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1.
An electron diffraction and microscopy study of the CaFexMn1−xO3−y system treated at 1100°C in air has been performed. An increase of y is accompanied by an increase of the cubic perovskite substructure parameter, the nonstoichiometry being accommodated in several ways. The system contains two solid solutions of the perovskite-type (P) and of the brownmillerite-type (B) and also an intermediate phase (x = 0.6) which makes disordered intergrowth with the B-type solid solution. These results are discussed in terms of multitwinning, randomly dispersed oxygen deficiency, and ordered and disordered intergrowth formation.  相似文献   

2.
Subsolidus phase ratios in the Na2MoO4-NiMoO4-Sc2(MoO4)3 system have been studied using X-ray diffraction, differential thermal analysis, and vibrational spectroscopy. A phase of variable composition Na1 ? x Ni1 ? x Sc1 + x (MoO4)3 (0 ≤ x ≤ 0.5) having NASICON structure (space group \(R\bar 3c\) ) and a triple molybdate crystallizing in triclinic system (space group \(P\bar 1\) ) have been obtained. The high conductivity of Na1 ? x Ni1 ? x Sc1 + x (MoO4)3 allows the phase of variable composition to be regarded as a promising sodiumion-conductive solid electrolyte.  相似文献   

3.
Solid solution phases Li2+x(LixMg1−xSn3)O8: 0 ≤ x ≤ 0.5 and Li2Mg1−xFe2xSn3−xO8: 0 ≤ x ≤ 1, both with ramsdellite type structure, have been synthesized by solid state reaction at 1773 and 1523 K, respectively. The relationship of the ramsdellite structure to the recently illustrated, tetragonal-packed structure is given. The Li2+x(LixMg1−xSn3)O8 solid solutions exhibit conductivities 4 × 10−6–5 × 10−4 (Ω cm)−1 at 573 K and corresponding activation energies, 0.93−0.74 eV. The highest conductivity was observed for Li2.3(Li0.3Mg0.7Sn3)O8, x = 0.3. In the solid solution series Li2Mg1−xFe2xSn3−xO8, the highest conductivity was exhibited by Li2Fe2Sn2O8, 2 × 10−5 (Ω cm)−1 at 573 K.  相似文献   

4.
Subsolidus phase ratios of the Na2MoO4-CoMoO4-Sc2(MoO4)3 system have been studied by X-ray diffraction, differential thermal analysis, and vibrational spectroscopy. A phase of variable composition Na1 ? x Co1 ? x Sc1 + x (MoO4)3, 0 ≤ x ≤ 0.5 having NASICON structure (space group \(R\bar 3c\) ) and triple molybdate NaCo3Sc(MoO4)5 crystallizing in triclinic system (space group \(P\bar 1\) ) have been obtained. The high conductivity of Na1 ? x Co1 ? x Sc1 + x (MoO4)3 allows the phase of variable composition to be regarded as a promising sodium-ion conducting solid electrolyte.  相似文献   

5.
Lithium cobalt oxide, LiCoO2, has been the most widely used cathode material in commercial lithium ion batteries. Nevertheless, cobalt has economic and environmental problems that leave the door open to exploit alternative cathode materials, among which LiNi x CoyMn1 − x − y O2 may have improved performances, such as thermal stability, due to the synergistic effect of the three ions. Recently, intensive effort has been directed towards the development of LiNi x Co y Mn1 − x − y O2 as a possible replacement for LiCoO2. Recent advances in layered LiNi x CoyMn1 − x − y O2 cathode materials are summarized in this paper. The preparation and the performance are reviewed, and the future promising cathode materials are also prospected.  相似文献   

