Synthesis and characterization of self-assembled c-axis oriented Bi2Sr3Co2O(y) thin films by the sol-gel method

Bi(2)Sr(3)Co(2)O(y) thin films are prepared on SrTiO(3) (100), (110) and (111) single crystal substrates using the sol-gel method. All the thin films are c-axis oriented regardless of the orientation of the substrate suggesting self-assembled c-axis orientation, and X-ray photoelectron spectroscopy results give evidence of coexistence of Co(3+) and Co(2+) ions in the derived films. Transmission electronic microscopy observations reveal that all samples are c-axis oriented with no obvious differences for different samples, and the c-axis lattice constant is determined as ~15 ? suggesting the misfit structure. A phenomenological thermodynamic phase diagram for self-assembled c-axis orientation is established for misfit cobaltate-based films using chemical solution deposition. All samples behave like semiconductors due to the coexistence of Co(3+)/Co(2+) ions, and the resistivity at 350 K is ~47, 39 and 17 mΩ cm for the thin films on SrTiO(3) (100), (110) and (111), respectively, whereas the Seebeck coefficient at 300 K is 97, 89 and 77 μV K(-1). The successful attainment of Bi(2)Sr(3)Co(2)O(y) thin films with self-assembled c-axis orientation will provide an effective prototype for investigation of growth mechanisms in complex oxide thin films with a misfit structure.     

Formation of SrSnO3 shell-like inclusions in the Bi2Sr2CaCu2O8+x superconductor via chemical reaction

Superconducting composites Bi-2212–SrSnO₃ have been prepared by reacting between the Bi–Sr–Ca–Cu–O precursor and Sr₂SnO₄ or Ca₂SnO₄ at 800–950°C, followed by crystallisation of Bi-2212 from the partial melt at decreasing temperature. The samples have been characterised by powder X-ray diffraction, scanning electron microscopy and magnetic measurements. The materials consist of large Bi-2212 lamellae and complex-shaped fine inclusions of SrSnO₃. The composite obtained using Sr₂SnO₄ contains almost all the SrSnO₃ phase in the form of micron-sized spherical shells, which are partly included in Bi-2212 lamellae, partly agglomerated in-between. The shells are perforated, thus allowing the Bi-2212 crystals to grow through them. It has been found that the shell-like grains form at an early stage of the precursor thermal treatment between 800 and 850°C. A mechanism of the SrSnO₃ shell formation is proposed. The composites exhibit T_c in the range of 82–87 K and reveal up to five times better magnetic flux pinning at T≥30 K in comparison with the undoped Bi-2212 sample prepared using the same experimental procedure.     

Transformations de la phase supraconductrice a hauteT c (Bi,Pb)2Sr2CaCu2O8+x

DTA-DTG systematic study of highT _c superconducting phase (Bi,Pb)₂Sr₂CaCu₂O_8+x, with and without lead, shows a quantitatively opposite variation of oxygen stoechiometry on heating and cooling. Multiplate sample container, designed for the study, allowed to dissociated PbO loss from oxygen variations. Phases transformations have been studied under severalP _O2 by scanning DTA and DTG. Oxygen variations evolution has been evaluated by isothermal TG. The results proved that phase diagram representation must take into consideration theP _O2 coordinate.     

Accurate Determination of the Electronic Structure Parameters of the Spin Ladder Compounds SrCu2O3, Sr2Cu3O5 and CaCu2O3

Ab initio embedded cluster calculations have been employed to calculate a large number of electronic structure parameters of three different spin ladders, namely SrCu₂O₃, CaCu₂O₃ and Sr₂Cu₃O₅. Using the iterative difference dedicated configuration interaction methodology, magnetic couplings J and hopping amplitudes t are determined for first to fourth nearest neighbors. In addition, the four-body cyclic exchange J _ring is extracted and the direct exchange K, the neutral-ionic hopping integral t ₀ and the on-site repulsion U are calculated for first and second nearest neighbor copper ions. The substitution of these parameters in the pertubative superexchange relation J=2K−4t ₀²/U yields magnetic coupling parameters in close agreement with the variational estimates. The spin ladders can be considered as an interpolation between the one-dimensional (1D) spin chains and the 2D antiferromagnets. Hence, results are compared with similar parameters in the spin chain Sr₂CuO₃ and the two-dimensional antiferromagnet La₂CuO₄.     

