Copper Oxide Structures Research Articles

Application of Multivariate Data Analysis Techniques in Modeling Structure–Property Relationships of Some Superconductive Cuprates

Multivariate analysis methods are used for the examination of the fine structure and superconductivity properties of the 1212-type superconductive copper oxides with the stoichiometry of MA2QCu2O6+z (M=Cu, Hg, Tl/Pb; A=Ba, Sr; Q=rare-earth element, Ca; z=0–1). PCA (principal component analysis) is used for the qualitative evaluation of relations between structural variables such as the cation–oxygen bond lengths, bond angles, and oxygen content z, and the superconductivity transition temperature TC, adopted from a number of neutron diffraction studies published for MA2QCu2O6+z samples with various compositions. The different ways of doping positive holes in the superconductive CuO2 plane are discussed on the basis of the PCA results. Quantitative modeling of the value of TC in the CuA2QCu2O6+z system is successfully performed by PLS (projections to latent structures by means of partial least squares), resulting in a model with predictive power of ∼93%. The present study demonstrates the potential of multivariate analysis methods in studying structure–property relations of inorganic materials with ionic structure.

X-ray photoelectron spectroscopy and Auger electron spectroscopy investigation on the oxidation resistance of plasma-treated copper leadframes

X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) have been employed in the investigation of the surface chemistry and oxidation-resistant property of the C-, N-, and Cu-containing films, formed by the plasma treatment of pristine copper. The copper oxidation process has been elucidated using realistic microelectronic packaging-assembly conditions, results of which are in agreement with established models. From the chemical shift in binding energy and change in full-width-half-maxima of the XPS core-level peaks, the heated copper has been observed to first form the monovalent cuprous oxide (Cu2O) followed by nucleation and growth of the divalent cupric oxide (CuO) above the Cu2O. The copper hydroxide [Cu(OH)2] has been observed to form on the Cu2O, CuO, and copper metal surfaces. This knowledge of copper oxidation has been used as a yardstick for the study of film decomposition and subsequent oxidation of exposed copper. Variation of the plasma treatment time produced two films of varied thickness [CuCxNy(A):15 nm and CuCxNy(B):75 nm], with the longer time producing the thicker films. AES results also suggest that the two films have the analogous film stoichiometry of 1:1:0.16 (Cu:C:N). Further XPS and AES analyses reveal the thickness dependence of the oxidation-resistant property, with the thicker film having the better oxidation resistance. A difference in film thickness of ∼5 times delayed the film decomposition temperature by 50 °C. AES depth profiles on the heated (250, 300, and 350 °C) films show the gradual decay of the film thickness with heating temperatures. Oxide growth predominates with the complete decomposition of the films. Present results suggest neither the presence of entrapped N2 gas in the copper oxide structure nor an oxide structure with the C and N decorations at the copper oxide grain boundaries. One possible film decomposition mechanism may be through the breaking of the Cu–N bonds under suitable heating conditions, thereby allowing the formation of the Cu–O bonds as the oxidation proceeds.

Control of the charge inhomogeneity and high-Tc superconducting properties in homologous series of multi-layered copper oxides

A systematic view stemmed for the most important parts from the authors’ own research results is presented for tailoring high-Tc superconductive copper oxides from the standpoint of materials chemistry. The present article first elucidates that, in the multi-layered superconductive copper-oxide structures presently known to exist, the distribution of charge/charge carriers is inhomogeneous over several different spatial dimensions throughout the crystal. At the same time useful guiding rules are derived based on the concepts of tolerance parameter and bond-valence for controlling the charge distribution. Then experimental and semi-experimental evidences are presented to establish the relationships between the inhomogeneous distribution of holes and superconducting properties. To reach this goal, phenomenological aspects of the high-Tc superconductive copper oxides are described systematically, and selected important techniques for estimating the local carrier concentration and distribution are discussed. That is, the following points are included in the present article: (i) general crystallographic categorization and naming scheme of multi-layered copper oxides based on the concept of homologous series, (ii) crystallographic and chemical factors to control the oxygen non-stoichiometry and charge distribution, (iii) techniques for probing the charge/carrier distribution in the layered copper-oxide crystal, and (iv) empirical relationships between the carrier distribution and superconducting properties including the superconductivity transition temperature, Tc, the magnetic irreversibility field, Hirr, and the so-called peak effect/fishtail phenomenon. Finally, the unified view is summarized and some indespensable questions to be still answered in future work are mentioned.