6.
Young’s modulus, strain–stress behavior, fracture strength, and fracture toughness of (0≤×≤1) materials have been investigated in the temperature range 20–1,000°C. Young’s moduli of and , measured by resonant ultrasound spectroscopy, were 130±1 and 133±3 GPa, respectively. The nonlinear stress–strain relationship observed by four-point bending at room temperature was inferred as a signature of ferroelastic behavior of the materials. Above the ferroelastic to paraelastic transition temperature, the materials showed elastic behavior, but due to high-temperature creep, a nonelastic respond reappeared above ∼800°C. The room temperature fracture strength measured by four-point bending was in the range 107–128 MPa. The corresponding fracture toughness of , measured by single edge V-notch beam method, was 1.16±0.12 MPa·m1/2. The measured fracture strength and fracture toughness were observed to increase with increasing temperature. The fracture mode changed from intragranular at low temperature to intergranular at high temperature. Tensile stress gradient at the surface of the materials caused by a frozen-in gradient in the oxygen content during cooling was proposed to explain the low ambient temperature fracture strength and toughness.  相似文献   

7.
The paper presents a thermodynamic analysis of the formation of equilibrium defects in perovskitelike La1?x SrxCo1?y MeyO3?δ oxides, where Me = Cu or Mn, x = 0.0 or 0.3, and y = 0.0, 0.25, or 0.3, at high temperatures (873 K ≤ T ≤ 1373 K) depending on the composition and oxygen pressure (10?8 atm ≤ $p_{O_2 } $ ≤ 1 atm). The results were used to study the nature of charge transfer. Small-radius polarons were shown to be responsible for the electric properties of the cobaltites under consideration; their concentrations and mobilities were calculated.  相似文献   

8.
Calcium- and strontium-containing lanthanum orthoferrites have been studied using magnetic dilution method. It has been shown that the iron-atom clusters with competing ferro- and antiferromagnetic exchange interactions can exist. By using Mossbauer spectroscopy, Fe(IV) atoms have been found in the La1?0.33x Ca0.33x FexAl1?x O3 solid solutions and Fe(III) atoms in two different surroundings have been found in the La1?0.33x Sr0.33x Fe x Al1?x O3 solid solutions. The compositions of paramagnetic clusters stable at the infinite dilution have been proposed basing of the magnetic susceptibility and Mossbauer spectroscopy data.  相似文献   

9.
Perovskite-structure oxides La1?x Sr x FeO3?y (x = 0, 0.2, 0.6, 1) were synthesized by the mechanochemical method. In order to refine the stoichiometric composition and the charge state of ions, these samples were studied by X-ray photoelectron spectroscopy (XPS). An investigation of perovskites with x = 0, 0.2, and 0.6 in air at room temperature showed that these samples do not contain oxygen vacancies (y = 0), i.e., they are fully oxidized. Hence, to produce electrical neutrality, these samples should contain iron(4+) cations in an amount proportional to the degree of substitution (x) of strontium(2+) for lanthanum(3+). However, no Fe4+ cations were found in the oxides. All perovskites contain only Fe3+ cations, oxygen ions O2? along with oxygen ions with reduced electron density (O?). These data provid evidence of the possible electron density redistribution from oxygen ions to iron cations. The fact that the oxides contain oxygen ions with reduced electron density suggests that weakly bound lattice oxygen in substituted perovskites is represented by O? ions.  相似文献   

10.
We have used electron–positron annihilation to study superconducting cuprates Sm1+x Ba2–x Cu3O y . We have determined the average radii for oxygen ions in Sm1+x Ba2–x Cu3O y . Taking into account the ion coordinates and their radii, we have constructed a geometric model for the arrangement of copper and oxygen ions in CuO2 layers in the [b, c] plane, responsible for the superconductivity. From these data, we have determined the length of the ionic/covalent bonds and the width of the interionic gaps. We have established the effect of the features of the atomic structure of Sm1+x Ba2–x Cu3O y on the superconducting transition temperature T c and we have shown that T c increases as X inceases.  相似文献   

