Synthesis and characterization of the La1−xSrxFeO3−δ system and the fluorinated phases La1−xSrxFeO3−xFx

The oxyfluorides La_1−xSr_xFeO_3−xF_x have been prepared by fluorination of the precursor oxides La_1−xSr_xFeO_3−δ via a low temperature route using poly(vinylidene fluoride) (PVDF). The structures of the oxides and oxyfluorides were investigated in detail by the Rietveld analysis of powder diffraction data. The oxyfluorides crystallize in the space group Pnma for 0<x≤0.9 (SrFeO₂F itself is cubic, space group Pm-3m) and show a sort of two-step structural distortion for decreasing x. Furthermore, a structural comparison of the oxyfluorides with the oxides is given, revealing an increase of the volume per La_1−xSr_xFeX₃ unit during fluorination, of which the magnitude highly depends on the value of x.     

Preparation of a single-phase solid electrolyte La1 ? xSrxGa1 ? yMgyO3 ? (x + y)/2 by self-propagating high-temperature synthesis

Highly dispersed single-phase powders described as La_0.88Sr_0.12Ga_0.82Mg_0.18O_2.85 were prepared using a method based on the principles of self-propagating high-temperature synthesis (SHS). Lanthanum, strontium, gallium, and magnesium nitrates were used in the SHS as “oxidants”, and ethylene glycol was used as the reducing agent. The initial reaction mixture was liquid. According to X-ray diffraction and scanning electron microscopy data, the sample becomes a single phase after annealing of the primary SHS product at 1200°C, which is substantially lower than in other synthetic methods. Using so active powders (grain size of about 100–130 nm), it is possible to reduce the temperature of the final annealing of the ceramics to 1275°C, which gives rise to single-phase finely dispersed ceramics having specific properties.     

层状钙钛矿型Sm2-2xSr1+2x-2yCa2yMn2O7(x=0.2，0.3，0.4，0.5；y=0，0.2，0.3)的溶胶凝胶合成及电性能研究

Layered perovskite manganites with a nominal chemsitry of Sm_2-2xSr_1+2x-2_yCa_2yMn₂O₇(x=0.2, 0.3, 0.4, 0.5; y=0, 0.2, 0.3) were prepared using sol-gel method. The crystal structures of these compounds were studied by X-ray diffraction (XRD) and FTIR absorption spectra. The absorption peaks become weaker and move a little to higher frequency with increasing of Sm/Sr concentration. As the Sm doping increases to x=0.2 and x=0.3, the absorption peaks show a cubic structure character, reflecting that the samples suffer from a transition from tetragonal structure to cubic structure. This coincides with the X-ray diffraction results. The high temperature electrical properties were studied by conventional four-probe method. Although all samples exhibit the semiconductive behavior, lnρ-1 000/T curves are not linear and they obey the small polaron hopping mechanism. Moreover, the resistivity decreases with x reducing. This is due to that Sm doping increases the Jahn-Teller ion Mn³⁺/Mn⁴⁺ ratio, and decreases the e_g bandwidth.     

Phase diagram, chemical stability and physical properties of the solid-solution Ba4Nb2−xTaxO9

Through the construction of the Ba₄Nb_2−xTa_xO₉ phase diagram, it was discovered that the unique high-temperature γ phase is a thermodynamic intermediate between the low-temperature α phase (Sr₄Ru₂O₉-type) and a 6H-perovskite. Refined site occupancies for the γ phase across the Ba₄Nb_2−xTa_xO₉ solid-solution indicate that Nb preferentially occupies the tetrahedral sites over the octahedral sites in the structure. When annealed in a CO₂-rich atmosphere, all of the phases studied absorb large amounts of CO₂ at high temperatures between ∼700 and 1300 K. In situ controlled-atmosphere diffraction studies show that this behaviour is linked to the formation of BaCO₃ on the surface of the material, accompanied by a Ba₅(Nb,Ta)₄O₁₅ impurity phase. In situ diffraction in humid atmospheres also confirms that these materials hydrate below , and that this plays a critical role in the various reconstructive phase transitions as well as giving rise to proton conduction.     

Synthesis, Crystal Structure, and Magnetic Properties of Quasi-One-Dimensional Oxides Ca3CuMnO6 and Ca3Co1+xMn1−xO6

Synthesis conditions, crystal structures, and magnetic properties of quasi-one-dimensional complex oxides Ca₃CuMnO₆ (space group P-1, z=4, triclinic cell) and Ca₃Co_1+xMn_1−xO₆ with x=0, 0.25, 1.0 (structural type K₄CdCl₆, space group R-3c, z=6) are presented. The crystal structures of Ca₃CoMnO₆ and Ca₃CuMnO₆ were refined using neutron and combined X-ray and neutron diffraction analysis, respectively. The interatomic distances in oxygen polyhedra were found. In contrast to ferromagnetic Ca₃Co₂O₆ (T_c=24 K), manganese-containing phases Ca₃Co_1+xMn_1−xO₆ are characterized by antiferromagnetic interactions with Neel temperatures 18 K (x=0.25) and 13 K (x=0). For Ca₃CuMnO₆T_N was established to be 6 K.     

