Crystal Structure of (Cr,Cu)(Sr,La)2(La,A)Cu2O8‐δ (1212‐type) and (Cr,Cu)Sr2(Y,Ce)2Cu2O10‐δ (1222‐type) Phases

Conditions of the synthesis, crystal structures, mechanical properties, electrical resistivities and magnetizations of cuprates with the general formula (Cr,Cu)(Sr,La)₂(La,A)Cu₂O_8‐δ where A=Ca or Sr of 1212‐type and (Cr,Cu)Sr₂(Y,Ce)₂Cu₂O_10‐δ of 1222‐type were investigated. The compositions of the cuprates and an amount of the impurity phases in the samples were determined. Rietveld refinement of the structure was carried out. It was found that the formal charges of Cu (FC_Cu) calculated from the electroneutrality of refined phase compositions do not achieve value optimal for the appearence of superconducting phases.     

The Particularities of Infinite‐Layer Compounds Sr1–xLnxCuO2–δ (Ln=La,Pr, Nd,Eu)

The superconducting phases with general formula Sr_1–xLn_xCuO_2–δ with Ln=La (Tc=24…40K); Pr (Tc=30…44 K); Nd (Tc=8K…40 K); Eu (Tc…40 K) and non‐superconducting phases of CaCuO₂– type structure were prepared by high‐pressure synthesis. The products were examined by X‐ray powder diffraction. For the determination of composition Rietveld method was used. Structure investigations have shown that non‐superconducting phases have oxygen vacancies. With in the Cu formal charge range from 1.81 to 1.93 the infinite layer cuprates exhibit superconductivity. Coexistence of both superconducting and non‐superconducting phases of the CaCuO₂–type structure in samples with Ln=Nd and Eu was found.     

The Phase Formation,Solid Solution Range and Substitution of La for Ba in La1+zBa2‐zCu3Oy

The phase formation, solid solution range and the substitution of La for Ba in La_1+zBa_2‐zCu₃O_y (La123) system are investigated systematically for obtaining and understanding the optimum condition to prepare La123 superconductors with higher Tc. The solid solution ranges of La_1+zBa_2‐zCu₃O_y are z=0.20‐0.70 in air and z=0 in N₂. Atmosphere of air or O₂ is favourable for the substitution of La for Ba. The substitution is suppressed when La_1+zBa_2‐zCu₃O_y are sintered and cooled in N₂ . It is found that sintering and cooling procedure in N₂ atmosphere is one key procedure to prepare single phase high‐quality LaBa₂Cu₃O_y superconductor with higher Tc.     

Crystal Structure Phase Transitions in the Perovskites A(Cu1−xMnx)Mn4O12(A = Na+, Ca2+, Y3+, La3+)

X-Ray diffraction and neutronographical studies on the crystal structure of the perovskitelike compounds A(Cu_1−xMn_x)Mn₄O₁₂ have been undertaken. It has been shown that the samples with 50% of Mn³⁺ in the octahedral sites have a cubic unit cell, while the samples with higher Mn³⁺ composition may have a monoclinic or rhombohedral unit cell. The temperature increase raises the symmetry to the cubic one. The concentration ranges with different symmetry type have been determined. The lowering of the symmetry of the unit cell is due to the cooperative Jahn-Teller effect.     

Growth,structure, and superconducting properties of Bi2Sr2Ca2Cu3O10 and (Bi,Pb)2Sr2Ca2Cu3O10‐y crystals

Large and high‐quality single crystals of both Pb‐free and Pb‐doped high temperature superconducting compounds (Bi_1‐xPb_x)₂Sr₂Ca₂Cu₃O_10‐y (x = 0 and 0.3) were grown by means of a newly developed “Vapour‐Assisted Travelling Floating Zone” technique (VA‐TSFZ). This modified zone‐melting technique was realised in an image furnace and allowed for the first time to grow Pb‐doped crystals by compensating for the Pb losses occurring at high temperature. Crystals up to 3×2×0.1 mm³ were successfully grown. Post‐annealing under high pressure of O₂ (up to 10 MPa at T = 500°C) was undertaken to enhance T_c and improve the homogeneity of the crystals. Structural characterisation was performed by single‐crystal X‐ray diffraction (XRD) and the structure of the 3‐layer Bi‐based superconducting compound was refined for the first time. Structure refinement showed an incommensurate superlattice in the Pb‐free crystals. The space group is orthorhombic, A2aa, with cell parameters a = 27.105(4) Å, b = 5.4133(6) Å and c = 37.009(7) Å. Superconducting studies were carried out by A.C. and D.C. magnetic measurements. Very sharp superconducting transitions were obtained in both kinds of crystals (ΔT_c ≤ 1 K). In optimally doped Pb‐free crystals, critical temperatures up to 111 K were measured. Magnetic critical current densities of 2�10⁵ A/cm² were measured at T = 30 K and μ₀H = 0 T. A weak second peak in the magnetisation loops was observed in the temperature range 40‐50 K above which the vortex lattice becomes entangled. We have measured a portion of the irreversibility line (0.1‐5 Tesla) and fitted the expression for the melting of a vortex glass in a 2D fluctuation regime to the experimental data. Measurements of the lower critical field allowed to obtain the dependence of the penetration depth on temperature: the linear dependence of λ(T) for T < 30 K is consistent with d‐wave superconductivity in Bi‐2223. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magneto‐transport properties of polycrystalline YBa2(Cu1‐xMx)3O7‐δ (M = B and Mn)

