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1.
Iron oxides, oxyhydroxydes and oxycarbonates derived from the layered Ruddlesden‐Popper (RP) structure form a large family of layered compounds. Besides the classical RP oxides Srn+1FenO3n+1, single intergrowths with the generic formulation (A,Sr)n+2FenO3n+2 and (A,Sr)n+3FenO3n+3 (A = Tl, Pb, Bi…) can be generated by increasing the multiplicity of the rock salt layers, and multiple intergrowths of these single intergrowths can be synthesized. Starting from oxygen deficient RP oxides such as n = 3 member Sr3NdFe3O9?δ, oxyhydroxydes hydrates and oxyhydroxydes such as Sr3NdFe3O7.5(OH)2·H2O and Sr3NdFe3O7.5(OH)2 can be created topotactically. Carbonate groups can also replace FeO6 octahedra in the n = 3 member Sr4Fe3O10, leading to layered oxycarbonates Sr4Fe3?x(CO3)xO10?4x with 0 < × ≤ 1. Shearing mechanism applied transversally to the layers allows collapsed structures to be generated such as the [Bi2Sr3Fe2O9]n [Bi4Sr6Fe2O16] family and the ferrite Bi13Ba2Sr25Fe13O66. Finally the replacement of rock salt SrO layers in the intergrowth Sr2FeO4 allows a new series of modulated structures [Sr8Fe12O26]·[Sr3Fe2O6]n to be generated, built up of layers of FeO5 bipyramids and tetragonal pyramids intergrown with perovskite layers.  相似文献   

2.
Ba(Zr,Ti)O3/LaNiO3 layered thin films have been synthesized by chemical solution deposition (CSD) using metal-organic precursor solutions. Ba(Zr,Ti)O3 thin films with smooth surface morphology and excellent dielectric properties were prepared on Pt/TiO x /SiO2/Si substrates by controlling the Zr/Ti ratios in Ba(Zr,Ti)O3. Chemically derived LaNiO3 thin films crystallized into the perovskite single phase and their conductivity was sufficiently high as a thin-film electrode. Ba(Zr,Ti)O3/LaNiO3 layered thin films of single phase perovskite were fabricated on SiO2/Si and fused silica substrates. The dielectric constant of a Ba(Zr0.2Ti0.8)O3 thin film prepared at 700°C on a LaNiO3/fused silica substrate was found to be approximately 830 with a dielectric loss of 5% at 1 kHz and room temperature. Although the Ba(Zr0.2Ti0.8)O3 thin film on the LaNiO3/fused silica substrate showed a smaller dielectric constant than the Ba(Zr0.2Ti0.8)O3 thin film on Pt/TiO x /SiO2/Si, small temperature dependence of dielectric constant was achieved over a wide temperature range. Furthermore, the fabrication of the Ba(Zr,Ti)O3/LaNiO3 films in alternate thin layers similar to a multilayer capacitor structure was performed by the same solution deposition process.  相似文献   

3.
Due to the extraordinary versatility of the perovskite structure in accommodating different dopant ions in its structure, in recent years a huge number of multifunctional perovskite materials have been developed. In this work we aim to obtain high temperature-stable and huge dielectric constant materials for supercapacitors by doping divalent Mg2+ and trivalent Sb3+ ions into the octahedral sites, and divalent Sr2+ ions into the dodecahedral sites of lead zirconate-titanate perovskite. The resulting (Pb0.95Sr0.05)(Zr0.425Ti0.45Mg0.042Sb0.083)O3-δ is examined by X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), dielectric spectroscopy (DS) and resonance dielectric spectroscopy (RDS) in order to correlate composition, local structure, ion valence and chemical environment of the doped material with the dielectric properties. HRTEM evidences that a composite structure, with co-existent ferroelectric domains and relaxor nanodomains, is formed by doping. XPS shows that Sb3+ and Mg2+ substitute for the Ti4+/Zr4+ ions, pointing to these strong defects as the main cause for the appearance of the relaxor phase. DS and RDS found that the ferroelectric lead zirconate-titanate transforms into a re-entrant relaxor-ferroelectric composite with a huge dielectric constant of about 104 which remains stable (within ±10%) in the high temperature range up to 250 °C, pointing to this mechanism of relaxor phase re-entrance below the normal ferroelectric phase transition, as being responsible for the enhancement.  相似文献   

