Site-sensitive X-ray photoelectron spectroscopy of Fe3O4 by photoelectron diffraction

Fe 2p core-level photoelectron spectra of magnetite were measured using soft X-ray and hard X-ray, and its emission angle dependence was investigated. The photoelectron diffraction pattern from different atomic sites differs because the atomic arrangement surrounding each site is different. By selecting the forward-focusing-peak (FFP) directions characteristic to each atomic site and measuring the kinetic energy dependence of the FFP intensities at the Fe 2p core-level range, we succeed in detecting the variation of the peak intensity of Fe 2p core-level spectra at different emission directions. This result, consistent with recent results, suggests that the lower-binding-energy peak of the Fe 2p core-level spectrum may be assigned as the B site component.     

Synthesis and X-ray diffraction study of Tm M 3 II Fe5O12 (MII = Ca, Sr, Ba) compounds

Double ferrites were synthesized by solid-phase annealing from thulium and iron oxides and alkaline-earth carbonates for the first time. Their symmetry systems and unit cell parameters were determined by X-ray diffraction analysis.     

Structural and spectroscopic properties of pure and doped Ba6Ti2Nb8O30 tungsten bronze

Pure and doped Ba(6)Ti(2)Nb(8)O(30) (BTN), obtained by substituting M = Cr, Mn, or Fe on the Ti site (Ba(6)Ti(2-x) M(x)Nb(8)O(30), x = 0.06 and 0.18) and Y and Fe on the Ba and Ti sites, respectively (Ba(6-x)Y(x)Ti(2-x)Fe(x)Nb(8)O(30), x= 0.18), are synthesized. The influence of cation doping on the local structure, the cation oxidation state, and the possible defect formation able to maintain the charge neutrality are investigated by spectroscopic (electron paramagnetic resonance (EPR) and micro-Raman), structural (X-ray powder diffraction) and transport (impedance spectroscopy, thermoelectric power) measurements, in the temperature range of 300-1200 K in air and N(2) flow. Starting from the valence state of the doping ions (Fe(3+), Cr(3+), and Mn(2+)), determined by EPR, and from thermoelectric power measurements, evidencing a negative charge transport, different charge-compensating defect equilibria, based on the creation of positive electron holes or oxygen vacancies and electrons, are discussed to interpret the conductivity results.     

Crystal structures of thermoelectric n- and p-type Ba8Ga16Ge30 studied by single crystal, multitemperature, neutron diffraction, conventional X-ray diffraction and resonant synchrotron X-ray diffraction

Comprehensive single-crystal structural investigations of n- and p-type Ba8Ga16Ge30 have been carried out using multitemperature neutron and conventional X-ray diffraction as well as resonant synchrotron X-ray diffraction. The data show that the guest atom positions and dynamics are very similar in the two structures, although the barium atoms are slightly more displaced from the cage centers in the p-type structure than in the n-type structure (Deltad = 0.025 A). For both structures Fourier difference maps calculated from very high-resolution neutron diffraction data (sin theta/lambda > 2 A-1) show that the Ba nuclear density at lowest temperatures (15 K) is distributed in a torus around the crystallographic 6d site with maxima in the 24j positions. At room temperature the maxima have shifted to the 24k position. Analysis of atomic displacement parameters give Einstein temperatures of approximately 60(1) K for both structures. Thus, the fundamental difference in the low temperature thermal conductivity observed for p- and n-type Ba8Ga16Ge30 appear not to be directly related to the guest atom behavior as is commonly assumed in thermoelectric research. The neutron data and the resonant synchrotron X-ray data facilitate refinement of Ga/Ge framework occupancies. The Ga atoms have a clear preference for the 6c site with the preference being somewhat stronger for the n-type structure.     

