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1.
The partial energies and entropies of O2in perovskite-type oxides La0.6Sr0.4Co1−yFeyO3−δ(y=0, 0.1, 0.25, 0.4, 0.6) were determined as a function of nonstoichiometryδby coulometric titration of oxygen in the temperature range 650–950°C. An absolute reference value ofδwas obtained by thermogravimetry in air. The nonstoichiometry at a given oxygen pressure and temperature decreases with iron contenty. At low nonstoichiometries the oxygen chemical potential decreases withδ. The observed behavior can be interpreted by assuming random distribution of oxygen vacancies, an electronic structure with both localized donor states on Fe, and a partially filled itinerant electron band, of which the density of states at the Fermi level scales with the Co content. The energy of the Fe states is close to the energy at the Fermi level in the conduction band. The observed trends of the thermodynamic quantities can be interpreted in terms of the itinerant electron model only when the iron content is small. At high values ofδthe chemical potential of O2becomes constant, indicating partial decomposition of the perovskite phase. The maximum value ofδat which the compositions are single-phase increases with temperature. 相似文献
2.
Ian D. Fawcett Gabriel M. Veith Martha Greenblatt Mark Croft Israel Nowik 《Solid State Sciences》2000,2(8)
The SrMn1−xFexO3−δ (x=1/3, 1/2, 2/3) phases have been prepared and are shown by powder X-ray and neutron (for x=1/2) diffraction to adopt an ideal cubic perovskite structure with a disordered distribution of transition-metal cations over the six-coordinate B-site. Due to synthesis in air, the phases are oxygen deficient and formally contain both Fe3+ and Fe4+. Magnetic susceptibility data show an antiferromagnetic transition at 180 and 140 K for x=1/3 and 1/2, respectively and a spin-glass transition at 5, 25, 45 K for x=1/3, 1/2 and 2/3, respectively. The magnetic properties are explained in terms of super-exchange interactions between Mn4+, Fe(4+δ)+ and Fe(3+)+. The XAS results for the Mn-sites in these compounds indicate small Mn-valence changes, however, the Mn-pre-edge spectra indicate increased localization of the Mn-eg orbitals with Fe substitution. The Mössbauer results show the distinct two-site Fe(3+)+/Fe(4+δ)+ disproportionation in the Mn- substituted materials with strong covalency effects at both sites. This disproportionation is a very concrete reflection of a localization of the Fe-d states due to the Mn-substitution. 相似文献
3.
The space group symmetry and crystal structure of Tl3SbS3−xSex compounds in the composition range 0 < x < 3 have been determined by a combination of powder X-ray diffraction, electron diffraction, and high-resolution electron microscopy. The incongruently melting compound Tl3SbSe3 has been shown to crystallize in cubic space group P213 with a = 9.435Å in a structure related to that of Langbeinite. The convergent beam electron diffraction pattern of Tl3SbS3 is in accord with the space group R3m determined by X-ray diffraction. The cubic Langbeinite-type structure is found for Tl3SbS3−xSex for 0.5 < x < 3 and for Tl3SbyAs1−ySe3 for 0.077 < y < 1.0. A five-component compound Tl3Sb0.5As0.5Se1.5S1.5 was also found to be cubic. 相似文献
4.
The bulk superconducting YCa2Cu3O7−δ compounds are prepared at an ordinary pressure of oxygen by conventional solid-state reaction method. The formation of sample is tested by means of XRD and is studied for their ac susceptibility below room temperature up to 77.5 K. The samples are found single-phase orthorhombic structure and found superconducting at 83.5 K. It is shown that the analysis is consistent with published data on YBa2Cu3O7−δ oxide superconductor. 相似文献
5.
For La1−xThxNbO4+x/2, three phases with broad homogeneity regions occur, for 0.075 ≤ x ≤ 0.37, 0.41 < x < 0.61, and 0.65 ≤ x ≤ 0.74. All are related to the scheelite structure type, with at least the first exhibiting an incommensurate structural modulation. An analogous structurally modulated phase was found for LaNb1−xWxO4+x/2 for 0.11 ≤ x ≤ 0.22. Additional phases occur at La0.2Th0.8NbO4.4 and LaNb0.4W0.6O4.3. The electrical conductivity and the direction and wavelength of the structural modulation have been characterized for the La1−xThxNbO4+x/2 phase with 0.075 ≤ x ≤ 0.37. 相似文献
6.
