The Crystal Structures, Microstructure and Ionic Conductivity of Ba2In2O5 and Ba(InxZr1−x)O3−x/2

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(In_xZr_1−x)O_3−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(In_xZr_1−x)O_3−x/2 samples with x=0.1 to 0.9 adopt the cubic perovskite structure, with the lattice parameter increasing with x.     

Specific heat on Sr<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>7</Subscript> and Sr<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>7</Subscript>

Summary Specific heats on the single crystals of Sr₂Nb₂O₇, Sr₂Ta₂O₇ and (Sr_1-xBa_x)₂Nb₂O₇ were measured in a wide temperature range of 2-600 K. Heat anomalies of a λ-type were observed at the incommensurate phase transition of T_INC (=495 K) on Sr₂Nb₂O₇ and at the super-lattice phase transition of T_SL (=443 K) on Sr₂Ta₂O₇; the transition enthalpies and the transition entropies were estimated. Furthermore, a small heat anomaly was observed at the low temperature ferroelectric phase transition of T_LOW (=95 K) on Sr₂Nb₂O₇. The transition temperature T_LOW decreases with increasing Ba content x and it vanishes for samples of x>2%.     

A TEM, XRD, and crystal chemical investigation of oxygen/vacancy ordering in (Ba1−xLax)2In2O5+x, 0x0.6

A careful TEM and XRD study of the (Ba_1−xLa_x)₂In₂O_5+x, 0x0.6, ‘defect-perovskite’-type solid solution has been carried out. A well-defined structural phase transition is shown to occur between x=0.1 and 0.2 from the orthorhombic brownmillerite structure type on the low x side to a multiple twinned, tetragonal 1×1×2 perovskite-related superstructure phase on the high x side at x=0.2. This phase transition correlates with an important phase transition previously observed in electrical conductivity versus temperature measurements. The existence of additional satellite reflections close to the regions of reciprocal space was found to be typical of all (Ba_1−xLa_x)₂In₂O_5+x specimens, although their intensity relative to the parent Bragg reflections systematically reduces as x increases. As x increases beyond 0.2, the -type satellite reflections initially become weaker and rather more diffuse for x=0.3 before splitting into pairs of rather weak and somewhat diffuse incommensurate satellite reflections for x=0.4 and beyond. An interpretation in terms of oxygen vacancy ordering and associated structural relaxation is given. Additional structured diffuse scattering is also observed and a tentative explanation in terms of Ba/La ordering and associated local strain distortions put forward.     

Hydration and forms of oxygen-hydrogen groups in Oxyfluorides Ba2 ? 0.5x In2O5 ? x F x

A number of fluorine-substituted compounds were synthesized from brownmillerite Ba₂In₂O₅. The homogeneity range of the Ba_{2 ? 0.5x} In₂O_{5 ? x} F _x solid solution (x ?? 0.3) was determined by X-ray diffractometry. The studied phases were found to be able to incorporate water from the gas phase, due to which their orthorhombic structure transforms into tetragonal one. The degree of hydration decreased as the fluorine content in the solid solution increased. As in the case of Ba₂In₂O₅, the energetically nonequivalent hydroxo groups were found to be the main form of oxygen-hydrogen groups.     

Zur Kristallstruktur von Ba3In2O6

About the Crystal Structure of Ba₃In₂O₆ Single crystals of Ba₃In₂O₆ could be prepared by recrystallization of a flux and by solid state reaction in closed platinium tubes, respectively. Ba₃In₂O₆ crystallizes with tetragonal symmetry (space group 14/mmm, a = 4.1868; c = 21.7041 Å, Z = 2). Single crystal X-ray work lead to a crystal structure like La_2-xSr_1+xCu₂O_6-δ therefor Ba₃In₂O₆ is a modified member of the Sr₃Ti₂O₇-Type. The coordinations of Ba²⁺ and In³⁺ are described and the relations to the Sr₃Ti₂O₇-type are discussed.     