4.
Phase relations have been investigated within the Sr5Nb4O15−SrTiO3−Sr4Nb2O9 region of the SrO−Nb2O5−TiO2 system with a view to clarifying the occurrence of fully oxidised perovskite related phases. Overall phase analysis was carried out by powder X-ray diffraction and microstructures were clarified by transmission electron microscopy. There is only one main composition triangle in this area at 1350°C. The tie-line between Sr5Nb4O15 and SrTiO3 contains a homologous series of hexagonal layered perovskite phases including Sr6Nb4TiO18 and Sr7Nb4Ti2O21. The phase Sr4Nb2O9 is a nonstoichiometric phase with a disordered perovskite structure. There is some extension of this phase along the Sr4Nb2O9−SrTiO3 tie-line, but SrTiO3 does not show a significant composition range. Samples with a composition Sr4Nb2O9, when heated at 900°C show several ordered modifications. Samples along the Sr4Nb2O9−SrTiO3 tie-line which are annealed at 900°C contain these ordered materials together with samples showing considerable short range order which increases as the Ti content increases.  相似文献   

5.
In order to investigate the factors determining the relative stabilities of layered perovskite and pyrochlore structures of transition metal oxides containing trivalent bismuth, several ternary and quaternary oxides have been investigated. While d0 cations stabilize the layered perovskite structure, cations containing partially-filled d orbitals (which suppress ferroelectric distortion of MO6 octahedra) seem to favor pyrochlore-related structures. Thus, the vanadium analogue of the layered perovskite Bi4Ti3O12 cannot be prepared; instead the composition consists of a mixture of pyrochlore-type Bi1.33V2O6, Bi2O3, and Bi metal. The distortion of Bi1.33V2O6 to orthorhombic symmetry is probably due to an ordering of anion vacancies in the pyrochlore structure. None of the other pyrochlores investigated, Bi2NbCrO7, Bi2NbFeO7, TlBiM2O7 (M = Nb, Ta), shows evidence for cation ordering in the X-Ray diffraction patterns, as indeed established by structure refinement of TlBiNb2O7.  相似文献   

6.
Qinghua Yin  Y. S. Lin 《Adsorption》2006,12(5-6):329-338
The paper reports on effect of doping Ag+, Ni2+, Ca2+, Ba2+ or Zr4+ in La0.1Sr0.9Co0.9Fe0.1O3−δ (LSCF1991) on its oxygen sorption capacity and desorption rate. The dopant can be incorporated into LSCF1991 matrix causing lattice expansion. The oxygen sorption capacity and tendency for the disordered perovskite to ordered brownmillerite phase transition for these samples decrease in the order: LSCF1991 > LSCF-Ag > LSCF-Ni > LSCF-Ca > LSCF-Ba > LSCF-Zr. The oxygen desorption rate also decreases in the same order for the doped samples. Doping increases the tendency of the disorder to order phase transition and enhances oxygen desorption rate during oxygen desorption step. Doping Ag and Ni provides more pronounced enhancement in oxygen desorption rate. The results suggest that Ag and Ni doped LSCF1991 samples are promising sorbents for use in a high temperature sorption process for air separation.  相似文献   

7.
The electrochemical performance of the layered perovskite YSr2Cu3−xCoxO7+δ, a potential solid oxide fuel cell (SOFC) cathode, is improved by increasing the Co content from x = 1.00 to a maximum of x = 1.30. Single phase samples with x > 1.00 are obtained by tuning the Y/Sr ratio, yielding the composition Y1−ySr2+yCu3−xCoxO7+δ (where y ≤ 0.05). The high temperature structure of Y0.95Sr2.05Cu1.7Co1.3O7+δ at 740 °C is characterised by powder neutron diffraction and the potential of this Co-enriched material as a SOFC cathode is investigated by combining AC impedance spectroscopy, four-probe DC conductivity and powder XRD measurements to determine its electrochemical properties along with its thermal stability and compatibility with a range of commercially available electrolytes. The material is shown to be compatible with doped ceria electrolytes at 900 °C.  相似文献   

8.
A series of Ba1-xSrxTi1-yZryO3 (0≤x≤0.5, 0≤y≤0.4) and BA1?xZnxTi1?ySnyO3 (0≤x≤0.3, 0≤y≤0.3) solid solutions were synthesized by low-temperature/low-pressure hydrothermal method below 170°C, 0.8 MPa. XRD pattern and cell parameters-composition figures of these prepared powders demonstrated that they are completely miscible solid solutions based on BaTiO3. Furthermore, TEM showed that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of those powders doped by Sr2+ and Zr4+ or Zn2+ and Sn4+ have dielectric constant twelve times higher than and dielectric loss 1/6 those of pure BaTiO3 phase at room temperature.  相似文献   

