Cu-O Bond Length Research Articles

Ｌｎ２ＣｕＳｎＯ６（Ｌｎ＝Ｌａ，Ｐｒ，Ｎｄ，Ｓｍ）の高圧合成

La2CuSnO6, even though it contains CuO2 layers, does not exhibit superconductivity. It might result from the in-plain Cu-O bond length being too long(about 2.0 A, compared with 1.9 A of La2CuO4). So, we replaced La with smaller atoms Pr, Nd, Sm, expecting that these might contract the CuO2 layers and lead to superconductivity. For synthesis we used high pressure(6Gpa for Pr, Nd and 8Gpa for Sm). The result Is that, contrary to our wish, the CuO2 layers buckled even more seriously and the Cu-O bond did not get shorter. In this paper, we focused on the magnetism of Ln2CuSnO6(Ln=La, Pr, Nd). In the temperature range of 150 to 350K, these compounds showed almost the same characteristics which have been explained assuming spin-canted weak ferromagnetism. However, Pr2CuSnO6and Nd2CuSnO6exhibited ferromagnetic behavior at lower temperature suggesting ordering of the Pr3+(Nd3+)moments. Antlferromagnetic coupling between the weak ferromagnetic CuO2 layers and the ferromagnetic LnO layers has also been suggested.

CNDO studies of Y-Ba-Cu-O superconductors V. Co/Cu substitution

Electronic properties of [ConCu3−nO12]−17 and [Ba8ConCu3−nO12]−1 model clusters (n=0–3) are investigated using CNDO molecular orbital method. Our results well reproduce the trends of experimental data on Cu-O bond lengths and supposed negative charge transfer from central Cu(1)O chains to lateral Cu(2)O2 planes with increasing Co content.

Tetrakis[μ-(3-bromobenzoato)-μ-(2-dimethylaminoethanolato)-copper(II)

A cubane-type Cu 4 O 4 core has been found in the title tetrameric copper(II) complex {tetrakis(μ-3-bromobenzoato)-1κO: 2κO'; 2κO: 3 κO'; 3 κO: 4κO';-4κO:1κO'-tetrakis[μ-2-(dimethylamino)ethanolato] -1κN,1:2:3κ 3 O;2κN,2:3:4κ 3 O;3κN,3:4:1κ 3 O;4κN,4:1:2κ 3 O-tetracopper(II), [Cu 4 (C 7 H 4 BrO 2 ) 4 (C 4 H 10 NO) 4 ]}. The short Cu-O ethanolato bonds form an eight-membered ring folded in a boat-like conformation. The Cu...Cu distances vary between 3.121(2) and 3.796(3)A. Each Cu atom has a distorted octahedral environment. Two ethanolato O atoms, a carboxy O atom and an amino N atom form the equatorial coordination plane, with Cu-O bond lengths in the range 1.914(12)-1.954(14)A and Cu-N bond lengths in the range 2.011(12)-2.057 (13)A. The axial sites are occupied by an ethanolato O atom and an O atom of the carboxylate group, with Cu-O distances in the range 2.443 (8)-2.877 (9) A.

Tetrakis(dimethyl sulfoxide-O)copper(II) Bis(perchlorate)

The four dimethyl sulfoxide ligands of the title complex, [Cu(C2H6OS)4]2+.2ClO4−, adopt a tetrahedrally distorted square-planar arrangement around the central CuII ion, with all Cu-O bond lengths falling within the range 1.934 (6)–1.954 (6) Å. One O atom from each of the perchlorate anions interacts weakly at distances of 2.466 (8) and 2.640 (8) Å.

Effective Hamiltonian for high- Tc ceramics, (…)CU mO n− x

A new perspective on the Animalu nonlocal pairing model of high- T c superconductivity is reported, currently stressing the possible interband (Cu3d-02p) charge transfer matrix ( t). The mean-field Suhl-Matthias-Walker-type Hamiltonian obtained reveals hybrid and nonhybrid Cooper-pair wavefunctions, the latter manifesting anomalous splitting of quasiparticle energy. This result, presently interpreted as the Jahn-Teller (JT) effect, is briefly discussed in the context of data on the Cu-O bond length. In our brief Green's function analysis, an approximate t-dependence of the nonlocal pair potential ( V ij , i ≠ j) and a semi-empirical expression for the JT stabilisation energy (E JT ), which we believe to be new, are presented. Numerical estimates of E JT for YBa 2Cu 3O 6.9 compare well with photoemission data. Normal state energies obtained in the model are in excellent qualitative or quantitative agreement with the Mott-Hubbard picture, results from the Gutzwiller approximation of the Emery model and Ohkawa's breathing mode scheme for the copper ceramic oxides.