Re-examination of the non-stoichiometry and defect structure of copper(II) oxide or tenorite, Cu 1± zO or CuO 1± ϵ: A short review

Four sets of compositional data with a departure z or ϵ from the stoichiometry of tenorite Cu 1± z O or CuO 1± ϵ are re-examined for possible point defects. Correlations z( p O2) at equilibrium solid⇔pure di-oxygen – when they can be computed – indicate the presence of either oxygen vacancies or copper interstitials or clusters of them. Some recent data after quenching are in favor of copper interstitials. Few data concerning tenorite prepared by decomposition of a salt, by oxidation of copper and by CVT in sealed tubes have generally been interpreted in the literature as indicating copper deficiency. In those oxides a large departure from the stoichiometry indicates a complex behavior likely due to several point defects possibly ordering at short and/or long range, and including chemical impurities in the case of sealed tube preparation. It is, however, in fact likely that the defect structure of such samples involves the two sub-lattices. Cu 3O 2- or Cu 4O 3-like clusters can even be envisaged.

The Electronic Structure and Bonding of Copper Oxides by CBED and EELS

Abstract Cu2O and CuO are of great interest after the discovery of the high Tc superconductors. The superconductivity is believed to be dependent on charge states in CuO2 layers whose structure is similar to that of CuO. These transition-metal compounds are also important because of the different copper coordination numbers and different copper-oxygen distances, therefore these reflect different electron density distributions and bonding mechanisms. The electronic structure of cuprite has been studied extensively both theoretically and experimentally because of its symmetrical crystallographic structure (space group ) while that of CuO (space group C2/c) which has a monoclinic structure has been studied only recently. Previous experimental and theoretical results show that the valence electrons of copper in cuprite form hybrid states which is proposed by Orgel instead of spherical d10 state as in ionic copper.

Superconductivity at 25.5 K in electron-doped layered hafnium nitride

The electronic properties of crystals with a layered structure can be radically altered by the intercalation, between the layers, of guest species that act as electron donors or acceptors. Such studies have been performed extensively on graphite, transition-metal dichalcogenides and oxide bronzes1. Interest in redox intercalation reactions2 has increased recently because the high-transition-temperature (high-Tc) superconductors based on copper oxide also have layered structures, the superconductivity occurring within two-dimensional CuO2 planes separated by charge-reservoir oxide layers3. Similarly, in metal-doped fullerenes, which show relatively high transition temperatures, the electron donor atoms sit in the interstitial sites between adjacent fullerene balls4. In a previous study5, we described a layered nitride, β-ZrNCl, consisting of Zr–N double layers sandwiched between two close-packed chlorine layers. On lithium intercalation, the crystal changed from a semiconductor to a metal, and became a superconductor at 13 K. Here we report the properties of the isostructural compound β-HfNCl. After electron-doping the crystal by lithium intercalation, we observe superconductivity with a Tc of up to 25.5 K. This transition temperature is higher than that observed in any intermetallic compound, and suggests that layered nitride structures may offer transition temperatures comparable to those observed in layered copper oxide structures.

Effect of electron bombardment on a phase-inhomogeneous nanoscopic structure and the fundamental absorption spectrum of single-crystal CuO

The optical absorption spectra of single-crystal CuO bombarded with 5-MeV electrons exhibit reduced absorption in the region of the fundamental absorption edge at 17 eV, which corresponds to the b1g→eu transition with charge transfer in CuO 4 6− . A simultaneous increase in absorption is observed in the middle infrared and in the region of high energies centered on 2.9 eV. The experimental results obtained are interpreted in terms of ideas on the phase-inhomogeneous nano-agglomorated structure in copper oxides that occurs as a result of the nucleation of polar centers (CuO 4 5− , CuO 4 7− ) under electron bombardment.