9.
Synthesis and Properties of the Layered Perovskite Phase Sr3Mo1.5Zn0.5O7‐δ The new layered perovskite phase Sr3Mo1.5Zn0.5O7‐δ was synthesized by solid state reaction using a Zn/ZnO oxygen buffer. The crystal structure was refined from X‐ray powder pattern by the Rietveld method. The compound crystallizes tetragonal in the space group I4/mmm (no. 139) with the lattice parameters a = 3.9631(3) Å, c = 20.583(1) Å. An oxygen deficiency corresponding to δ ≈ 0.25 was determinated, indicating the presence of molybdenum in mixed valence (Mo4+ and Mo6+).  相似文献   

10.
Summary The homogeneity of the distributions of doped V and Ti in Al2O3:V3+, Y3Al5O12:V3+, Al2O3:Ti3+, Y3Al5O12:Ti3+ single crystals was studied by means of laser emission microanalysis. The applied statistical methods include one-way variance analysis, two-way variance analysis, regression models and the gradient method.  相似文献   

11.
A series of Ba1-xSrxTi1-yZryO3 (0≤x≤0.5, 0≤y≤0.4) and BA1?xZnxTi1?ySnyO3 (0≤x≤0.3, 0≤y≤0.3) solid solutions were synthesized by low-temperature/low-pressure hydrothermal method below 170°C, 0.8 MPa. XRD pattern and cell parameters-composition figures of these prepared powders demonstrated that they are completely miscible solid solutions based on BaTiO3. Furthermore, TEM showed that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of those powders doped by Sr2+ and Zr4+ or Zn2+ and Sn4+ have dielectric constant twelve times higher than and dielectric loss 1/6 those of pure BaTiO3 phase at room temperature.  相似文献   

12.
A series of TiO2?CZrO2 supported V2O5 catalysts with vanadia loadings ranging from 4 to 12 wt% were synthesized by a wet impregnation technique and subjected to various thermal treatments at temperatures ranging from 773 to 1,073?K to understand the dispersion and thermal stability of the catalysts. The prepared catalysts were characterized by X-ray powder diffraction (XRD), BET surface area, oxygen uptake, and X-ray photoelectron spectroscopy (XPS) techniques. XRD results of 773?K calcined samples conferred an amorphous nature of the mixed oxide support and a highly dispersed form of vanadium oxide. Oxygen uptake measurements supported the formation of a monolayer of vanadium oxide over the thermally stable TiO2?CZrO2 support. The O 1s, Ti 2p, Zr 3d, and V 2p core level photoelectron peaks of TiO2?CZrO2 and V2O5/TiO2?CZrO2 catalysts are sensitive to the calcination temperature. No significant changes in the oxidation states of Ti4+ and Zr4+ were noted with increasing thermal treatments. Vanadium oxide stabilized as V4+ at lower temperatures, and the presence of V5+ is observed at 1,073?K. The synthesized catalysts were evaluated for selective oxidation of o-xylene under normal atmospheric pressure in the temperature range of 600?C708?K. The TiO2?CZrO2 support exhibits very less conversion of o-xylene, while 12 wt% V2O5 loaded sample exhibited a good conversion and a high product selectivity towards the desired product, phthalic anhydride.  相似文献   

13.
This paper describes the results of electron microscopy, high-temperature powder neutron diffraction, and impedance spectroscopy studies of brownmillerite-structured Ba2In2O5 and perovskite structured Ba(InxZr1−x)O3−x/2. The ambient temperature structure of Ba2In2O5 is found to adopt Icmm symmetry, with disorder of the tetrahedrally coordinated (In3+) ions of the type observed previously in Sr2Fe2O5. Ba2In2O5 undergoes a ∼6-fold increase in its ionic conductivity over the narrow temperature range from ∼1140 K to ∼1230 K, in broad agreement with previous studies. This transition corresponds to a change from the brownmillerite structure to a cubic perovskite arrangement with disordered anions. Electron microscopy investigations showed the presence of extended defects in all the crystals analyzed. Ba(InxZr1−x)O3−x/2 samples with x=0.1 to 0.9 adopt the cubic perovskite structure, with the lattice parameter increasing with x.  相似文献   

14.
New hybrid composites based on mesostructured V2O5 containing intercalated poly(ethylene oxide), poly-o-methoxyaniline and poly(ethylene oxide)/poly-o-methoxyaniline were prepared. The results suggest that the polymers were intercalated into the layers of the mesostructured V2O5. Electrochemical studies showed that the presence of both polymers in the mesostructured V2O5 (ternary hybrid) leads to an increase in total charge and stability after several cycles compared with binary hybrid composites. This fact makes this material a potential component as cathode for lithium ion intercalation and further, a promising candidate for applications in batteries.  相似文献   