Crystal structure, redox, and magnetic properties for the Pr1−xSrxFeO3−δ solid-solution phase have been studied. Oxidized samples (prepared in air at 900°C) crystallize in the GdFeO3-type structure for 0≤x≤0.80, and probably in the Sr8Fe8O23-type (unpublished) structure for x=0.90. Reduced samples (containing virtually only Fe3+) crystallize as the perovskite aristotype for x=0.50 and 0.67 with randomly distributed vacancies. The Fe4+ content increases linearly in the oxidized samples up to x≈0.70, whereupon it stabilizes at around 55%. Antiferromagnetic ordering of the G type is observed for oxidized samples (0≤x≤0.90) which show decreasing Néel temperature and ordered magnetic moment with increasing x, while the Néel temperature is nearly constant at 700 K for reduced samples. Electronic transitions for iron from an average-valence state via charge-separated to disproportionated states are proposed from anomalies in magnetic susceptibility curves in the temperature ranges 500–600 K and 150–185 K. 相似文献
7.
Yang-Su Han Shin-Hei Choi Jae-Up Jang Dong-Kuk Kim 《Journal of solid state chemistry》2001,160(2):435
Nanosized Fe2O3 clusters are pillared in the interlayer spaces of layered perovskites, H1−xLaxCa2−xNb3O10 (0≤x≤0.75) by a guest-exchange reaction using the trinuclear acetato-hydroxo iron cation, [Fe3(OCOCH3)7 OH·2H2O]+. The interlayer spaces of niobate layers are pre-expanded with n-butylammonium cations (n-C4H9NH+3), which are subsequently replaced by bulky iron pillaring species to form Fe(III) complex intercalated layer niobates. Upon heating at 380°C, the interlayered acetato-hydroxo iron complexes are converted into Fe2O3 nanoclusters with a thickness of ca. 3.5 Å irrespective of the interlayer charge density (x). The band-gap energy of the Fe2O3 pillars (Eg2.25 eV) is slightly larger than that of bulk Fe2O3 (Eg2.20 eV) but is smaller than that expected for such a small-sized semiconductor, which can be assigned to the pancake-shaped Fe2O3 pillars of 3.5 Å in height with comparatively large lateral dimension. X-ray absorption spectroscopic measurements at the Fe K-edge are carried out in order to obtain structural information on the Fe2O3 pillars stabilized between the niobate layers. XANES analysis reveals that the interlayer FeO6 octahedra have coordination environments similar to that of bulk α-Fe2O3, but noncentrosymmetric distortion of interlayered FeO6 is enhanced due to the asymmetric electric potential exerted by the negatively charged niobate layers. Scanning electron microscopic observation and nitrogen adsorption–desorption isotherm measurement suggest that the pillared derivatives are nanoporous materials with the highest BET specific surface area of ca. 116 m2/g. 相似文献
8.
Thermodynamic properties of a solid solution, MgyU1−yO2+x, at low magnesium concentrations have been investigated using the solid galvanic cell technique. The emf values were found to vary linearly with temperature in the range 850 1050 °C, from which the linear temperature dependence of partial molar free energy of oxygen,
, and the temperature independence of
and
were derived. These thermodynamic quantities were obtained as a function of x and y. Agreement of these values with those from theoretical considerations was examined. The effect of magnesium incorporation on
was expressed using
of UO2+x as
. 相似文献
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9.