Composition-induced structural phase transitions in the (Ba1−xLax)2In2O5+x (0?x?0.6) system

Composition-induced structural phase changes across the high temperature, fast oxide ion conducting (Ba_1−xLa_x)₂In₂O_5+x, 0?x?0.6, system have been carefully analysed using hard mode infrared (IR) powder absorption spectroscopy, X-ray powder diffraction and electron diffraction. An orthorhombic brownmillerite to three-dimensionally disordered cubic perovskite phase transition in this system is signalled by a drastic change in slope of both wavenumber and average line widths of IR spectra as a function of composition. Some evidence is found for the existence of an intermediate tetragonal phase (previously reported to exist from electron diffraction data) around x∼0.2. The new spectroscopic data have been used to compare microscopic and macroscopic strain parameters arising from variation in composition. The strain and spectroscopic data are consistent with first-order character for the tetragonal→orthorhombic transition, while the cubic→tetragonal transition could be continuous. Differences between the variation with composition of spectral parameters and of macroscopic strain parameters are consistent with a substantial order/disorder component for the transitions. There is also evidence for precursor effects within the cubic structure before symmetry is broken.     

Successive self-nucleation and annealing in the solvated state of ethylene copolymers

Summary Simultaneous TG/DSC and high temperature X-ray diffraction studies were performed on the system SrCO₃-Fe₂O₃ in an atmosphere of CO₂ from room temperature to 1300°C. SrCO₃ decomposes and reacts simultaneously with the Fe₂O₃ beginning around 850°C. A transient iron rich phase is formed initially, which soon diminishes to yield a mixture of perovskite SrFeO_3-x and the iron rich phase Sr₄Fe₆O₁₃. Upon cooling the perovskite phase predominantly orders into the brownmillerite structure Sr₂Fe₂O₅. There does not appear to be a Hedvall effect associated with the first order phase transformation in SrCO₃ at 927°C.     

Solid solutions of Ba2(In1 ? xAlx)2O5: Structural evolution and hydration processes

Solid solutions of the composition Ba₂(In_{1 − x} Al _x )₂O₅[VO]₁ (0 ≤ x ≤ 0.20) with an incomplete oxygen sublattice were obtained. It was established that, along with an increase in parameter x, there is disordering of oxygen vacant positions and a transition from the structure of brownmillerite to that of defect perovskite. It was demonstrated that the phases under study are characterized by an ability for reversible interaction with water vapors in the temperature range 150–450°C. During this process, proton defects, predominantly in the form of OH⁻ groups, are formed in the oxide structure. We conclude that in a number of solid solutions, the amount of intercalated water declines upon an increase in the aluminum content.     

Le système Ba2Fe2O5BaZnO2. I. Mise en évidence de trois nouvelles phases

In order to obtain phases with a high deficiency of oxygen, iron is progressively substituted by zinc in Ba₂Fe₂O₅ at 900–1000°C. For 0.05 < x < 0.40 ($\text{x =}\text{Zn}\text{Fe}\text{+}\text{Zn}$), the long-range order between tetrahedra and octahedra of the brownmillerite is destroyed and the cell is perovskite type with up to 23% oxygen vacancies. For x = 0.5 there is a new superlattice and an orthorhombic compound Ba₄Fe₂Zn₂O₉. For 0.7 < x < 0.9 a new cubic phase is formed which is related to BaZnO₂.     

Phase transition of negative thermal expansion Zr1-xHfxW2O8 solid solutions

A powder X-ray diffraction experiment was performed on cubic Zr_1-xHf_xW₂O₈ (x=0.25, 0.50 and 0.75) solid solutions from 90 to 560 K. The lattice parameters of Zr_1-xHf_xW₂O₈ at 121 K decreased linearly with increasing Hf contents, due to smaller ionic radius of hafnium than that of zirconium. Transition temperatures due to α-β structural phase transition increased with increasing Hf contents, reflecting the decrease of lattice free volume related to the orientation of unshared vertex of WO₄. Anomaly in the heat capacity of Zr_0.5Hf_0.5W₂O₈ was observed around 450 K which was 9 K lower than that by X-ray diffraction method. Transition entropy of Zr_0.5Hf_0.5W₂O₈ was 2.1 J mol^-1 K^-1, consistent with those of ZrW₂O₈ and HfW₂O₈. This consistent entropy supports that Zr_1-xHf_xW₂O₈ (x=0-1.0) has the same order-disorder phase transition mechanism. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and structural studies of Sr2Co2−xAlxO5, 0.3⩽x⩽0.5

Sr₂Co_2−xAl_xO₅, 0.3⩽x⩽0.5, with a perovskite related structure has been synthesized. The XRD powder patterns showed reflections from the basic cubic perovskite structure along with some additional weak superstructure reflections. Electron diffraction (ED) and high-resolution transmission electron microscopy (HRTEM) studies show that crystallites of Sr₂Co_2−xAl_xO₅ consist of small intergrown differently oriented domains, about 40 Å in diameter, with brownmillerite structure.     

