCuO4(0.095⩽x⩽0.155)

The correlations between stripe order, superconductivity, and crystal structure in La(2-x)Ba(x)CuO(4) single crystals have been studied by means of x-ray and neutron diffraction as well as static magnetization measurements. The derived phase diagram shows that charge stripe order (CO) coexists with bulk superconductivity in a broad range of doping around x=1/8, although the CO order parameter falls off quickly for x<>1/8. Except for x=0.155, the onset of CO always coincides with the transition between the orthorhombic and the tetragonal low temperature structures. The CO transition evolves from a sharp drop at low x to a more gradual transition at higher x, eventually falling below the structural phase boundary for optimum doping. With respect to the interlayer CO correlations, we find no qualitative change of the stripe stacking order as a function of doping, and in-plane and out-of-plane correlations disappear simultaneously at the transition. Similarly to the CO, the spin stripe order (SO) is also most pronounced at x=1/8. Truly static SO sets in below the CO and coincides with the first appearance of in-plane superconducting correlations at temperatures significantly above the bulk transition to superconductivity (SC). Indications that bulk SC causes a reduction of the spin or charge stripe order could not be identified. We argue that CO is the dominant order that is compatible with SC pairing but competes with SC phase coherence. Comparing our results with data from the literature, we find good agreement if all results are plotted as a function of x' instead of the nominal x, where x' represents an estimate of the actual Ba content, extracted from the doping dependence of the structural transition between the orthorhombic phase and the tetragonal high-temperature phase.

Two-component dynamic responses of vortex matter near the vortex melting line in superconductingLa1.86Sr0.14CuO4 single crystals

We report the dynamics of moving vortices inLa1.86Sr0.14CuO4 single crystals studied via a transient voltage response (TVR) near the vortex meltingtransition. In the TVR signal, we could identify two types of relaxation caused byrearrangement of the vortex configuration. Based on careful temperature- andfield-dependent measurements of these two components, we suggest that the fastcomponent results from moving of the stable ordered vortex phase, while the slow one isgenerated during the annealing process of the metastable disordered vortex phase, which isinjected through the surface. As the temperature is lowered across the melting line, themetastable disordered phase in the heterogeneous mixture gets a longer life time dueto the reduced thermal fluctuations, occupying a larger portion of the sample.Consistent with this picture, the boundary of the slow relaxation is coincident withthe irreversibility line, which is known to be a property of the surface barriers.

Effect of Redistribution of the Optical Spectral Weight in CuO Nanostructured Ceramics

Features of the optical properties of nanostructured samples of cupric oxide CuO prepared by shock wave loading (SWL) and by high pressure torsion (HPT) methods have been investigated by means of spectroscopic ellipsometry in the range of 0.5-5.0 eV. The results for nanostructured samples are discussed in comparison with the measurement data of the CuO single crystal. Dispersion of the components of the complex permittivity in nanostructured CuO samples is significantly different from that for the single crystal. The optical spectral density of the nanostructured CuO is redistributed from the energy region above the fundamental absorption edge to the region below the edge. The shift is unexpected strong for samples prepared by the HPT method. The intensity of the optical spectra is suppressed in the range above the fundamental absorption edge and increases in low-energy one. It has been shown that the energy positions of the main electronic transitions in nanostructured samples on the whole are the same as in the single crystal; at the same time, intensity of the low-energy transitions increases. The possible causes of this increase and resolution of the fine absorption structure of the nanostructured CuO are discussed.

Charge order and low frequency spin dynamics in lanthanum cuprates revealed by Nuclear Magnetic Resonance

We report detailed 17O, 139La, and 63Cu Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) measurements in a stripe ordered La1.875Ba0.125CuO4 single crystal and in oriented powder samples of La1.8-xEu0.2SrxCuO4. We observe a partial wipeout of the 17O NMR intensity and a simultaneous drop of the 17O electric field gradient (EFG) at low temperatures where the spin stripe order sets in. In contrast, the 63Cu intensity is completely wiped out at the same temperature. The drop of the 17O quadrupole frequency is compatible with a charge stripe order. The 17O spin lattice relaxation rate shows a peak similar to that of the 139La, which is of magnetic origin. This peak is doping dependent and is maximal at x ~ 1/8.

The anomalous anisotropy in the ac susceptibility of La1.45Nd0.4Sr0.15CuO4 single crystal

The dependencies of ac susceptibility on the superimposed dc magnetic fields for the stripe-ordered La1.45Nd0.4Sr0.15CuO4 single crystal with two superconducting transitions have been studied in the 3D and 2D superconducting ranges for the fields along different orientations of the crystal. The results show that with increasing fields the interlayer Josephson coupling and the in-plane superconductivity are suppressed orderly for the fields perpendicular to CuO2 planes. The influences of the field parallel to CuO2 planes on the 3D and 2D superconductivity are much weaker than those of the field parallel to the c-axis. The irreversibility lines for the 3D and 2D superconducting states are also studied.

Temperature dependence of tunneling conductance on an overdoped Pr0.82LaCe0.18CuO4 with [formula omitted

We present tunneling conductances on electron-doped Pr0.82LaCe0.18CuO4 (PLCCO) single crystals with Tc∼16K that are in overdoped regime. Our data exhibit reproducible superconducting-gap peaks at 4.44±0.71mV and the subgap-shape is cusplike which can be fitted well by using d-wave or nonmonotonic d-wave symmetry, showing that PLCCO is a superconductor with nodal gap. Furthermore, we found that the temperature dependence of the gap magnitude is BCS like and it disappeared at Tc. We conclude that these characteristic features (such as d-wave order parameter and no pseudogap above Tc) of electron-doped cuprates in the overdoped regime are fundamentally similar to those of hole-doped cuprates in the overdoped regime.

Phonon softening in [formula omitted] studied by inelastic X-ray scattering

The phonon dispersions in the CuO2 planes are measured in La1.74Eu0.1Sr0.16CuO4 single crystals using high-resolution inelastic X-ray scattering at BL35XU of SPring-8. The oxygen bond-stretching mode shows anomalous phonon softening (a dip in the dispersion with phonon peak broadening) at Q∼1/3, which coincides with the wave vector of stripe charge modulation. The result indicates that strong electron–electron correlations, in the form of charge-ordering, create a strong electron–phonon coupling in high-temperature superconductors.