The compositions in the YBa2−xLaxCu3O7−δ (0x0.2) system were prepared by the solid state reaction, employing a novel high-temperature oxygen sintering route. The modified sintering route yields dense slab like microstructures with large grains. The decomposition (incongruent melting) temperature of the YBa2Cu3O7−δ (Y-123) phase was found to shift to higher temperatures with increasing oxygen partial pressure and lanthanum content. Structure remained orthorhombic up to x=0.2 with a decrease in the orthorhombic strain ((b−a)/b). Iodometric titration indicated a systematic increase in the oxygen content with increasing lanthanum content. Thermo-gravimetric studies in various oxygen partial pressures revealed that the oxygen diffusion in to the YBa2Cu3O7−δ (δ>0.5) lattice is an exothermic event and takes place at temperatures not less than 573 K. High-temperature thermal-expansion measurements in air indicated that the nonlinearity in thermal expansion behaviour was reduced by the substitution of lanthanum. 相似文献
10.
In the context, SrxY10−x(SiO4)y(PO4)6−yO2 doped with 1 mol%Eu3+ (x = 2, y = 6; x = 4, y = 4; x = 5, y = 3; x = 8, y = 0) were synthesized by using 3-aminopropyl-triethoxysilane (APES) as the sources of the silicate network. X-ray diagrams confirm that SrxY10−x(SiO4)
y(PO4)6−yO2: Eu3+ solid solutions are formed as a pure apatitic phase. The SEM picture shows that there exist some novel unexpected coral like morphological structures. The luminescent intensity is the strongest for the host composition of Sr4Y6(SiO4)4(PO4)2O2 although the effect of the composition on the luminescent intensity is little. 相似文献
11.
Richard Harrington Gabrielle C. Miles Anthony R. West 《Journal of solid state chemistry》2008,181(2):334-339
Zn7Sb2O12 forms a full range of Co-containing α solid solutions, Zn7−xCoxSb2O12, with an inverse-spinel structure at high temperature. At low temperatures for x<2, the solid solutions transform into the low temperature β-polymorph. For x=0, the β→α transition occurs at 1225±25 °C; the transition temperature decreases with increasing x. At high x and low temperatures, α solid solutions are formed but are non-stoichiometric; the (Zn+Co):Sb ratio is >7:2 and the compensation for the deficiency in Sb is attributed to the partial oxidation of Co2+ to Co3+. From Rietveld refinements using ND data, Co occupies both octahedral and tetrahedral sites at intermediate values of x, but an octahedral preference attributed to crystal field stabilisation, causes the lattice parameter plot to deviate negatively from the Vegard's law. Sub-solidus compatibility relations in the ternary system ZnO-Sb2O5-CoO have been determined at 1100 °C for the compositions containing ?50% Sb2O5. 相似文献
12.
Y. Brard C. Michel M. Hervieu N. Nguyen F. Studer A. Maignan B. Raveau F. Boure 《Journal of solid state chemistry》2003,170(2):424-434
The possibility to synthesize layered oxycarbonates, with nominal composition Sr4Fe2−xMnxO6CO3 involving trivalent manganese, with 0≤x≤1.5, is reported for the first time. The structural study of Sr4FeMnO6CO3 using NPD, HREM, Mössbauer and XANES, shows that this phase is closely related to n=3 member of the Ruddlesden–Popper family. It derives from the latter by replacing the middle layer of transition metal octahedra by triangular CO3 groups, with two different “flag” and “coat hanger” configurations. The magnetic order is antiferromagnetic and fundamentally different from the magnetic behavior of Sr4Fe2O6CO3. 相似文献
13.
The stoichiometry, polymorphysm, and electrical behaviour of solid solutions of La0.5+y+xLi0.5−3xTi1−3yMn3yO3with perovskite-type structure have been studied. Data are given in the form of a solid solution triangle, phase diagrams, XRD patterns for the three polymorphs, A,β, and C, composition-dependence of their lattice parameters, and ionic and electronic conductivity plots. Microstruture and composition were studied by SEM/EDS and electron probe microanalysis. These compounds are mixed conductors. Ionic conductivity decreases when the amount of lithium diminishes and electronic conductivity increases with manganese content. 相似文献
14.