C Axis Superfluid Response of Copper Oxide Superconductors.

A novel interplay between d-wave superconducting order parameter symmetry and the underlying Cu 3d orbital based electronic structure of Copper-Oxides leads to a striking anisotropy in the superfluid response of these systems. In clean tetragonal materials the c-axis penetration depth increases as T^5 at low temperature T, in contrast to linear T behavior in the ab-plane. Disorder is a relevant perturbation which causes all components of the superfluid response to depend quadratically on temperature at low temperature. However, the cross-over temperature scale from the intrinsic d-wave behavior to the disorder dominated behavior for the in-plane response may be different from that for the out-plane response.

Die Molekül- und Kristallstruktur der Kupfer-, Aluminium-und Kaliumkomplexe des Cyclohexyl-hydroxy-diazeniumoxids1

Abstract The crystal structures of copper, aluminium and potassium cyclohexyl(hydroxy)diazenium oxide (2) have been determined at 203 K. Yellow crystals of C18H33AlN6O6 are triclinic, space group P[unk] a = 9.459(1) Å, b = 11.986(1) Å, c = 20.599(2) Å, α = 92.36(1)°, β = 91.65(1)°, γ = 92.69(1)°, Z = 4 and Dx = 1.311 Mg m−3. Light blue crystals of C12H22CuN4O4 are monoclinic, space group P21/c, a = 12.944(3) Å, b = 5.001(1) Å, c = 11.716(2) Å, β = 97.90(1)°, Z = 2 and Dx = 1.547 Mg m−3. Colorless crystals of C6H11KN2O · H2O are monoclinic, space group P21/c, a = 5.507(1) Å, b = 32.208(4) Å, c = 10.289(1) Å, β = 90.01(1)°, Z = 8 and Dx = 1.458Mg m−3. The structures have been solved by direct methods and refined with a full-matrix leastsquares procedure; C18H33AlN6O6: R(F) = 0.056, 5972 independent reflections; C12H22CuN4O4: R(F) = 0.045, 974 independent reflections; C6H11KN2O2 · H2O: R(F) = 0.099, 2374 independent reflections. In all three complexes the bidentate hydroxy-diazeniumoxide ligand coordinates the metal ion through its oxygen atoms. In the copper complex the metal is rectangular planar coordinated. The Al complex shows the central ion in octahedral environment. In both cases, discret molecular entities are observed that are connected in the crystal through van der Waals contacts. The potassium ion is surrounded by seven oxygen atoms of which four are part of two bidentate ligands coordinating the ion in a chelate-type fashion. Two remaining ones belong to ligands bridging between neighboring potassium ions. The seventh coordination site is occupied by a water molecule.

Combustion of CO and Toluene; Characterisation of Copper Oxide Supported on Titania and Activity Comparisons with Supported Cobalt, Iron, and Manganese Oxide

Titania-supported copper oxide catalysts have been prepared with loadings in the range from 13 to 5 theoretical layers and have been tested for the combustion of CO and toluene. Characterisation with XRD, electron microscopy, EDX, TPR, Raman, and XPS gives details about the structure of copper oxide on titania. The results show that dispersed CuOxis formed up to a loading of about one theoretical layer. TPR indicates the formation of two types of dispersed species, which possibly are isolated and polymeric, respectively. XPS data show that the dispersed copper is Cu2+. The dispersed species have high catalytic activity for combustion. At higher copper oxide loading, bulk CuO is formed, contributing little to the activity. Comparison of three titania supports with differing surface area and pore size distribution shows that the most favorable is a support with a surface area of about 38 m2/g and mesopores in the range 100–800 Å. The longevity of the catalysts was tested in the waste gas from a formaldehyde plant. Deactivation was observed after being on stream for 57 days, and the deactivation is due to sintering of both the support and the copper oxide. Copper oxide on titania is shown to be more active than cobalt, manganese, and iron oxide on the same support.