Temperature Dependence of the Crystal Structure and EPR Spectrum of Bis(1,3,5-Trihydroxycyclohexane)copper(II) Tosylate. A Unified Interpretation Using a Model of Dynamic Vibronic Coupling.

The crystal structure of bis(1,3,5-trihydroxycyclohexane)copper(II) tosylate is reported at temperatures of 293, 233, 188, 163, and 93 K, as are the structures of the Zn(II) and Ni(II) analogues at room temperature for comparison. The isomorphous compounds are triclinic, space group P&onemacr;, with one formula unit in the unit cell. The unit cell parameters of the Cu compound at 293 K are a = 6.456(5) Å, b = 9.505(3) Å, c = 12.544(3) Å, alpha = 76.57(2) degrees, beta = 87.48(4) degrees, gamma = 76.65(4) degrees. The centrosymmetric ZnO(6) and NiO(6) octahedra are tetragonally compressed with a slight orthorhombic distortion. The Cu(2+) polyhedra exhibit similar geometries, but with considerably larger deviations from a regular octahedron. Two of the three independent Cu-O bond lengths and two of the g-values change significantly as a function of temperature. A model of dynamic vibronic coupling is presented which explains both the EPR and structural data. Vibronic wave functions associated with a Jahn-Teller potential energy surface modified by an orthorhombic lattice "strain" are given. The temperature dependence of the structures is calculated from the nuclear parts and that of the g-values from the electronic parts of the wave functions. The temperature dependence of the structures and g-values is also interpreted using a simpler model involving an equilibrium between two forms of the complex which differ solely in their orientation in the crystal lattice, and the results of the two approaches are compared.

Catena-Poly[aqua(benzimidazole-N3)copper(II)-μ-malonato-O,O'':O'

The title compound forms a polymeric chain, [Cu(C 3 H 2 O 4 )(C 7 H 6 N 2 )(H 2 O)]∞. A malonate ion adopts a bridging position between two Cu atoms, coordinating via three of its O atoms. Two form a six-membered chelate ring, the third coordinates to the neighbouring Cu atom. The square-pyramidal Cu II coordination comprises one N and three O atoms as the base, and an H 2 O molecule in the apical position. The equalization of C-O bonds of both carboxylate groups and a differentiation of Cu-O bond lengths is observed.

Non-adiabatic electron-lattice interactions in the copper-oxide superconductors

Transport measurements distinguish the superconductive phase from the parent antiferromagnetic and the overdoped metallic phases in La2−xSrxCuO4. For small x, holes in the CuO2 sheets form non-adiabatic polarons containing, experimentally, five Cu atoms. Within a polaron, a first-order contraction of the mean Cu-O bond length collapses the Hubbard U and transfers spectral weight from the Hubbard bands to the gap between them. In the superconductive phase above Tc, condensation into a polaron liquid produces an ɛ(k) dispersion curve, and dynamic pseudo Jahn-Teller deformations within the polaron give a Seebeck enhancement with Tmax≈140 K. The polarons order pair-wise into 〈110〉 stripes alternating with parent-phase stripes; below Tc, the stripes are perfectly ordered. In the overdoped phase, the parent phase is squeezed out; the vibronic states become homogeneous.

Redox mechanism for the generation of holes in TlBa1-xSrxLaCuO5+ delta : A neutron-diffraction study.

Our neutron-diffraction study of the single Tl-O layered TlBa{sub 1{minus}{ital x}}Sr{sub {ital x}}LaCuO{sub 5+{delta}} system ({ital x}=0.0, 0.4, 0.7, and 1.0) shows that the in-plane Cu-O(2) bond length decreases monotonically with increase of {ital x}. This is consistent with the introduction of holes in CuO{sub 2} layers or the appearance of superconductivity in the sample with {ital x}=0.4 ({ital T}{sub {ital c}}=22 K) and increase of {ital T}{sub {ital c}} with {ital x}, {ital T}{sub {ital c}}=25 and 30 K for samples with {ital x}=0.7 and 1.0, respectively. Further, the valence of copper, derived from Cu-O bond length, increases with increase of {ital x} despite the fact that the O content decreases as {ital x} increases. This clearly suggests that the internal redox mechanism due to the overlap of the empty Tl 6{ital s} band with the filled Cu 3{ital d}{sub {ital x}}{sup 2}{minus}{ital y}{sup 2} band is responsible for the generation of holes, and therefore superconductivity, in these materials.