Sodium insertion in the tetrahedral layer structure of the ferrites Ba2−xSrxFe4O8 was performed by solid state reaction at 1220 K in air. Superstoichiometric oxides with the actual formula (Ba2−xSrx)1−y/4NayFe4O8—y0.56; 0.60Ba/Sr1.67—were characterized by X-ray and neutron powder diffraction. The hexagonal unit-cell volume shows an increasing dependence on the sodium insertion when the Ba/Sr ratio reaches the largest values. The marked expansion of the c parameter is the likely signature of the location of the inserted sodium cations within the interlayer space. One-half of the sodium cations partly sits on the Sr(Ba) sites in octahedral coordination and the other half occupies extra octahedral and tetrahedral sites. ac conductivity measurements point to a cationic conductivity whose thermally activated regime—Ea 0.7 eV—evidenced from 570 K, is unsensitive to the sodium content. The bottleneck of the 2D sodium mobility regards the crossing of the oxygen triangular faces shared by the different polyhedra within the interlayer space. 相似文献
15.
Fernanda M. Da Costa Robert Greatrex Norman N. Greenwood 《Journal of solid state chemistry》1977,20(4):381-389
The magnetic, electronic, and structural properties of the solid solutions LaxSr1−xRuO3 and LaxCa1−xRuO3 have been studied by 99Ru Mössbauer spectroscopy and other techniques. The LaxCa1−xRuO3 phases are reported for the first time and have been shown by powder X-ray diffraction measurements to be orthorhombically distorted perovskites. Electrical resistivity measurements on compacted powders show that all the phases are metallic with p 10−3, ohm-cm. Progressive substitution of Sr2+ by La3+ in ferromagnetic SrRuO3 leads to a rapid collapse of the magnetic hyper-fine splitting at 4.2°K. For x = 0.25 some ruthenium ions still experience a magnetic field but for 0.4 x 0.75 only single, narrow resonance lines are observed, consistent both with the complete removal of the ferromagnetism and with the presence of an averaged ruthenium oxidation state in each phase, i.e., Lax3+Sr1−x2+Ru(4−x)+O3 rather than Lax3+Sr1−x2+Rux3+Ru1−x4+O3. LaRuO3 and CaRuO3 both give essentially single-line spectra at 4.2°K, indicating that the ruthenium ions in these oxides are not involved in long-range antiferromagnetic order but are paramagnetic. The solid solutions LaxCa1−xRuO3 (0 < x 0.6) give sharp symmetrical singlets with chemical isomer shifts (relative to the Ru metal) which move progressively from the value characteristic of Ru4+ (−0.303 mm sec−1) toward the value for Ru3+ (−0.557 mm sec−1), consistent with the presence of intermediate ruthenium oxidation states in these phases also. 相似文献
16.
Dy5Ni0.66Bi2.34 and Lu5Ni0.56Sb2.44 were synthesized by arc-melting and were found to adopt an orthorhombic Yb5Sb3-type structure. Cell parameters are a = 12.075(2), b = 9.165(2), c = 8.072(1) Å for Dy5Ni0.66Bi2.34 and a = 11.6187(9), b = 8.933(1) and c = 7.8377(6) Å for Lu5Ni0.56Sb2.44. Dy5Ni0.66Bi2.34 undergoes a step-like ferromagnetic transition around 66 K. Magnetocaloric effect in terms of the magnetic entropy change, ΔS, reaches −3.73 J/kg K at 75 K for Dy5Ni0.66Bi2.34. 相似文献
17.
Compounds of the general formula V2 − yWyO5 + δ < eqid3 > nH2O (0 < y ≤ 0.25) with the layered structure of polyvanadic acid V2O5 < eqid4 > nH2O (H2V12O31 − δ < eqid5 > nH2O) have been prepared from peroxide solutions using the sol–gel process. The samples contain up to 5–8 wt% vanadium (IV). The water content changes within the range of 0.7 ≤ n ≤ 1.5 in depending on tungsten concentration. The V2 − yWyO5 + δ < eqid6 > nH2O (y ≤ 0.125) form the thin films described an interlayer distance of 11.60 ± 0.05 Å. The thermal properties, IR, and X-ray photoelectron spectra of the compounds synthesized have been studied. The thermal stability of the phases increases with the rising of tungsten content. The dehydration finishes with the forming solid solution V2−yWyO5 and WO3. The electrical conductivity of V2−yWyO5 + δ < eqid7 > nH2O (0 < y ≤ 0.25) powders was measured between 293 and 473 K at a relative humidity of 12%. The activation energy of conduction is independent upon the W content and equals 0.22–0.24 eV. Partial substitution of vanadium for tungsten was found to reduce the conductivity of the phases. The conductivity of the films increases with the increasing of relative air humidity and is governed by proton diffusion across the V-O-W layers. 相似文献
18.