The magnetic and transport properties of polycrystalline YBa₂ (Cu_1‐xM_x)₃ O_7‐δ (M = B and Mn) superconductor was investigated. Samples of YBa₂(Cu_1‐xB_x)₃O_7‐δ doped with several concentrations of boron B(x = 0.05 and 0.1) were investigated using magnetization measurements. A YBa₂(Cu_1‐xMn_x)₃O_7‐δ sample doped with Mn with concentration of x = 0.02 was investigated using current‐voltage (I‐V) measurements. Our results on the YBa₂(Cu_1‐xB_x)₃O_7‐δ samples reveal a considerable increase in the hysterisis width of the magnetization, M versus the applied magnetic field H with increasing boron concentration. The lower critical field was also found to be enhanced by boron doping. The critical current density, J_c was found to be significantly enhanced in the Mn‐doped sample. The enhancement of J_c was found to be more significant at the lower temperatures for all applied magnetic fields used (0 Oe, 300 Oe, and 500 Oe). Thus, chemical doping is suggested to enhance the vortex pinning forces in the YBCO samples. From the resistivity (R‐T) measurements, chemical doping of the samples was found to have no significant effect on the critical temperature, T_c. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Crystal Structure of [La(NO3)6{Cu(2,2′-bipy)2}2][La(NO3)6Cu(2,2′-bipy)2]CH3CN with the Most Profuse Modes of Nitrate Coordination

The title compound [La(NO₃)₆{Cu(2,2′-bipy)₂}₂][La(NO₃)₆Cu(2,2′-bipy)₂] CH₃CN was synthesized, the crystal and molecular structures were determined at room temperature. The complex formed monoclinic crystals, space group P21/n (No.14), a = 10.354 (3) A, b = 23.440 (9) A, c = 32.817 (9) A, b = 90.39 (2)°, Z = 4. The crystal structure consisted of a discrete [La(NO₃)₆{Cu(2,2′-bipy)₂}₂]⁺ cation and [La(NO₃)₆Cu(2,2′-bipy)₂]^- anion and a non-coordinated CH₃CN molecule. Each La(III) ion was 12-coordinate with twelve oxygen atoms from six chelating nitrate ligands. There were four modes of nitrate coordination and the coordination geometry of all three copper ions was different in the crystal structure.     

Phase Formation,Crystal Structure and Electrical Properties of La212 Type Compound Substituted by Silver or Praseodymium

The La212 type compounds substituted by silver or praseodymium are prepared by solid state reaction method. It is found that compounds La_2‐xSr_xCa_0.5Pr_0.5Cu₂O₆, La_1.6Pr_0.4Ca_1‐xSr_xCu₂O₆ and La_2‐xPr_xCa_0.5Sr_0.5Cu₂O₆ can be formed for x=0.4‐1.1, 0‐0.5 and 0‐1.5, respectively. A new member of La212 type compounds, La_2‐xAg_xCaCu₂O₆ is also prepared. Their structures are verified by Rietveld structure refinement to belong to the structure type of La212 cuprate oxide with space group I4/mmm. Their electrical properties are investigated. La_1.65Ag_0.35CaCu₂O₆ displays metal‐like behavior and its resistivity decreases with the decrease of temperature from 300K to 4.2K.     

Orthorhombic — tetragonal phase transition and oxygen index of YBa2Cu3O6+δ

The orthorhombic — tetragonal phase transition of YBa₂Cu₃O_6+δ has been investigated by X-ray powder diffraction methods. The transition is of the second order or very close to second order and no coexistence of tetragonal and orthorhombic phases has been observed. The transition strongly depends on the oxygen index δ which changes with temperature. Typical patterns of the triplet 006, 020, and 002 obtained by precise X-ray powder diffraction measurements have been presented and shown to be useful for identification of YBa₂Cu₃O_6+δ and estimation of oxygen index δ.     