Regions of stability of variable-composition perovskite phases La1?xSrxMn1?yMyO3 (M = Ti, Ni)

The formation of the orthorhombic solid solution series LaMn_1−y Ti _y O₃ with 0.0 ≤ y ≤ 0.15 and LaMn_1−y Ni _y O₃ with 0.0 ≤ y ≤ 0.4 was observed. The stability boundaries of the La_1−x Sr _x Mn_1−y M _y O₃ (M = Ti, Ni) perovskite phases were determined. Fragments of isobaric-isothermal sections of the phase diagrams of the La₂O₃-SrO-Mn₃O₄-TiO₂ and La₂O₃-SrO-Mn₃O₄-NiO systems in air at 1100°C were suggested. Original Russian Text ? E.A. Filonova, A.N. Demina, A.N. Petrov, 2007, published in Zhurnal Fizicheskoi Khimii, 2007, Vol. 81, No. 10, pp. 1787–1790.     

Thermodynamic Quantities and Defect Structure of La0.6Sr0.4Co1−yFeyO3−δ(y=0–0.6) from High-Temperature Coulometric Titration Experiments

The partial energies and entropies of O₂in perovskite-type oxides La_0.6Sr_0.4Co_1−yFe_yO_3−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.     

Phase composition, electroconductivity, oxygen ion transport number, and microhardness of Ln1 ? xSrxGa0.5 ? y/2Al0.5 ? y/2MgyO3 ? δ (Ln = La, Pr, Nd; x, y = 0.10, 0.15)

Phase composition, electroconductivity, oxygen ion transport number, and microhardness of samples of Ln_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} (Ln = La, Pr, Nd; x, y = 0.10, 0.15) synthesized by a ceramic methods are studied. Methods of x-ray diffraction analysis and scanning electron microscopy reveal the La-containing samples to be homogeneous and have a perovskite structure. Magnesium does not dissolve in Pr-and Nd-containing systems but forms an individual phase based on magnesium oxide. Apart from magnesium oxide, in these systems there form extrinsic phases, specifically, LnSrGa₃O₇ and an unknown phase. The electroconductivity of La_{1 − x} Sr_xGa_{1 − y} Mg_yO_{3 − δ} decreases after substituting Al for Ga. Ceramic La_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_3−δ is a purely ionic conductor in the temperature interval 500 to 1000°C; Nd_xSr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} has predominantly ionic conduction; and the predominant type of conduction in Pr_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} is electronic below 700–800°C, with the contribution of ionic conduction increasing at higher temperatures. Substituting Al for Ga raises the hardness of ceramics under study. Among the compositions studied, La_0.85Sr_0.15Ga_0.45Al_0.45Mg_0.10O_{3 − δ} and La_0.85Sr_0.15Ga_0.425Al_0.425Mg_0.15O_{3 − δ} exhibit a combination of electroconductivity and hardness that is optimal for application as electrolyte at reduced temperatures (600–800°C). The Pr_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} system possesses mixed ionic-electronic conduction and high hardness, which makes it appealing for application as oxygen-penetrable membranes. Original Russian Text ? Yu.V. Danilov, A.D. Neuimin, L.A. Dunyushkina, L.A. Kuz’mina, N.S. Zybko, Z.S. Martem’yanova, A.A. Pankratov, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 1, pp. 57–65.     

A Structural Investigation of Ga3−xIn5+xSn2O16

The structure of the recently reported transparent conductor, Ga_3−xIn_5+xSn₂O₁₆(0.3<x<1.6), was established by a combination of high-resolution electron microscopy, convergent-beam electron diffraction, and Rietveld analysis of powder diffraction data (X-ray and time-of-flight neutron methods). This “T-phase” compound has an anion-deficient fluorite-derivative structure whose space group isI4₁/a. Although there are similarities to the parent oxide structures, the T-phase lacks one of the distorted InO₆octahedra observed in In₂O₃, which may account for its inability to be donor-doped by Sn.     

Magnetic Study of OrthomanganitesA1−xMnO3+y(A=La, Eu) with the Perovskite Structure

The crystal structure and magnetic properties of orthomanganitesA_1−xMnO_3+y(A=La, Eu;x≤0.2;y≤0.13) were investigated. It was shown that the increase of oxygen content leads to the transformation from the weak ferromagnetic to the ferromagnetic state in these compounds. The Curie temperatures of La_1−xMnO_3+yand freezing temperatures of magnetic clusters for Eu_1−xMnO_3+yin the samples with a deficit ofAcations are higher than those in parent compounds (withx=0). A mixed magnetic state involving ferro- and antiferromagnetic domains is suggested in the intermediate range ofx,yvalues. Arguments are presented to support the assumption that the magnetic properties in the lightly doped insulating regime are governed by superexchange via anions rather than by exchange via charge carriers.     