Comparative Studies on Periodatocuprate(II, III) and Telluratocuprate(II, III)

The crystal structures, electronic spectra, and Cu2 p XPS of Cu(III) complexes Na 4H[Cu(H 2TeO 6) 2] · 17H 2O and Na 4K[Cu (HIO 6) 2] · 12H2O have been described. The characterizations of a Cu(III) atom in a complex are as follows: (i) In a square-planar coordination, the average bond length of Cu-O is 0.183 nm, shorter than the 0.190-0.200 nm found for a Cu(II) complex. (2) The "blue shift" occurs for d-d transitions in the electronic spectrum of the Cu(III) complex compared to those of its related Cu(II) complex, resulting from the higher valence state. (3) Cu(III) compounds with CuO 4 square-planar coordination are expected to be diamagnetic whereas Cu(II) compounds to be paramagnetic. (4) Comprehensive investigations on Cu2 p XPS show that the binding energy of Cu2 p 3/2 of a pure Cu(III) compound is about 2.0 eV higher than that of its corresponding Cu(II) compound: the shakeup satellites do not appear in the Cu2 p XPS for a pure diamagnetic Cu(III) compound, the same as found for a diamagnetic Ni(II) compound: the FWHM of the signal of Cu2 p XPS may become broader for Cu(III) compound because its core hole's lifetime shortens due to the higher valence state of copper.

Rietveld Refinement of YBa2Cu3-xNixOy Prepared by Quenching and Oxygen Gettering

We have refined the structures for YBa2Cu2.94Nio.O6Oy (2% Ni) and YBa2Cu2.8ONio.20Oy (6.67% Ni) at y ∼ 6.95 and y ∼ 6.5 contents. Oxygen was reduced by two independent methods: quenching from 690 °C and oxygen gettering at 450 OC, Cu-O bond lengths were calculated based on Rietveld structure refinements for the various samples; they indicate the likely occupancy of Ni in the plane (Cu2) site of the 123 superconductor.

Relationship between Madelung Potentials and Bond Valence Sums in Copper-Oxide Superconductors

High-T c copper-oxide superconductors are characterized from the viewpoint of crystal chemistry through comparative analyses of Cu-O bond lengths, Madelung site potentials and bond valence sums. The interrelationships among these structural and electronic parameters are investigated in detail for the elucidation of the crystal-chemical factors governing T c and the species of doped carriers. Two characteristics, the strain parameter for CuO2 planes calculated on the basis of bond valence sums and the Madelung-potential difference between in-plane O and Cu sites, are shown to represent an essentially equivalent physical content. The ability of the present analysis to predict the maximum value of T c of (possible candidates for) cuprate superconductors is also discussed.

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.

Synthesis and spectral and structural characterization of a bridging chloropicolinatocopper(II) complex, Cu(C5H4NCOO)Cl

The title complex of copper(II) chloride with picolinic acid was prepared and characterized by spectroscopic and X-ray crystallographic methods. The complex, Cu(C5H4NCOO)Cl, crystallizes tetragonal, space group P42/n (No. 86),a=976.4(1),c=1499.6(4) pm,N=8;Rw=0.048 for 543 observed MoKα diffractometer data. In the structure of the complex two μ-chloro bridges form only slightly bent Cu2Cl2 rings [Cu-Cl=224.2(4) and 275.6(4) pm] with Cu...Cu separation of 359.4(2) pm and Cl...Cl separation of 348.7(5) pm. These edge-sharing copper coordination polyhedra are further linked via the N and O donor atoms of the picolinato anions at Cu-N distances of 199.6(12) pm and Cu-O bond lengths of 195.7(8) and 200.6(10) pm, to form a two-dimensional layer structure in which these layers are arranged along theab plane. Each picolinate anion functions as a tetra-dentate ligand: N(1) and O(2) are coordinated to the same Cu(II) center whereas O(1) is bonded to a neighbouring Cu(II) center. O(2) is further bonded to the latter Cu(II) center at a long Cu-O distance of 256.5(8) pm. The electronic, infrared and Raman spectra of the solid complex are reported and discussed.

Crystal structure and charge localization in Pb 2Sr 2Y 1− xCa xCu 3O 8 for x = 0.0–0.5

Neutron powder diffraction studies of Pb 2Sr 2Y 1- x Ca xCu 3O 8 samples for x = 0.0-0.5 have shown that Ca doping causes a positive charge transfer to the CuO 2 as well as to the PbO layers. The bond-valency sum for the Cu ions in the CuO 2 layer increases as a function of x, while the bond-valency sum for the Pb ions increases up to x = 0.4 and is then saturated. The axial Cu-O bond length shows a maximum at x = 0.4, and the shortest axial Cu-O bond length was found for x = 0.5. The x = 0.5 sample was found to become superconducting with an onset temperature of 79 K. The distance between the Cu ions in the CuO 2-(Y, Ca)-CuO 2 sandwich is increased by 0.14 Å by going from x = 0.0 to 0.5.