15.
《Solid State Sciences》2007,9(7):564-573
High pressure and temperature are used to synthesise perovskite related phases in the Sr–Cr(IV)–O system. The n = 1, 2 and ∞ members of the Srn+1CrnO3n+1 family have been obtained. Another new member, n = 3 as well as an hexagonal layered perovskite have also been observed by transmission electron microscopy and electron diffraction. The average structure of Sr3Cr2O7 as determined by XRD has space group I4/mmm, whereas its microstructure includes a large amount of defects both in the layer stacking and within the layers. 2D magnetism and a large electrical resistance in Sr3Cr2O7 are observed as opposed to the nonlocalized electronic behaviour of SrCrO3.  相似文献   

16.
A. Manthiram 《Polyhedron》1985,4(6):967-970
Two series of vanadium spinels, viz.AV2O4 and A1.5O4(A = Mg, Mn and Zn) have been prepared at significantly lower temperatures (700–850 K) by hydrogen-reduction of the corresponding oxide precursors, AV2O6 and A2V2O7 respectively. The cation distribution in these phases have been determined by X-ray powder diffraction intensity analysis. The former vanadium(III) spinels have a cation distribution of (A2+)t[V23+]oO4 while the latter mixed-valence vanadium spinels have a distribution of (A2+)t[A0.52+V1.03+V0.54+]oO4.  相似文献   

17.
A series of Ba1-xSrxMyTi1-yO3 (M = Zr, Sn, 0?x?0.4, 0?y?0.3) solid solutions were synthesized with the soft chemical method below 100 °C. XRD pattern and cell parameters-composition figures of the prepared powder demonstrate that they are completely miscible solid solutions based on BaTiO3. Furthermore, TEM shows that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of the powder doped with Sr2+and Zr4+ or Sn4+ have dielectric constant eight times higher and dielectric loss thirty per cent lower than those of pure BaTiO3 phase at room temperature.  相似文献   

18.
AVO3 (A = Ba2+, Sr2+, La3+, Gd3+) oxides have been prepared by hydrogen reduction of suitable vanadium(V) ternary oxides. The oxidation state of vanadium in the reduction products seems to be controlled by the nature of other cations. In the presence of strongly basic alkaline-earth metal ions, Ba2+ and Sr2+ as in Ba2V2O7 and Sr2V2O7, vanadium is reduced to +4 state. But when A is a trivalent lanthanide ion as in LnVO4 (Ln = La or Gd), the reduction of vanadium proceeds to +3 state to yield LnVO3 phases. The products have been characterized by X-ray diffraction. BaVO3 crystallizes in a hexagonal structure related to Ba3V2O8 while SrVO3, LaVO3 and GdVO3 crystallize in GdFeO3 type structure. Electrical transport measurements indicate that BaVO3, LaVO3 and GdVO3 are p-type semiconductors while SrVO3 is metallic.  相似文献   

19.
The La0.7A0.3MnO3, La0.7A0.3Mn0.9Cr0.1O3 (A = Sr, Ba, Pb) polycrystalline perovskite manganites sample was prepared by the sol–gel technique. The replacement of partial Mn3+/Mn4+ by Cr3+ (Cr3+ with the same electronic configuration as Mn4+) cause the variety of magnetocaloric property and magnetic entropy change. The maximum magnetic entropy change ΔSH = −1.16 J/kg K and the Relative Cooling Power (about 43.3 J/kg) were obtained from La0.7Sr0.3Mn0.9Cr0.1O3 in the Cr3+ doped series under 1 T magnetic field variation. On this paper, Banerjee criteria had been remarked to distinguish the first-order or second-order phase transition on phase transition of the doped perovskite manganites.  相似文献   

20.
The electronic structures of some transition-metal ions doping the ferroelectric oxide BaTiO3 are calculated through the density functional theory framework (LCAO-LSD ADF method) on extended clusters [XO6Ba8Ti6] embedded in a punctual charge set depicting the crystalline environment. The transition ions X are Fen+(n = 2, 3, 4, 5), Ti3+, Nb4+, and Nb5+. Some related defects like Fe(SINGLE BOND)Vo, where Vo stands for a lacunar oxygen site, are also investigated through a similar process. The positions of impurity levels insides the O2p(SINGLE BOND)Ti3d band gap are obtained from eigenvalues and related optical transition or ionization energies are calculated using excited states. This allows us to discuss the photorefractive effect present in such doped materials. The EPR fine-structure parameters a and D are also derived for Fe3+ in cubic and tetragonal symmetries from crystal field calculations using parameters drawn from molecular orbital results. © 1997 John Wiley & Sons, Inc.  相似文献   

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