原位制备钛酸锶钡/铌酸锶钡复相陶瓷的研究

0引言驰豫型铁电陶瓷是近年来广泛研究和迅速发展的一种新型功能陶瓷[1]。通过把具有不同相变温度的驰豫型铁电体层层叠加,可以获得具有稳定的介电常数鄄温度关系的复合材料[2]。钛酸锶钡Ba1-xSrxTiO3和铌酸锶钡SrxBa1-xNb2O6都是重要的驰豫型铁电体,并且其居里温度均随Ba/Sr比     

Oxide-ion conductivity of the oxygen deficient perovskite solid-solution system, (Ba0.5-xSrxLa0.5)2(In1-yMy)2O5.5 (M=Y or Ga)

In order to elucidate the mechanism of oxide-ion conductivity for (Ba_0.5-xSr_xLa_0.5)(In_1-yM_y)₂O_5.5 (M=Y or Ga, 0<x<0.2, 0<y<0.2) solid-solution system, the electrical conductivity was measured as a function of oxygen partial pressure and temperature, and the results were investigated in terms of a dopant content and unit cell free volume. The system was confirmed to be an oxide-ion conductor from the oxygen partial pressure dependence on electrical conductivity. The oxide-ion conductivity increased with increasing the unit cell free volume at first. However, it showed a maximum at a value of free volume, and then decreased. The decreasing conductivity vs. the volume would be related to the crystal symmetry change. This revised version was published online in August 2006 with corrections to the Cover Date.     

Structure,Electrical and Oxygen Transport Properties of Fe-Doped SrCoO3?δ Perovskites

The structure-property relationship of Fe-doped SrCoO_3-δ was studied. With increase of Fe content in SrCo_1-xFe_xO_3-δ from x=0 to x=0.2, the phase composition changed progressively in the order of hexagonal→brownmillerite (main)+hexagonal→cubic (main)+brownmillerite→single cubic phase. Transition between the hexagonal/brownmillerite phase and the cubic phase took place with variation of the operating conditions, and was associated with remarkable changes in the electrical conductivity and oxygen permeation flux.     

Lattice-dynamics-based characterization of La1-xAxCoO3-δ (A = Sr,Ba) nanoparticles for an inert anode in molten salts

La_1-xA_xCoO_3-δ (A = Sr, Ba) nanoparticles used as an inert anode in molten salts were characterized using phonon vibrations, and their compositions and morphologies were investigated. These nanoparticles were used for nanostructure fabrication of an inert anode to reduce oxide ion transportation. The singularity structure changes with increasing Sr ion content in La_1-xSr_xCoO_3-δ nanoparticles showed a transient of spin state change from a low-spin state to intermediate- and/or high-spin states. The valencies of Co ion in La_1-xSr_xCoO_3-δ were 3.2 and 3.3 for La_0.8Sr_0.2CoO_3-δ and La_0.6Sr_0.4CoO_3-δ, respectively, suggesting that oxygen defects were introduced by Sr ion doping in La_1-xSr_xCoO_3-δ nanoparticles. In contrast, the valencies of Co ion in La_1-xBa_xCoO_3-δ were 3.1 and 3.0 for La_0.5Ba_0.5CoO_3-δ and La_0.4Ba_0.6CoO_3-δ, respectively, suggesting that oxygen defects were introduced slightly by Ba ion doping in La_1-xBa_xCoO_3-δ nanoparticles. The isotropic phonon vibrations of La_1-xA_xCoO_3-δ nanoparticles were estimated using high-temperature synchrotron radiation X-ray diffraction measurements. Crystal anisotropy measurements of phonon vibrations indicated that the oxide ions diffused preferentially along the (a, b) plane in the La_1-xSr_xCoO_3-δ crystal lattice and toward the c-axis direction in the La_1-xBa_xCoO_3-δ crystal lattice. These results suggest that the oxide ion transportation was curtailed using layered nanoparticles to fabricate an inert anode.