11.
In this work we present the synthesis and characterization of four compositions of the solid solution with the general formula Na2Zr x Ti6−x O13 (0≤x≤1) which was prepared by a sol-gel method. The main goal of this work is to evaluate the influence of the incorporation of different amounts of zirconium into the binary phase Na2Ti6O13 on two properties: the textural surface and E g values. This titanate phase crystallizes in a monoclinic unit cell and is built into an octahedral TiO6 framework forming a rectangular tunnel structure. Additionally, we have compared their photocatalytic performances in degradation of organic dyes under visible light. The heat-treated sol-gel samples were characterized by X-ray powder diffraction, N2 physisorption, thermal analysis, UV and FT-IR spectroscopy. According to the X-ray powder diffraction results, the new ternary tunnel compound Na2ZrTi5O13 was obtained as a single phase at 800°C. The cell parameters for the two end-member phases of that solid solution were refined to confirm that Zr ion was incorporated into the structural framework. This ternary compound had an E g value of about 2.9 eV. The activity of all heat-treated Na2ZrTi5O13 samples was tested in the photocatalytic degradation of methylene blue and Rhodamine B under visible light. The Na2ZrTi5O13 calcined at 400°C showed the best performance with 95% of photodegradation of methylene blue and a half time t 1/2 of 15 min.  相似文献   

12.
It is shown that in the processes of oxidation, reduction, and annealing of samples of the title, three-dimensional microdomains (3D-μD) play a predominant role. These microdomains are intergrown in the three dimensions and allow compositional variations in a very subtile manner. The existence of microdomains seems to be associated with the presence of tetravalent cations and with the fact that all the structures observed are superstructures of the perovskite cell.  相似文献   

13.
Quasi-one-dimensional (1D) solid solutions Ti1 ? x Fe x (OCH2CH2O)2 ? x/2 (0 < x ≤ 0.1) with the structure of anatase were prepared by heating the glycolate Ti1 ? x Fe x (OCH2CH2O)2 ? x/2 in an atmosphere of air at a temperature of >450°C. The conditions of formation and the properties of the new glycolate Ti3Fe2(OCH2CH2O)9 were described. It was found that the synthesized Ti1 ? x Fe x O2 ? 2x/2 solid solutions exhibit photocatalytic activity in the reaction of hydroquinone oxidation in an aqueous solution on irradiation with UV light. A correlation between the rate of oxidation of hydroquinone and the concentration of iron in the catalyst was established. A procedure for the preparation of titanium dioxide with the structure of anatase doped with iron and carbon (Ti1 ? x Fe x O(2 ? x/2) ? yCy) and also composites on its basis, which contain an excess amount of carbon, was proposed.  相似文献   

14.
Studies on the electrochemical behaviour of Ni1− x Cu x Co2O4 (x ≤ 0.75) and NiCo2− y Cu y O4 (y ≤ 0.30) electrodes in 5 mol dm−3 KOH aqueous solutions are presented. The oxide layers have been prepared by thermal decomposition of aqueous nitrate solutions on nickel supports at 623 K. Powder samples were also prepared by thermal decomposition under the same conditions. The powder samples and the oxide layers were characterised by X-ray powder diffraction. The influence of the copper content on the voltammetric response of the electrodes and activity towards oxygen evolution reaction is analysed and correlated with the surface composition of the electrodes by means of X-ray photoelectron spectroscopy data. The analysis of the results reveals that the presence of Cu affects the electrode behaviour and its influence depends on which cation has been replaced. Received: 22 February 1999 / Accepted: 26 October 1999  相似文献   

15.
Results are presented of an extended study on the induced lattice defects and their effects on the degradation of Si1−x Ge x devices, subjected to a 20 MeV alpha-ray, 1 MeV electron, 1 MeV fast neutron, and 20 and 86 MeV proton irradiations. The degradation of the electrical device performance increase with increasing fluence, while it decreases with increasing germanium content. In the Si1−x Ge x epitaxial layers, electron capture levels associated with an interstitial-substitutional boron complex are induced. The radiation source dependence of performance degradation is attributed to the difference of mass and the probability of nuclear collision for the formation of lattice defects.  相似文献   