Characterization of electronic transition energies and trigonal distortion of the (FeO6)9- coordination complex in the Al2O3:Fe3+ system: a simple method for transition-metal ions in a trigonal ligand field

A theoretical method for studying the inter-relationships between electronic and molecular structure has been proposed on the basis of the complete energy matrices of electron-electron repulsion, the ligand field, and the spin-orbit coupling for the d5 configuration ion in a trigonal ligand field. As an application, the local distortion structure and temperature dependence of zero-field splitting for Fe3+ ions in the Al2O3:Fe3+ system have been investigated. Our results indicate that the local lattice structure of the (FeO6)(9-) octahedron in the Al2O3:Fe3+ system has an elongated distortion and the value of distortion is associated with the temperature. The elongated distortion may be attributed to the facts that the Fe3+ ion has an obviously larger ionic radius than the Al3+ ion and the Fe3+ ion will push the two oxygen triangles upward and downward, respectively, along the 3-fold axis. By diagonalizing the complete energy matrices, we found that the theoretical results of electronic transition energies and EPR spectra for Fe3+ ions in the Al2O3:Fe3+ system are in good agreement with the experimental findings. Moreover, to understand the detailed physical and chemical properties of the Al2O3, the theoretical values of the zero-field splitting parameters and the corresponding distortion parameters in the range 50 K 相似文献   

Synergistic effect of crystal and electronic structures on the visible-light-driven photocatalytic performances of Bi(2)O(3) polymorphs

Three polymorphs of Bi(2)O(3) were selectively synthesized via solution-based methods. The phase structures of the as-prepared samples were confirmed by X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). UV-vis diffuse reflectance spectroscopy was employed to study the optical properties of Bi(2)O(3) polymorphs, and the band gaps were estimated to be 2.80, 2.48, and 3.01 eV for α-Bi(2)O(3), β-Bi(2)O(3), and δ-Bi(2)O(3), respectively. The photocatalytic performances of the oxides were investigated by decomposing methyl orange and 4-chlorophenol under visible irradiation at room temperature. It was observed that β-Bi(2)O(3) displayed much higher photocatalytic performance than N-doped P25. Among the three polymorphs of Bi(2)O(3), the photocatalytic activities followed the order: β-Bi(2)O(3) > α-Bi(2)O(3) > δ-Bi(2)O(3), which was in good accordance with the photoluminescence spectra measurement results. The synergistic effect of the crystal and electronic structures on the photocatalytic performances of Bi(2)O(3) polymorphs was investigated. The much better photocatalytic activity of β-Bi(2)O(3) was considered to be closely related to its smaller band gap, higher crystallinity and unique tunnel structure.     

Electronic structures of superconductors YBa2Cu3−x M x O y (M=Sn,Ni)

Based on the EHMO approach, the energy band structures for superconductors YBa₂Cu_3–x Sn _x O _y (y>7) and YBa₂Cu_3–x Ni _x O_y (y<7) were calulated in the present paper. The influence of the cation doping at the Cu site in the unit cell and the oxygen content on their electronic structures was studied. The results showed that the cation doping at the Cu site resulted in the great decreases in the bandwidths of the broad anisotropic Cu-O bands and the densities of states. In YBa₂Cu_3–x Sn _x O _y , however, these decreases are compensated by the increase in the oxygen content caused by the Sn-doping, which results in a small change in the total densities of states. For YBa₂Cu_3–x Ni _x O _y , the effect of the doping on its electronic structures in dominant. The Ni-doping, therefore, results in a great change in the electronic structures. In addition, the study on the projected densities of states of the Ni-doped system revealed that the 2D Cu-O planes in the Y-Ba-Cu-O system played a dominant role in superconductivity.     