     

Phase Equilibria and Crystal Structure of Complex Oxides in the La–Sr–Co–Ni– System

Phase equilibria in the La–Sr–Co–Ni–O system were studied in air at 1100°. The samples for the study were synthesized by the standard ceramic and citrate processes. The limiting solubility and structure of La_1-xSr_xCo_1-yNi_yO_3- and (La_1-xSr_x)₂Co_1-yNi_yO₄ solid solutions were determined by Xray powder diffraction analysis. La_1-xSr_xCo_1-yNi_yO₃- solid solutions with 0 x 0.5 have a distorted rhombohedral perovskitelike structure (R c space group). An increase in the strontium concentration reduces the rhombohedral distortions, and the compounds with x < 0.5 have an ideal cubic structure (Pm3m space group). (La_1-xSr_x)₂Co_1-yNi_yO₄ crystals have a tetragonal K₂NiF₄ type unit cell (I4/mmm space group). The relationships between unit cell parameters and compositions were obtained for singlephase La_1-xSr_xCo_1-yNi_yO_3- and (La_1-xSr_x)₂Co_1-yNi_yO₄ samples. The existence regions of La_1-xSr_xCo_1-yNi_yO₃- and La_1-xSr_x)₂Co_1-yNi_yO₄ solid solutions were distinguished on P–T phase diagrams.     

Photocatalytic CO2 reduction by Cr-substituted Ba2(In2-xCrx)O5·(H2O)δ (0.04 ≤ x ≤ 0.60)

Cr-substituted polycrystalline Ba₂(In_2-xCr_x)O₅·(H₂O)_δ powders (0.04 ≤ x ≤ 0.60) were synthesized by solid state reaction to investigate the relation of crystal structure, thermochemical, magnetic, and optical properties. The Cr-substitution results in an unit cell expansion and formation of the higher-symmetric tetragonal phase together with increased oxygen and hydrogen contents. Magnetic property measurements reveal that the diamagnetic pristine Ba₂In₂O₅·(H₂O)_δ becomes magnetically ordered upon Cr-substitution. By UV–vis spectroscopy a gradual shift of the absorption-edge energy to lower values was observed. Numerical calculations showed that the observed bandgap narrowing was ascribed to the Cr induced states near the Fermi level. The correlation between the changes of crystal chemistry, magnetic, and optical properties of Cr-substituted Ba₂(In_2-xCr_x)O₅·(H₂O)_δ can be explained by the replacement of In by Cr. Consequently, an enhanced photocatalytic CO₂ reduction activity was observed with increasing Cr substitution, compatible with the state-of-the-art high surface area TiO₂ photocatalyst (P-25).     

Structural transitions at high temperature in Sr2Fe2O5

The high-temperature behavior of Sr₂Fe₂O₅ has been well characterized by various techniques (DTA, X-ray diffraction, magnetic measurements) paying particular attention to keep the nominal composition constant. The transition from the low-temperature ordered form (with brownmillerite structure) to the high-temperature disordered form (of perovskite structure) has been explained in terms of microdomain formation. A structural model is proposed and discussed.     

Synthesis,hydration, and electric properties of chlorine-substituted brownmillerite Ba<Subscript>1.95</Subscript>In<Subscript>2</Subscript>O<Subscript>4.9</Subscript>Cl<Subscript>0.1</Subscript>

Chlorine-substituted brownmillerite Ba_1.95In₂O_4.9C_l0.1 was obtained from barium indate Ba₂In₂O₅ by solid-phase synthesis. The ability to absorb water from the gas phase was confirmed by thermogravimetric studies. The transport properties were studied while varying the thermodynamic parameters of the external environment (T, pO₂, pH₂O). The chloride ions in the oxygen sublattice of barium indate Ba₂In₂O₅ were found to affect the ion conductivity. In a humid atmosphere, the sample exhibited proton conductivity (E _a = 0.54 eV), whose contribution became dominant below 300°C.     

Electric properties of oxyfluorides Ba2In2O5−0.5x F x with brownmillerite structure

Synthesis of fluoro-substituted substances based on brownmillerite Ba₂In₂O₅ is carried out. The width of the homogeneity region of the Ba₂In₂O_5?0.5x F _x (0 < x ≤ 0.25) solid solution was established using X-ray analysis. Measurement of temperature dependences of conductivity in atmospheres with different partial pressure of water vapor (pH₂O = 3.3 and 2 × 10³ Pa) showed an increase in conductivity at T ≤ 550°C in a humid atmosphere, which is due to appearance of proton transport. The dependence of conductivity on partial oxygen pressure (pO₂ = 0.21 × 10⁵ to 10^?15 Pa) is studied in the temperature range of 500–1000°C; ion transport numbers are calculated. The method of polarization measurements was used to determine transport numbers of fluoride. Total conductivity is divided into ion (proton, oxygen, and fluoride ion) and electron components. Analysis of concentration dependences of conductivities showed that low concentrations of fluoride allow increasing both the total and partial conductivities (oxygen-ion and proton) and, besides, allow shifting the “order-disorder” phase transition by 100°C to the low temperature range.