Synthesis and Crystal Structure of New Pb-Based Copper Oxides (Pb0.5M0.5)(Sr0.9Ho0.1)2(Ho0.7Ce0.3)2Cu2Oy(M= Pb and Cd)

New Pb-based copper oxides (Pb0.5M0.5)(Sr0.9Ho0.1)2(Ho0.7Ce0.3)2Cu2Oy(M= Pb and Cd) have been synthesized successfully. The structure of the compounds has been determined using the powder X?ray diffraction data. It is found that the lattice parameters area= 3.8368 Å andc= 29.1894 Å for the compound withM= Pb anda= 3.8168 Å andc= 29.3372 Å forM= Cd. XRD results show that the structure is isostructural with (Pb, Cu) (Sr,R)2(R′, Ce)2Cu2Oz(R,R′ = rare earth elements).

Size-induced structural transitions in the Cu-O and Ce-O systems.

We have studied the effect of reducing the particle size on the crystal structures of copper oxide and cerium oxide. Below 25 nm, the cubic ${\mathrm{Cu}}_{2}$O is found to be more stable than the monoclinic CuO. This confirms an earlier conjecture that the ionic character of a solid tends to increase with a reduction in the particle size. As a result, high-symmetry crystal structures are more likely to be stable at smaller sizes. For cerium oxide, the bulk (cubic) ${\mathrm{CeO}}_{2}$ phase remains stable down to 4.8 nm and, as expected, does not undergo a transition to any of the other available structures with lower symmetry. \textcopyright{} 1996 The American Physical Society.

Reply to "Comment on 'Relation between copper L x-ray fluorescence and 2p x-ray photoelectron spectroscopies' "

Ohno's preceding Comment [Phys. Rev. B 52, 6127 (1995)] was based on experimental raw spectra of copper L x-ray emission. The Cu L x-ray emission spectra were, however, heavily smeared by the self-absorption effect, which was a source of contradiction. The electronic structure of divalent copper oxide was calculated placing one core hole and two 3d holes, with the result that the spectator 3d holes were delocalized in the adiabatic limit. This implies that the spectator 3d hole produced by the ${\mathit{L}}_{1,2}$${\mathit{L}}_{3}$${\mathit{M}}_{4,5}$ Coster-Kronig transition preceding the ${\mathit{L}}_{3}$-M x-ray emission will be mostly delocalized at the time of the ${\mathit{L}}_{3}$-M x-ray emission, and thus the spectator satellite will be weaker than is expected for the free atom. Ohno did not consider this delocalization, which was another source of contradiction.

Spin structures of tetragonal lamellar copper oxides.

The spin Hamiltonian of tetragonal lamellar antiferromagnets is shown to contain several novel anisotropies. Symmetry allows bond-dependent anisotropic exchange interactions, which lead to (a) interplane mean-field coupling and (b) an in-plane anisotropy which vanishes classically but arises from quantum zero point energy (QZPE). A similar QZPE involving the interplane isotropic interaction prefers collinear spins. Adding also diploar anisotropy, the competition between all these effects explains for the first time the spin structures of many cuprates.