Second harmonic generation properties of Ca3(O3C3N3)2 ‐Sr3(O3C3N3)2 solid solutions

Solid solutions of the second harmonic generation (SHG) materials Ca₃(O₃C₃N₃)₂ (CCY) and Sr₃(O₃C₃N₃)₂ (SCY) were prepared via exothermic solid state metathesis reactions from appropriate amounts of the corresponding metal chlorides and potassium cyanate at 525 °C. The change in SHG intensity caused by the successive cation substitution is reported. Differential thermal analyses are used to explore the SCY–K(OCN) phase diagram as a medium for the growth of SCY crystals.     

Three‐Dimensional Structure Constructed via Hydrogen Bonds and π‐π Stacking Interaction. Crystal Structure of [Cu(AFO)2(H2O)2](ClO4)2.2(AFO).2H2O (AFO = 4,5‐Diazafluoren‐9‐one)

The structure of the title complexes [Cu(AFO)₂(H₂O)₂](ClO₄)₂.2(AFO).2H₂O (AFO = 4,5‐Diazafluoren‐9‐one)has been established by single‐crystal X‐ray diffraction. The complex crystallizes in the triclinic space group P‐1 with cell constants a = 7.659(3) Å, b = 11.066(3) Å, c = 14.203(5) Å, alpha = 75.16(3)°, β = 79.87(3)°, gamma = 85.71(3)°, Z = 1. The structure was solved by direct methods and refined to R₁ = 0.0595 (wR₂ = 0.1164). The X‐ray analysis reveals that a pair of AFO ligands chelate to a Cu(II) atom in an asymmetric fashion with one Cu‐N bond being much longer than the other, the Cu(II) atom is further coordinated by a pair of aqua ligands to form an elongated octahedral geometry. In the crystal of the complex, the mononuclear complex cations [Cu(AFO)₂(H₂O)₂]²⁺, uncoordinated AFO molecules, lattice water molecules and perchlorate anions are assembled into 3‐D structure via hydrogen bonds and π‐π stacking interaction.     

Growth and characterization of large La1‐xPbxMnO3+δ (x=0.32–0.35) crystals

Large crystals of La_0.63Pb_0.37Mn O_3+δ with small La(Pb)‐ deficiency of about 0.005‐0.01 at.% were grown by high temperature solution growth method. The structure of the grown crystals was determined as rhombohedral with R‐3 space group by single‐crystal X‐ray diffractometry. The surface morphology of the crystals and the exact chemical composition was examined by scanning electron microscopy and energy dispersive X‐ray analysis methods, respectively. The IR‐transmission spectrum reveals the presence of Mn³⁺O₆‐ and Mn⁴⁺O₆‐ octahedra in the lattice of La_0.63Pb_0.37Mn O_3+δ crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microwave dielectric properties of (1‐x)La(Mg0.5Sn0.5)O3‐x(Sr0.8Ca0.2)3Ti2O7 ceramic system with a near zero temperature coefficient of resonant frequency

In this study, the microwave dielectric properties of (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system prepared by the conventional solid‐state method have been investigated for application in mobile communication. It was found that the diffraction peaks of (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system shift to higher angles as x increases from 0.2 to 0.4. It was also found that the X‐ray diffraction patterns of the 0.8La(Mg_0.5Sn_0.5)O₃‐0.2(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramics exhibited no significant phase difference at different sintering temperatures. The average grain size of the (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system decreased from 6.4 to 4.3 μm as the value of x increased from 0.2 to 0.4 sintered at 1550 °C for 4 h. The dielectric constant increased from 26.6 to 35.9 and the quality factor (Q×f) decreased from 31,600 to 23,300 GHz for (1‐x)La(Mg_0.5Sn_0.5)O₃‐x(Sr_0.8Ca_0.2)₃Ti₂O₇ ceramic system as the x value increases from 0.2 to 0.4 sintered at 1550 °C for 4 h. The average value of temperature coefficient of resonant frequency (τ_f) increased from ‐18 to +8 ppm/ K as the x value increases from 0.2 to 0.4. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Double Salt Formation in the Cu(HCOO)2–Sr(HCOO)2–H2O System

The solubility in the Cu(HCOO)₂–Sr(HCOO)₂–H₂O system has been studied by the method of physico-chemical analysis at 25 and 50 °C. It has been established that two double salts are formed in the system: CuSr₂(HCOO)₆ · H₂O at 25 °C and CuSr(HCOO)₄ · 4 H₂O at 50 °C. The latter salt has not yet been described in the literature. It has been characterized by X-ray powder diffraction and DT and TG analysis. CuSr(HCOO)₄ · 4 H₂O crystallizes in the triclinic system with lattice parameters a = 12.376(6) Å, b = 13.394(4) Å, c = 11.508(6) Å, α = 93.38(3)°, β = 94.01(3)°, γ = 75.04(3)°. Dehydration proceeds in two stages.     

