Magnetic diphase nanostructure of ZnFe2O4/γ-Fe2O3

Magnetic diphase nanostructures of ZnFe₂O₄/γ-Fe₂O₃ were synthesized by a solvothermal method. The formation reactions were optimized by tuning the initial molar ratios of Fe/Zn. All samples were characterized by X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and Raman spectra. It is found that when the initial molar ratio of Fe/Zn is larger than 2, a diphase magnetic nanostructure of ZnFe₂O₄/γ-Fe₂O₃ was formed, in which the presence of ZnFe₂O₄ enhanced the thermal stability of γ-Fe₂O₃. Further increasing the initial molar ratio of Fe/Zn larger than 6 destabilized the diphase nanostructure and yielded traces of secondary phase α-Fe₂O₃. The grain surfaces of diphase nanostructure exhibited a spin-glass-like structure. At room temperature, all diphase nanostructures are superparamagnetic with saturation magnetization being increased with γ-Fe₂O₃ content.     

Non-centrosymmetric Ba3Ti3O6(BO3)2

The compound previously reported as Ba₂Ti₂B₂O₉ has been reformulated as Ba₃Ti₃B₂O₁₂, or Ba₃Ti₃O₆(BO₃)₂, a new barium titanium oxoborate. Small single crystals have been recovered from a melt with a composition of BaTiO₃:BaTiB₂O₆ (molar ratio) cooled between 1100°C and 850°C. The crystal structure has been determined by X-ray diffraction: hexagonal system, non-centrosymmetric space group, a=8.7377(11) Å, c=3.9147(8) Å, Z=1, wR(F²)=0.039 for 504 unique reflections. Ba₃Ti₃O₆(BO₃)₂ is isostructural with K₃Ta₃O₆(BO₃)₂. Preliminary measurements of nonlinear optical properties on microcrystalline samples show that the second harmonic generation efficiency of Ba₃Ti₃O₆(BO₃)₂ is equal to 95% of that of LiNbO₃.     

Effect of capping and particle size on Raman laser-induced degradation of γ-Fe2O3 nanoparticles

Diol capped γ-Fe₂O₃ nanoparticles are prepared from ferric nitrate by refluxing in 1,4-butanediol (9.5 nm) and 1,5-pentanediol (15 nm) and uncapped particles are prepared by refluxing in 1,2-propanediol followed by sintering the alkoxide formed. X-ray diffraction (XRD) shows that all the samples have the spinel phase. Raman spectroscopy shows that the samples prepared in 1,4-butanediol and 1,5-pentanediol and 1,2-propanediol (sintered at 573 and 673 K) are γ-Fe₂O₃ and the 773 K-sintered sample is Fe₃O₄. Raman laser studies carried out at various laser powers show that all the samples undergo laser-induced degradation to α-Fe₂O₃ at higher laser power. The capped samples are however, found more stable to degradation than the uncapped samples. The stability of γ-Fe₂O₃ sample with large particle size (15.4 nm) is more than the sample with small particle size (10.2 nm). Fe₃O₄ having a particle size of 48 nm is however less stable than the smaller γ-Fe₂O₃ nanoparticles.     

On the ammonolysis of Ga2O3: An XRD, neutron diffraction and XAS investigation of the oxygen-rich part of the system Ga2O3-GaN

We investigated the ammonolysis of β-Ga₂O₃ at elevated temperatures by means of ex situ X-ray diffraction, ex situ neutron diffraction and in situ X-ray absorption spectroscopy. Within the detection limits of these methods, we can rule out the existence of a crystalline or amorphous oxynitride phase that is not derived from wurtzite-type GaN. No evidence for a β-Ga₂O₃ related oxynitride phase was found, and the nitrogen solubility in β-Ga₂O₃ was found to be below the detection limit of about 2-3 at% in the anionic sublattice. These findings were obtained by monitoring the anionic occupancy factors and the lattice parameters of the β-Ga₂O₃ phase obtained from total diffraction pattern refinement with the Rietveld method and by linear combination fitting of the X-ray absorption spectra that were recorded during the ammonolysis.     