Sylvie Malo Antoine Maignan Sylvain Marinel Maryvonne Hervieu Kenneth R. Poeppelmeier Bernard Raveau 《Solid State Sciences》2005,7(12):1492
Recently, the ferroelectromagnet YMnO3 has been the focus of interest because it exhibits both antiferromagnetism (Néel temperature 80 K) and ferroelectricity (Curie temperature 914 K). There have been no reports of complete YMn1−xMxO3 solid solutions in which substitution of the foreign M cation preserves the hexagonal P63cm structure. In contrast there exist several homeotypic phases with the general formula, Ln1+nCunMO3+3n (n=1 (M=Ti), 2 (M=V) and 3 (M=Mo); Ln: lanthanide). Several YMn1−x(Cu3/4Mo1/4)xO3 compounds have been synthesized. The solid solution, from YMnO3 (x=0) to YCu3/4Mo1/4O3 (x=1) has been characterized by X-ray diffraction and transmission electron microscopy study. For 0<x<0.9, the compounds are found to crystallize in the non-centrosymmetric structure, space group P63cm, of YMnO3. The Mn-free end member, x=1, crystallizes in a complex multiple cell, the superstructure being associated to Cu3+/Mo6+ cationic ordering. Dilution of the Mn3+ magnetic array by the paramagnetic (Cu2+) and diamagnetic (Mo6+) cations is found to decrease the antiferromagnetic ordering temperature and it becomes undetectable for x0.5 compositions. 相似文献
19.
Franois Roulland Michaël Josse Elias Castel Mario Maglione 《Solid State Sciences》2009,11(9):1709-1716
The present work reports the optimisation of the composition and elaboration process of Ba6−2xLn2xFe1+xNb9−xO30 (0.6 < x < 1.0), a composite multiferroic below 440 K. Both firing and sintering conditions have been investigated in order to lower the two spurious phases content and to improve the ceramic quality. The Eu content has also been varied, with subsequent adjustment of cationic content to maintain charge compensation and site occupancies. The evolution of phase content, dielectric and magnetic properties has been evaluated with respect to these parameters. It was found that optimal processing parameters allow a significant improvement of dielectric properties but leave magnetic properties unaffected. Eu content modification impacts both the dielectric and magnetic properties of the TTB samples and changes their dielectric behaviour from ferroelectric to relaxor. 相似文献
20.
Shijing Zhan Xuefeng Zhu Baofeng Ji Weiping Wang Xiaoliang Zhang Jibo Wang Weishen Yang Liwu Lin 《Journal of membrane science》2009,340(1-2):241-248
Asymmetrical thin membranes of SrCe0.95Y0.05O3−δ (SCY) were prepared by a conventional and cost-effective dry pressing method. The substrate consisted of SCY, NiO and soluble starch (SS), and the top layer was the SCY. NiO was used as a pore former and soluble starch was used to control the shrinkage of the substrate to match that of the top layer. Crack-free asymmetrical thin membranes with thicknesses of about 50 μm and grain sizes of 5–10 μm were successfully pressed on to the substrates. Hydrogen permeation fluxes (JH2) of these thin membranes were measured under different operating conditions. At 950 °C, JH2 of the 50 μm SCY asymmetrical membrane towards a mixture of 80% H2/He was as high as 7.6 × 10−8 mol/cm2 s, which was about 7 times higher than that of the symmetrical membranes with a thickness of about 620 μm. The hydrogen permeation properties of SCY asymmetrical membranes were investigated and activation energies for hydrogen permeation fluxes were calculated. The slope of the relationship between the hydrogen permeation fluxes and the thickness of the membranes was −0.72, indicating that permeation in SCY asymmetric membranes was controlled by both bulk diffusion and surface reaction in the range investigated. 相似文献