Pressure Dependence of the Lattice Distortion in Perovskite La0.5−xBixCa0.5MnO3 (x=0.1, 0.15, 0.2)

The in situ behavior of distorted perovskite La_0.5−xBi_xCa_0.5MnO₃ (x=0.1, 0.15, 0.2) under high pressure has been studied by energy-dispersive X-ray diffraction in a diamond anvil cell. An abnormal change of the 202–040 d-spacing ascribed to the disappearance of the distortion mode Q₂ in the MnO₆ octahedra is observed at 1.2, 1.4, and 1.6 GPa, respectively, and it results in a reduction of the Jahn–Teller distortion commonly existing in the manganites. Effect of the unique 6s² long-pair character of the Bi³⁺ ion on the pressure dependence of the lattice distortion is discussed.     

The oxycarbonates Sr4(Fe2−xMnx)1+y(CO3)1−3yO6(1+y): nano, micro and average structural approach

The possibility to synthesize layered oxycarbonates, with nominal composition Sr₄Fe_2−xMn_xO₆CO₃ 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.     

Synthesis, structure and oxygen nonstoichiometry of La0.4Sr0.6Co1−yFeyO3−δ

The samples of La_0.4Sr_0.6Co_1−yFe_yO_3−δ (y = 0.2 and 0.4) were prepared using both conventional ceramic technique and nitrate–citrate precursors technique. The phase identification was made by X-ray diffraction method. The refinement of structural parameters from the XRD and neutron diffraction measurements was performed by full profile Rietveld analysis. Neutron diffraction showed that both samples possess distorted perovskite-type structure. Oxygen nonstoichiometry was measured by chemical analysis and thermogravimetry (TG) analysis in the range 20 ≤ T/°C ≤ 900 and 2E-5 ≤ pO₂/atm ≤ 4E-1. TG-experiments indicate a relatively fast and reversible oxygen exchange at pO₂ > 1E-2 atm. Mass saturation occurs at T < 300 °C upon cooling. The absolute value of oxygen nonstoichiometry was determined by iodometric titration measurements. It was found that both samples have practically stoichiometric composition at 300 °C in air and δ increases with increasing temperature and decreasing oxygen partial pressure.     

Crystal chemistry, modulated structure, and electrical conductivity in the oxygen excess scheelite-based compounds La1−xThxNbO4+x/2 and LaNb1−xWxO4+x/2

For La_1−xTh_xNbO_4+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 LaNb_1−xW_xO_4+x/2 for 0.11 ≤ x ≤ 0.22. Additional phases occur at La_0.2Th_0.8NbO_4.4 and LaNb_0.4W_0.6O_4.3. The electrical conductivity and the direction and wavelength of the structural modulation have been characterized for the La_1−xTh_xNbO_4+x/2 phase with 0.075 ≤ x ≤ 0.37.     

Study of dielectric properties of single phase Bi1−xCaxFeO3 (x = 0.1, 0.3, 0.5)

A series of Bi_1−xCa_xFeO₃ (x = 0.1, 0.3, 0.5) multiferroic samples have been prepared in order to study the effect of different concentrations of Ca on the crystal structure, and dielectric properties. Structural analysis has been performed using X-ray diffraction (XRD) measurements. Rietveld refined XRD data confirm that all the samples are of single phase, having hexagonal structure with R3c space group. Cell parameters decrease systematically with increase in Ca concentration. Dielectric measurements have been performed in the temperature range of 200–450 K at selected frequencies in the range 100–1100 kHz. A near room temperature ferroelectric anomaly has been observed in all the samples which shift toward lower temperature with increase in doping. Conduction activation energies are calculated and found to decrease with increasing doping.     

Pillaring of Layered Perovskites, K1−xLaxCa2−xNb3O10, with Nanosized Fe2O3 Particles

Nanosized Fe₂O₃ clusters are pillared in the interlayer spaces of layered perovskites, H_1−xLa_xCa_2−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 (E_g2.25 eV) is slightly larger than that of bulk Fe₂O₃ (E_g2.20 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.     