Phase relations, crystal chemistry, and dielectric properties in sections of the La2O3-CaO-MgO-TiO2 system

Subsolidus phase equilibria and crystal chemistry were studied for the La₂O₃-MgO-TiO₂ system and for the ternary sections LaMg_1/2Ti_1/2O₃-CaTiO₃-La₂O₃ and LaMg_1/2Ti_1/2O₃-CaTiO₃-La_0.833Mg_0.25Ti_0.75O₃ in the quaternary La₂O₃-CaO-MgO-TiO₂ system. Dielectric properties (relative permittivity and temperature coefficient of resonant frequency, τ_f) were measured at 5-10 GHz and mapped onto the phase equilibria relations to reveal the compositions of temperature-stable (τ_f=0) compounds and mixtures. Phase equilibria relations were obtained by X-ray powder diffraction analysis of approximately 80 specimens prepared by solid-state reactions in air at ∼1450°C. Six ternary phases were found to form in the La₂O₃-MgO-TiO₂ system, including the three previously reported compounds LaMg_1/2Ti_1/2O₃, La₅Mg_0.5Ti_3.5O₁₅, and “La₆MgTi₄O₁₈”; and the new phases La₁₀MgTi₉O₃₄, La₉Mg_0.5Ti_8.5O₃₁, and a perovskite-type solid solution (1−x)LaMg_1/2Ti_1/2O₃-xLa_2/3TiO₃ (0?x?0.5). The phase previously reported as “La₆MgTi₄O₁₈” was found to form off-composition, apparently as a point compound, at La₆Mg_0.913Ti_4.04O₁₈. Indexed experimental X-ray powder diffraction patterns are given for LaMg_1/2Ti_1/2O₃, La₅Mg_0.5Ti_3.5O₁₅, La₆Mg_0.913Ti_4.04O₁₈, La₁₀MgTi₉O₃₄, and La₉Mg_0.5Ti_8.5O₃₁. LaMg_1/2Ti_1/2O₃ exhibits a slightly distorted perovskite structure with ordered B-cations (P2₁/n; a=5.5608(2) Å, b=5.5749(3) Å, c=7.8610(5) Å, β=90.034(4)°). La₅Mg_0.5Ti_3.5O₁₅ (Pm1; a=5.5639(1), c=10.9928(5) Å) and La₆Mg_0.913Ti_4.04O₁₈ (R3m; a=5.5665(1), c=39.7354(9) Å) are n=5 and n=6 members, respectively, of the (111) perovskite-slab series A_nB_n−1O_3n. The new phases La₁₀MgTi₉O₃₄ (a=5.5411(2), b=31.3039(9), c=3.9167(1) Å) and La₉Mg_0.5Ti_8.5O₃₁ (a=5.5431(2), b=57.055(1), c=3.9123(1) Å) are n=5 and n=4.5 members, respectively, of the (110) perovskite-slab series A_nB_nO_3n+2, which exhibit orthorhombic subcells; electron diffraction revealed monoclinic superlattices with doubled c-parameters for both compounds. Extensive perovskite-type solid solutions form in the ternary sections LaMg_1/2Ti_1/2O₃-CaTiO₃-La₂O₃ and LaMg_1/2Ti_1/2O₃-CaTiO₃-La_0.833Mg_0.25Ti_0.75O₃. The La₂O₃-MgO-TiO₂ system contains two regions of temperature-stable (τ_f=0) compositions. The quaternary La₂O₃-CaO-MgO-TiO₂ system contains an extensive single-phase perovskite-type volume through which passes a surface of temperature-stable compositions with permittivities projected to be in the 40-50 range. Traces of this surface occur as lines of τ_f=0 perovskite-type phases in the ternary sections LaMg_1/2Ti_1/2O₃-CaTiO₃-La₂O₃ and LaMg_1/2Ti_1/2O₃-CaTiO₃-La_0.833Mg_0.25Ti_0.75O₃.     

Structural and electrical properties of the 2Bi2O3·3ZrO2 system

Powder mixtures of α-Bi₂O₃ (bismite) and monoclinic m-ZrO₂ (baddeleyite) in the molar ratio 2:3 were mechanochemically and thermally treated with the goal to examine the phases, which may appear during such procedures. The prepared samples were characterized by X-ray powder diffraction, differential scanning calorimetry (DSC), electrical measurements, as well as scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mechanochemical reaction leads to the gradual formation of a nanocrystalline phase, which resembles δ-Bi₂O₃, a high-temperature Bi₂O₃ polymorph. Isothermal sintering in air at a temperature of 820 °C for 24 h followed by quenching to room temperature yielded a mixture of ZrO₂-stabilized β-Bi₂O₃ and m-ZrO₂ phases, whereas in slowly cooled products, the complete separation of the initial α-Bi₂O₃ and m-ZrO₂ constituents was observed. The dielectric permittivity of the sintered samples significantly depended on the temperature. The sintered and quenched samples exhibited a hysteresis dependence of the dielectric shift, showing that the ZrO₂-doped β-Bi₂O₃ phase possess ferroelectric properties, which were detected for the first time. This fact, together with Rietveld refinement of the β-Bi₂O₃/m-ZrO₂ mixture based on neutron powder diffraction data showed that ZrO₂-doped β-Bi₂O₃ has a non-centrosymmetric structure with as the true space group. The ZrO₂ content in the doped β-Bi₂O₃ and the crystal chemical reasons for the stabilization of the β-Bi₂O₃ phase by the addition of m-ZrO₂ are discussed.     