Crystal structure and phase stability of the new metallic lanthanum strontium copper oxide

The structure of (La 1−xSr x) 4Cu 4O 10 (x=0.1429) has been reexamined by neutron powder diffraction techniques. The results confirm the structural model based on the X-ray powder diffraction data. The general structural features of this material are similar to those of the other three-dimensional oxygen-deficient perovskites BaLa 4Cu 5O 14− δ , (La 1−xSr x) 8Cu 8O 20− δ (0.16≤x≤0.24) and La 2Sr 6Cu 8O 18− δ ; in particular the oxygen vacancies in the basal plane are ordered along [001]. The framework of [Cu 4O 10] consists of one type of corner-shared CuO 5 groups. X-ray powder diffraction and thermal analysis investigations showed that the orthorhombic phase (La 1−xSr x) 4Cu 4O 10 (x=0.1429) is thermodynamically stable at low temperature (<500°C), although it can only be prepared above 1020°C in oxygen. The phase transition from orthorhombic (La 1−xSr x) 4Cu 4O 10 to tetragonal (La 1−xSr x) 8 Cu 8O 20 (x=0.1429) above 500°C is slow and occurs over a wide temperature range, characteristic of a second-order transition.

Crystal structure and Tc in copper oxides : A clue to the mechanism of high-temperature superconductivity

The critical temperature T c of cuprate superconductors has been mapped onto a Δ V M- d p plane where Δ V M is the difference between the Madelung site potential for a hole on a Cu site and that on an O site and d p is the Cu-O bond length within the CuO 2 plane. It is found that the materials with a larger Δ V M tend to have a smaller d p, and that T c increases either with the decrease of Δ V M or with the decrease of d p. These observations are discussed in terms of a local pair resonance model in which high- T c superconductivity is viewed as macroscopic resonance involving coherent motion of paired holes in real space. Structural features affecting T c are also discussed.

Copper Oxide Superconductors Through 1994

ABSTRACTThis paper briefly describes the chemistry and structures of known copper oxide superconductors as of November 1994. A tabulation of the unique, reliably superconducting cuprates is presented, with year of discovery, as is a simple classification scheme. Recent trends in new materials research are described.

The synthesis and structure of a new Bi-based copper oxide with (Bi, M)O monolayers: (Bi, M)Sr 2(R, Ce) 3Cu 2O 11−δ

A new layered cuprate, (Bi, M)Sr 2(R, Ce) 3Cu 2O 11−δ(M+Cd, Cu; R: rare earth elements) (Bi-based “1232”), has been synthesized. The structure of the compounds has been determined by the powder X-ray diffraction method. It is found that the cell parameters are approximately equal to a = 3.85 A ̊ and c = 17 A ̊ . Comparison of the calculated and observed diffraction intensities shows that the structures are similar to that of (TI, Cu)Sr 2(R, Ce) 3Cu 2O 11. The behavior of the resistivity dependence on temperature is directly related to that heat treatment.

Investigation of the crystal growth of CuO from the CuO-Bi2O3 system

The relationship between properties and structure in high-temperature superconducting copper oxides has stimulated the investigation on the properties of single crystal CuO. The phase diagram of CuO-CuBi2O4 has been established by improved thermogravimetric analysis (ITGA), differential thermal analysis (DTA) and X-ray diffraction. The crystallization temperature of CuO was determined by ITGA and the dependence of crystallization temperature on cooling rates showed about 20 °C supercooling in the crystal growth of CuO from the CuO-Bi2O3 system. Using the theory of crystal growth under stable state conditions, an initial kinetic analysis of seed crystal dissolution was also performed on the ITGA data. Using the phase diagram and the ITGA information, large crystals have been grown near the surface of the high-temperature solution or the bottom of the crucible by a combination of ITGA and the top-seeding method.

Structure and oxygen stoichiometry in complex neodymium strontium cobalt copper oxides: [NdSrCo 1−xCu xO 4−y

Compounds from the solid solution NdSrCo 1−xCu xO 4−y (0 <- x <- 0.9) have been prepared and characterised with powder X-Ray and neutron diffraction together with thermogravimetric analysis. The materials have been shown to adopt the K 2NiF 4 structure (spacegroup 14/mmm). Variations of the a- and c- parameters show a complex behaviour with increasing copper content. At all values of x, the average transition-metal oxidation is high. The changes in cell parameters are discussed in terms of oxygen stoichiometry and transition-metal oxidation state from the perspective of the Brown bond valence calculation theory.