Crystal and electronic structure of Ni3Bi2S2 (parkerite)

The crystal structure of parkerite, Ni₃Bi₂S₂, was studied by single-crystal X-ray diffraction analysis and refined. The single crystal was prepared by the method of chemical transport reactions. The electronic structure of Ni₃Bi₂S₂ was calculated by the extended Hückel and DFT--LMTO--ASA methods. Substantial delocalization of electrons in the vicinity of the Fermi level and the presence of the strong Ni--S and Ni--Bi bonds were revealed. The Ni--Ni bonds are weak, which is in agreement with the X-ray diffraction data.     

Spectroscopic properties of Er(3+)/Yb(3+) co-doped Bi(2)O(3)-B(2)O(3)-GeO(2) glasses

Er(3+)/Yb(3+) co-doped 60Bi(2)O(3)-(40 - x)B(2)O(3)-xGeO(2) (BBG; x=0, 5, 10, 15 mol%) glasses that are suitable for fiber lasers, amplifiers have been fabricated and characterized. The absorption spectra, emission spectra, and lifetime of the (4)I(13/2) level and quantum efficiency of Er(3+):(4)I(13/2) --> (4)I(15/2) transition were measured and calculated. With the substitution of GeO(2) for B(2)O(3), both Delta lambda(eff) and sigma(e) decrease from 75 to 71 nm and 9.88 to 8.12 x 10(-21) cm(2), respectively. The measured lifetime of the (4)I(13/2) level and quantum efficiency of Er(3+):(4)I(13/2) --> (4)I(15/2) transition increase from 1.18 to 1.5 ms and 36.2% to 43.2%, respectively. The emission spectra of Er(3+):(4)I(13/2) --> (4)I(15/2) transition was also analyzed using a peak-fit routine, and an equivalent four-level system was proposed to estimate the stark splitting for the (4)I(15/2) and (4)I(13/2) levels of Er(3+) in the BBG glasses. The results indicate that the (4)I(13/2) --> (4)I(15/2) emission of Er(3+) can be exhibit a considerable broadening due to a significant enhance the peak A, and D emission.     

The structure of the framework strontium aluminate Sr6[Al12O24]·Bi2O3 with an included Bi2O3 “molecule”

We have determined the crystal structure of the aluminate Sr₆[Al₁₂O₂₄]·Bi₂O₃ obtained as a side phase in the Bi?Ca?Sr?Cu?O system as a result of its interaction with theAl₂O₃ crucible material. The aluminate has a trigonal unit cell with a=17.720, c=7.107 Å, V=1933 ų, space group R?3, Z=3. Experimental data were obtained on a RED-4 diffractometer (λMoK_α, 509 F_hkl, R=0.052, d_calc=4.38 g/cm³). In the framework of AlO₄ tetrahedra, we have isolated a 12-atomic block of a new 3-6-3 type as a secondary building unit (SBU). The block consists of a corrugated sixfold ring and six triple rings. The blocks are stacked according to the rhombohedral law to form elongated sixfold and eightfold rings. A distinctive feature of the structure is the presence of a trigonal-bipyramidal “molecular” Bi₂O₃ group not observed before. Its structural genetic role in the formation of this framework compound of the clathrate type is considered. For Sr aluminate, a corrected formula with a similar structure described in literature is proposed, namely, 6SrAl₂O₄·NaSr(OH)₃, but not 6SrAl₂O₄·1.5Sr(OH)₂.     

Thermal synthesis and properties of the (Bi2O3)1–x(Ho2O3)x pigments

The synthesis of new compounds based on the Bi₂O₃–Ho₂O₃ system, which can be used as new ecological inorganic pigments, is investigated in our laboratory. The optimum conditions for the syntheses of these compounds have been followed by the methods of thermal analysis that can provide first information about the temperature region of the pigment formation. The synthesis of these compounds was followed by thermal analysis using STA 449/C Jupiter (Netzsch, Germany).     