16.
The sol-gel synthesis of Sr-doped-LaMnO3 thin film was investigated. The optimum condition was obtained when strontium, lanthanum and manganese nitrates were used as raw materials and diethylene or propylene glycol was used as solvent. An alumina plate was used as a substrate. The film thickness was about 0.2 m for one dip coating. The conductivity of Sr-substituted-LaMnO3 increased with increasing Sr content and showed ferromagnetic properties. The conduction mechanism was a hopping conduction due to the small polaron. The metal-semiconductor transition at around room temperature was considered to be caused by the Jahn-Teller effect.  相似文献   

17.
Mn4+ doped and Dy3+, Tm3+ co-doped MgAl2Si2O8-based phosphors were prepared by conventional solid state reaction at 1,300 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors, which showed broad red emission bands in the range of 600–715 nm and had a different maximum intensity when activated by UV illumination, was discussed. Such a red emission can be attributed to the 2E → 4A2 transitions of Mn4+.  相似文献   

18.
《Solid State Sciences》2004,6(10):1139-1148
The electronic structures of NiO, Ni0.875O, NiO0.875, Ni0.875Li0.125O, Ni0.875Li0.125O0.875 and Ni0.75Li0.25O0.875 with a NaCl-type crystal structure have been calculated using the ab initio linear muffin-tin orbitals method in the LSDA+U approximation. The effect of vacancies in the metal and metalloid sublattices and lithium ions on parameters of the NiO electronic spectrum (the energy gap and the valence band widths, etc.) has been analyzed. It is shown that the defects like the dipole LiVO and the tripole LiVOLi impaired stability and could reduce electrical conductivity of the nickel–oxide-based phases.  相似文献   

19.
In the present study high-temperature X-ray diffraction, thermal analysis, and mass-spectrometry have been employed for investigation of samples in the La1?x Sr x FeO3?δ family (0 ≤ x ≤ 1), the materials being solid solutions having perovskite structure. It has been shown that the loss of oxygen by the samples on heating to 1200°C in air (0 ≤ x ≤ 1) or in vacuum (x < 0.75) does not result in structural rearrangement of the solid solutions, but causes an increase in the lattice parameters. Heating of the compositions with x ≥ 0.75 in vacuum affords phases with ordered vacancies. The observed structural evolutions (growth of the unit cell parameter and vacancy ordering) are reversible, and on re-oxidation (on cooling in air or additional heating of the “vacuum” samples in air atmosphere) the original parameters of the oxides are recovered. The amount of oxygen evolved on heating increases in vacuum or in helium atmosphere, as compared to air, and also grows with rising strontium content, but under experimental conditions does not reach the maximum possible value (δ = x/2).  相似文献   

20.
Single crystals of the new phase Ba5Ru2−xAl1+x−yCuyO11 (x=0.378, y=0.085) have been grown from a powder mixture of BaCO3, RuO2 and CuO in an alumina crucible. The new compound crystallizes isostructurally to Ba5Ir2AlO11. The crystal structure was determined by X-ray single-crystal diffraction technique and refined to a composition of Ba5Ru1.622(8)Al1.29(1)Cu0.085(6)O11 (orthorhombic, Pnma (No. 62), a=18.615(4) Å, b=5.771(1) Å, c=11.098(2) Å, Z=4, R1=0.048, wR2=0.075). The composition of the new compound obtained from crystal structure refinement is in good agreement with the result of electron probe microanalysis using wavelength-dispersive X-ray spectroscopy. Octahedra [RuO6] are connected via faces forming pairs. The central positions of the octahedra pairs are statistically occupied by Ru and Al atoms. These octahedra pairs are interconnected to one-dimensional chains extending along [010] via tetrahedra [Al1−yCuyO4]. Isotypic Ba5Ru1.5Al1.5O11 is a further member of the solid solution with the lattice parameters a=18.6654(5) Å, b=5.7736(1) Å, c=11.0693(3) Å according to Rietveld refinement on a microcrystalline sample.  相似文献   

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