Characterization of phase transition of Ba2-xSrxIn2O5 by thermal analysis and high temperature X-ray diffraction

The phase transitions of Ba_2-xSr_xIn₂O₅ were investigated with various thermal analyses and high-temperature X-ray diffraction. It was clarified that crystal structure of Ba_2-xSr_xIn₂O₅ with x=0.0~0.4 varies from brownmillerite through distorted perovskite to another distorted perovskite with increase of temperature. The phase transition from brownmillerite to distorted perovskite was revealed to be first order, whereas transition from distorted perovskite to another one was second order. The specimen with x≥0.5 showed only one first order phase transition from brownmillerite to distorted perovskite. The phase diagram of Ba_2-xSr_xIn₂O₅ was established and existence of tricritical point at ~1100°C with x=0.4~0.5 was suggested. This revised version was published online in August 2006 with corrections to the Cover Date.     

Low-temperature Na4Ti5O12 from X-ray and neutron powder diffraction data

The crystal structure of the low-temperature Na₄Ti₅O₁₂ (tetra­sodium penta­titanium dodeca­oxide) phase has been solved and refined from X-ray and neutron powder diffraction data at 295 K. The structure is trigonal, space group P3, with Z = 1, although it is pseudo-centrosymmetric. The O and Na atoms form a distorted close-packed structure, where Ti atoms occupy octahedral sites.     

Zur Kenntnis von Ba10Fe8Pt2Cl2O25

About Ba₁₀Fe₈Pt₂Cl₂O₂₅ The crystal structure of Ba₁₀Fe₈Pt₂Cl₂O₂₅ has been solved by direct methods, using intensity data collected by means of an automatic diffractometer (MoKα). It crystallizes in the hexagonal space group D–P6₃/mmc: a = 5.8034(4) Å, c = 24.997(5) Å, Z = 1. Fe³⁺ ions occur in both octahedral and tetrahedral coordination. Two types of Ba²⁺ ions are formed, with ten and twelve neighbouring atoms. The structure consists of plane connected FeO₆ and PtO₆ octahedra which are connected by corner shared FeO₄ tetrahedra.     

Defect intergrowths in barium polytitanates: 1. Ba2Ti9O20

Using high-resolution transmission electron microscopy, we have investigated the mechanisms of defect formation in samples of the microwave dielectric material, Ba₂Ti₉O₂₀. We found that materials prepared by a variety of different techniques all show considerable structural disorder. The most prevalent intergrowth involved formation of a new triclinic polytype with an ionic arrangement closely related to that in the accepted structure. Defects also resulted from considerable microtwinning and were observed mainly in the samples prepared from a vanadate flux. The degree of nonstoichiometric defect formation was small in comparison to the stoichiometric intergrowths. In this case defects appeared to result from the incorporation of excess vacancies into the close-packed layers of the structure. Barium-deficient surface phases were also formed via a similar mechanism.     

A new perovskite-type compound: Ca4Fe2Ti2O11

A new perovskite-related oxide with a composition Ca₄Fe₂Ti₂O₁₁ has been found in the Ca₂Fe₂O₅-Ca TiO₃ system. Synthesis and characterization by X-ray diffraction and electron microscopy are reported. A model based on a stacking sequence of … OOOTOOOT′ … along theb axis of this material, corresponding to the structure of a compound withn = 4 in theA_nM_nO_3n−1 series, is proposed.     

Structural characterization of Fe/Ti oxide photocatalysts by X-ray,ESR, and Mössbauer methods

The polycrystalline solids TiO₂Fe₂O₃, with iron contents in the range 0–10 at.%, prepared by coprecipitation and by impregnation, and treated in air at temperatures in the range 500–1000°C, have been studied by X-ray, ESR, and Mössbauer methods. The TiO₂ in the samples treated at 800 and 1000°C always forms the rutile phase and the Fe³⁺ has a rather low solubility in it (～0.1 at.%). The Fe³⁺ in excess forms the antiferromagnetic pseudobrookite phase (Fe₂TiO₅). The samples treated at 500 and 650°C show a dependence on the preparation method. Those prepared by coprecipitation give at 500°C the pure anatase phase in which the Fe³⁺ has a higher solubility (≥ 1%); those prepared by impregnation give the anatase phase accompanied by a variable amount of rutile. The treatment at 650°C provokes the partial transformation of anatase to rutile and the complete development of the Fe₂TiO₅ phase. The relevance of these results to the photocatalytic properties shown by these solids for the photoreduction of dinitrogen to ammonia is discussed.