Structure and Luminescence Characteristics of Europium Activated Strontium Silicates Sr（Eu ,Bi）SiO3 and Sr（Eu ,Bi）2SiO4

Sr2SiO4 ： Eu^3 , Bi^3 and SrSiO3 ：Eu^3 , Bi^3 samples were synthesized at high temperature and high pressure. The effect of high pressure on the structure and luminescence properties of the samples were stud-ied. As a comparison, the samples were also prepared by the method of sol-gel at high temperature and atmo-spheric pressure. The SrSiO3 ： Eu^3 , Bi^3 prepared at atmosphere has a hexagonal phase structure; in the pressure range of 2. 34—4. 10 GPa, it is transformed into a pseudo-orthorhombic structure (monoclinic), and in the pressure range of 4. 10—4. 15 GPa, the structure change of Sr2SiO4 ： Eu^3 , Bi^3 has not been ob-served, it maintains the monoclinic structure of the samples synthesized at an atmospheric pressure. High pressure makes the luminescence properties of the samples changed obviously. The intensity and the relative quantum luminescent efficiency decrease, the half-width increases obviously and the red shift occurs. The changes of the luminescence properties result from the pressure-induced changes of the crystal structures.     

Photoelectron spectroscopy and density functional theory study of TiAlO(y) (-) (y=1-3) and TiAl(2)O(y) (-) (y=2-3) clusters

Small titanium-aluminum oxide clusters, TiAlO(y) (-) (y=1-3) and TiAl(2)O(y) (-) (y=2-3), were studied by using anion photoelectron spectroscopy. The adiabatic detachment energies of TiAlO(y) (-) (y=1-3) were estimated to be 1.11±0.05, 1.70±0.08, and 2.47±0.08eV based on their photoelectron spectra; those of TiAl(2)O(2) (-) and TiAl(2)O(3) (-) were estimated to be 1.17±0.08 and 2.2±0.1eV, respectively. The structures of these clusters were determined by comparison of density functional calculations with the experimental results. The structure of TiAlO(-) is nearly linear with the O atom in the middle. That of TiAlO(2) (-) is a kite-shaped structure. TiAlO(3) (-) has a kite-shaped TiAlO(2) unit with the third O atom attaching to the Ti atom. TiAl(2)O(2) (-) has two nearly degenerate Al-O-Ti-O-Al chain structures that can be considered as cis and trans forms. TiAl(2)O(3) (-) has two low-lying isomers, kite structure and book structure. The structures of these clusters indicate that the Ti atom tends to bind to more O atoms.     

Interaction in the system Bi(NO3)3-K3HCit-(H2O + glycerol)

The interaction in the system Bi(NO₃)₃-K₃HCit-(H₂O + glycerol) was studied by chemical analysis and pH titration over a wide range of ratios between the initial components. Solid phases of the compositions Bi(OH)_3?3x HCit _x · nH₂O and KBiCit · H₂O were isolated and investigated by X-ray powder diffraction and differential thermal analyses and IR spectroscopy. The effect of the chemical nature of the alkali metal on the solubility in the system under consideration was demonstrated.     

Synthesis of Bi2O3 and Bi4(SiO4)3 Thin Films by the Sol-Gel Method

Bi2O3 thin films were prepared by dipping silica slides in ethanolic solutions of tris(2,2-6,6-tetramethylheptane-3, 5-dionato)bismuth(III) [Bi(dpm)3] [1] and heating in air at temperatures 500°C. Bi4(SiO4)3 homogeneous thin films were obtained from the reaction of the bismuth oxide coating with the silica glass substrate at temperatures higher than 700°C. For heat treatments at temperatures between 600°C and 700°C, Bi2SiO5 coatings were obtained. The composition and microstructure evolution of the films were determined by Secondary Ion-Mass Spectrometry (SIMS), X-Ray Photoelectron Spectroscopy (XPS) and Glancing Angle X-Ray Diffraction (GA-XRD). The synthesis procedure was reproducible and allowed the control of the Bi2O3 phase composition. Moreover, the thin film annealing parameters were correlated with the formation of bismuth silicates, among which Bi4(SiO4)3 (BSO) is very appealing for the production of fast light-output scintillators [2].