The struvite‐type compounds M [Mg(H2O)6](X O4), where M = Rb,Tl and X = P,As

Phases with composition M [Mg(H₂O)₆](X O₄), where M = Rb, Tl and X = P, As, were obtained by means of the gelatine‐gel diffusion technique from Mg‐EDTA and corresponding metal phosphate/arsenate solutions at pH > 9. The crystal structures were determined from single crystal X‐ray diffractometer data sets. All compounds crystallize isotypically with two formula units in the orthorhombic struvite [NH₄[Mg(H₂O)₆](PO₄)] structure type in space group Pmn 2₁ and with lattice parameters of a ≈ 6.88, b ≈ 6.16, c ≈ 11.34 Å. The structures consist of slightly distorted [Mg(OH₂)₆] octahedra (m symmetry), X O₄ tetrahedra (m symmetry) and [M O₁₀] polyhedra (m symmetry) as single building units, held together by an intricate hydrogen bonding network. The structure can also be described as made up of closed packed pseudo ‐hexagonal layers of [Mg(OH₂)₆] units stacked along [010] with the X O₄ tetrahedra and the M atoms in the voids of this arrangement. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal Growth and Spectroscopic Characterisation of BiB3O6:RE3+ (RE3+ = Pr3+, Nd3+, Gd3+, Er3+, Tm3+)

Large single crystals of optical quality of BiB₃O₆:RE³⁺ (RE³⁺ = Pr³⁺, Nd³⁺, Gd³⁺, Er³⁺, Tm³⁺) were grown from nearly stoichiometric melts using the top‐seeding growth technique to dimensions up to 12 x 12 x 18 mm³. Absorption spectra were measured in the wavelength range from 10000 cm^‐1 to 30000 cm^‐1 with an absorption spectrometer to estimate the doping concentration of RE³⁺. For the determination of the phonon energies and the quenching behaviour of the host lattice IR and Raman spectra were recorded.     

Synthesis and structure of zirconium and 3d-transition metal phosphates M 0.5Zr2(PO4)3(M = Mn, Co, Ni, Cu, Zn)

Double zirconium and 3d-transition metal phosphates of the compositions M 0.5Zr2(PO4)3[M = Mn (I), Co (II), Ni (III), Cu (IV), Zn (V)] have been synthesized and the types of their structures have been refined. Compounds I, II, III, IV, and V are all monoclinic (sp. gr. P2₁/n, Z = 4) and have the unit cell parameters a = 12.390(3), 12.389(3), 12.385(3), 12.389(3), 12.389(2) Å; b = 8.931(4), 8.928(3), 8.924(4), 8.925(4), 8.929(3) Å; c = 8.843(3), 8.840(2), 8.840(3), 8.841(3), 8.842(2) Å, β = 90.55(1), 90.54(1), 90.53(1), 90.53(1), 90.54(1)°; V = 978.5, 977.7, 977.0, 977.4, 978.1 ų, respectively. All the structures have the {[Zr₂(PO₄)₃]^?}3_∞-type frameworks. The crystallographic data for 3d-transition and alkali earth metal phosphates described by the general formula M _0.5Zr₂(PO₄)₃ are compared.     

A3BGa3Si2O14(A=Ca,Sr;B=Nb,Ta)晶体研究进展

介绍了一类性能优异、结构有序的新型材料--A3BGa3Si2O14(A=Ca,Sr;B=Nb,Ta)单晶,总结了其研究进展,并对该类晶体的生长、结构、热学、光学和压电性能进行了描述.     

Liquid Phase Epitaxy (LPE) of YB2Cu3O7-δ High Tc Superconductors

YBa₂Cu₃O_7-δ films were grown by liquid phase epitaxy in Y-ZrO₂ crucibles on (110)NdGaO₃ substrates. A change in the preferred crystallographic growth direction was observed reproducibly. The growth mode changes from pure c-axis oriented over mixed c/a-axis oriented films to pure a-axis oriented films with increasing undercooling. X-ray diffraction measurements and atomic force microscopy investigations with c-axis oriented as well as a-axis oriented films are presented. It will be shown that atomically smooth steps with 0.2-0.8 μM width can be achieved by LPE, which are free from melt remnants. Furthermore the values for the enthalpy of dissolution from literature, which are varying in a wide range, will be combined and a new value will be calculated in terms of a multi particle model.