Crystal structure and superconductivity of La2− xBaxCuO4 (0.03≤ x≤0.24)

High-resolution neutron powder diffraction has been performed to investigate the crystal structure of La 2− x Ba x CuO 4 as a function of x(0.03≤ x≤0.24). The crystal parameters at 115 K refined by profile analysis show that the Cu-planar O(1) bond lengths decrease by 0.008 Å when x is increased by 0.1. This result indicates that the overlap of Cu and planar O orbitals, and thus the charge transfer, increases with x. The length of the Cu-apical O(2) bonds decreases at a rate of about one half of that for Cu-O(1), suggesting that the apical oxygens O(2) also play an important role in the charge transfer process. The changes of the Cu-O(1) bond lengths of the compound with x=0.125 at 15 K are further studied in connection with the structural phase transition to the low-temperature tetragonal (LTT) phase. These results are discussed in terms of their implication for the electronic structure and superconductivity of this system.

Temperature dependence of the local structure in superconducting and non-superconducting Tl 2Ba 2CuO y studied by extended x-ray absorption fine structure

The local structure of Tl 2Ba 2CuO y (Tl2201) has been investigated by extended X-ray absorption fine structure (EXAFS) on the Cu K-edge. The result for the high- T c sample with T c =70 K indicates a splitting of Cu-O bondlengths in the CuO 2 plane, which shows a strong temperature dependence over a wide temperature range well above T c, although the crystallographical symmetry of the unit cell is tetragonal. The splitting is evaluated from the filtered EXAFS by the beat-node method, and the maximum splitting distance is ≁0.16 Å. The magnitude of the splitting abruptly decreases in the vicinity of T c by more than 10%. On the other hand, no splitting in the in-plane Cu-O bondlengths was observed in non-superconductor samples from room temperature down to 30 K. No apparent change of axial oxygen sites was observed. These facts strongly demonstrate that the local structural distortion in the CuO 2 plane may directly relate to the superconductivity.

The synthesis and characterization of a new family of single layer cuprates LnBaCuO2BO3 (Ln=La, Pr, Nd, Sm, Eu and Gd)

We have succeeded in preparing a new series of cuprate compounds with the composition of LnBaCuO2BO3 where Ln = La, Pr, Nd, Sm, Eu and Gd. As indicated by the X-ray powder (diffraction patterns and IR spectra, the structure of the compounds is built up by [CuO2] planes and borate layers containing distinct BO3 groups. The in-plane Cu-O bond lengths were found to decrease from 1.971 Å to 1.936 Å when the ionic radii of the rare earth elements (from Ln=La to Ln=Gd) are decreased. Such a variation is equivalent to that found in the n-type superconducting Ln2CuO4 compounds of the T'-structure. Although the LnBaCuO2BO3 compounds possess the common feature of most high-Tc cuprates, we have failed in inducing superconductivity in this system yet.

Effects of substitution for Cu in CuO2 planes with dopants of different electron configuration in YBa2Cu3O7

The effects of substitution for copper in the system YBa2Cu3-xMxO7-y, with M=Ni, Zn and Ni12/Zn12/, and 0<or=x<or=0.5, have been studied with respect to its superconducting transition temperature, hole concentration, electronic transport properties in the normal state and structure parameters. The results strongly indicate that the band filling, the excess of holes, and electron localization due to the destruction of the integrity of the CuO2 planes are not the predominant factors for the suppression of Tc in the case of substitution for Cu(2). Semi-quantitative analyses reveal that the Zn and Ni ions act as impurity scattering centres with a radius of scattering cross larger than the average Cu-O bond length of the CuO2 planes, which directly destroys the superconducting path in CuO2 planes and decreases the superconducting energy gap. This may be the main reason for the suppression of superconductivity.

Strain and proximity effect in (La,Sr)2CuO4 based superconducting superlattices.

Controlled variations of the in-plane Cu-O bond length and interlayer proximity coupling have been produced in laser-ablated superlattices containing superconducting ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$ (LSCO). In LSCO/${\mathrm{Sm}}_{2}$${\mathrm{CuO}}_{4}$ strained superlattices, the in-plane lattice constant a of the LSCO layers is increased and the transition temperature (${\mathit{T}}_{\mathit{c}}$) is decreased. We estimate the effective pressure to be -8 GPa by comparing with LSCO/${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ unstrained superlattices. We conclude the in-plane Cu-O bond length is an important factor controlling ${\mathit{T}}_{\mathit{c}}$. For LSCO/overdoped-${\mathrm{La}}_{1.65}$${\mathrm{Sr}}_{0.35}$${\mathrm{CuO}}_{4}$ (metallic) superlattices, a proximity-induced coherence length of 50 \AA{} is calculated for the overdoped material using the de Gennes--Werthamer theory, from the ${\mathit{T}}_{\mathit{c}}$ dependence on individual layer thickness.