Pyrochlore phases in the system ZnOBi2O3Sb2O5: II. Crystal structures of Zn2Bi3.08Sb2.92O14+δ and Zn2+xBi2.96−(x−y)Sb3.04−yO14.04+δ

Rietveld refinement of combined X-ray and neutron diffraction data has, within errors, confirmed the stoichiometries of two, cubic pyrochlore phases in the ZnOBi₂O₃Sb₂O₅ system. Neither phase has the ‘ideal’ stoichiometry, Zn₂Bi₃Sb₃O₁₄. One phase, P₁, is a Zn-rich, Bi-deficient solid solution Zn_2+xBi_{2.96−(x−y)}Sb_3.04−yO_14.04+δ. The other, P₂, is a Bi-rich line phase, stoichiometry Zn₂Bi_3.08Sb_2.92O_14+δ. Both structures have a mixture of Bi, Zn on the A-sites and Zn, Sb on the B-sites. However, Zn is displaced off-centre in the A-sites to achieve lower co-ordination number with realistic ZnO bond lengths. Additional structural complexities arise from: displacement of O(2) atoms; partial occupancies of O(1) and O(2) sites; partial occupancy of a third, interstitial oxygen site, O(3). Since the multiplicities of the off-centre sites are much higher than those of the ideal positions, there is considerable possibility for correlated short range order throughout the structures.     

Oxygen deficiency and phase transitions in SrCo1– x – y Fe x Cr y O3–δ ( x =0.10–0.40, y =0–0.05)

Oxygen-deficient phases based on perovskite-like strontium cobaltites-ferrites are promising mixed conductors for high-temperature electrochemical applications. The p(O₂)-T-δ diagrams for the oxide systems SrCo_{1– x – y} Fe _x Cr _y O_{3– δ} (x=0.10–0.40; y=0–0.05) were studied at 500–1000 °C in the oxygen pressure range from 10^–5 to 0.21 atm using the coulometric titration technique and thermogravimetric analysis. Stability limits of the cubic perovskite phases having a high oxygen ionic conductivity were evaluated as functions of temperature, oxygen partial pressure and oxygen nonstoichiometry. It was found that doping with chromium and increasing the iron content in SrCo(Fe,Cr)O_{3– δ} both lead to a considerable enlargement of the cubic perovskite phase existence domain towards lower temperatures and reduced oxygen pressures. Electronic Publication     

Diffraction and DAFS Studies of a Ba4(BaxPt1−x)Pt2O9Twinned Crystal, a Member of the Bap(BaxPt1−x)Ptp−2O3p−3Series

Crystallographic studies of the Ba–Pt–O system have been undertaken using X-ray and electron diffraction techniques. The system is described by means of a Ba_p(Ba_xPt²⁺_1−x)Pt⁴⁺_p−2O_3p−3formula which corresponds to a BaO₃hexagonal based framework with Pt chains, whereprepresents the oxygen deficiency and the presence of both Pt⁴⁺and Pt²⁺cations in the compounds, andxa possible substitution of Pt²⁺by Ba²⁺in trigonal prismatic sites. The structure of a Ba₄(Ba_0.04Pt²⁺_0.96)Pt⁴⁺₂O₉crystal has been solved by using 5548 X-ray difraction reflections collected on a twinned crystal. Refinements were performed with two distinct models: an “average”P321 space group and an “orthorhombic”C2 space group with cell parametersa=17.460(4) Å,b=10.085(2) Å,c=8.614(3) Å. In this structure, two Pt⁴⁺and one Pt²⁺cations are distributed over four Ba planes and form chains along thecaxis, consisting of two face-sharing Pt⁴⁺O₆octahedra connected with one Pt²⁺O₆trigonal prism. A lattice misfit occurs between the rigid barium lattice and the PtO₃chains, giving rise to a composite structure. Twinning and domain configurations are described and taken into account in the refinement. This twinning is related to the presence of Pt²⁺cations, whose positions break the threefold axis symmetry. A diffraction anomalous fine structure (DAFS) study was also performed on this twinned single crystal. Anomalous scattering factorsf′ andf″ for platinum in this crystal were refined near the L_IIIPt absorption edge. They confirm the weak barium occupancy of the trigonal prismataic site and the Pt⁴⁺valence of the octahedral sites. Reflection overlaps, due to twinning, flatten the DAFS sensitivity to Pt atoms in the prismatic sites and did not allow their clear valence determination, but Pt–O bond lengths agree with the presence of Pt²⁺cations at the center of prismatic faces. Electron diffraction patterns of powders having slightly different composition show a continuous evolution of incommensurate Bragg peaks and a weak correlation between the PtO₃chains. They also confirm the composite nature and the one-dimensionality of the Ba_p(Ba_xPt²⁺_1−x)Pt⁴⁺_p−2O_3p−3series, which can produce highly anisotropic physical properties.     

正极材料Li(Ni0.5Mn0.5)1-xMxO2 (M=Ti，Al；x=0，0.02)电化学行为的比较研究

0IntroductionMany efforts have been made to develop newmaterials as an alternative to LiCoO2due to the rela-tively high cost and toxicity of Co.Much attention hasbeen paid to layered structure cathode materials suchas LiMnO2and LiNiO2due to their lower co…