The formation and physicochemical characterization of Al2O3-doped manganese ferrites

Mn/Fe mixed oxide solids doped with Al₂O₃ (0.32-1.27 wt.%) were prepared by impregnation of manganese nitrate with finely powdered ferric oxide, then treated with different amounts of aluminum nitrate. The obtained samples were calcined in air at 700-1000 °C for 6 h. The specific surface area (S_BET) and the catalytic activity of pure and doped precalcined at 700-1000 °C have been measured by using N₂ adsorption isotherms and CO oxidation by O₂. The structure and the phase changes were characterized by DTA and XRD techniques. The obtained results revealed that Mn₂O₃ interacted readily with Fe₂O₃ to produce well-crystallized manganese ferrite (MnFe₂O₄) at temperatures of 800 °C and above. The degree of propagation of this reaction increased by Al₂O₃-doping and also by increasing the heating temperature. The treatment with 1.27 wt.% Al₂O₃ followed by heating at 1000 °C resulted in complete conversion of Mn/Fe oxides into the corresponding ferrite phase. The catalytic activity and S_BET of pure and doped solids were found to decrease, by increasing both the calcination temperature and the amount of Al₂O₃ added, due to the enhanced formation of MnFe₂O₄ phase which is less reactive than the free oxides (Mn₂O₃ and Fe₂O₃). The activation energy of formation (ΔE) of MnFe₂O₄ was determined for pure and doped solids. The promotion effect of aluminum in formation of MnFe₂O₄ was attributed to an effective increase in the mobility of reacting cations.     

Phase formation, crystal chemistry, and properties in the system Bi2O3-Fe2O3-Nb2O5

Subsolidus phase relations have been determined for the Bi₂O₃-Fe₂O₃-Nb₂O₅ system in air (900-1075 °C). Three new ternary phases were observed—Bi₃Fe_0.5Nb_1.5O₉ with an Aurivillius-type structure, and two phases with approximate stoichiometries Bi₁₇Fe₂Nb₃₁O₁₀₆ and Bi₁₇Fe₃Nb₃₀O₁₀₅ that appear to be structurally related to Bi₈Nb₁₈O₅₇. The fourth ternary phase found in this system is pyrochlore (A₂B₂O₆O′), which forms an extensive solid solution region at Bi-deficient stoichiometries (relative to Bi₂FeNbO₇) suggesting that ≈4-15% of the A-sites are occupied by Fe³⁺. X-ray powder diffraction data confirmed that all Bi-Fe-Nb-O pyrochlores form with positional displacements, as found for analogous pyrochlores with Zn, Mn, or Co instead of Fe. A structural refinement of the pyrochlore 0.4400:0.2700:0.2900 Bi₂O₃:Fe₂O₃:Nb₂O₅ using neutron powder diffraction data is reported with the A cations displaced (0.43 Å) to 96g sites and O′ displaced (0.29 Å) to 32e sites (Bi_1.721Fe_0.190(Fe_0.866Nb_1.134)O₇, Fd3¯m (#227), ). This displacive model is somewhat different from that reported for Bi_1.5Zn_0.92Nb_1.5O_6.92, which exhibits twice the concentration of small B-type cations on the A-sites as the Fe system. Bi-Fe-Nb-O pyrochlores exhibited overall paramagnetic behavior with large negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. The single-phase pyrochlore with composition Bi_1.657Fe_1.092Nb_1.150O₇ exhibited low-temperature dielectric relaxation similar to that observed for Bi_1.5Zn_0.92Nb_1.5O_6.92; at 1 MHz and 200 K the relative permittivity was 125, and above 350 K conductive effects were observed.     

Characterization and evaluation of Fe2O3/Al2O3 oxygen carrier prepared by sol–gel combustion synthesis

The sol-gel combustion synthesis (SGCS) for oxygen carrier (OC) to be used in chemical looping combustion (CLC) was first designed and experimented in this work, which is a new method of OC synthesis by combining sol-gel technique and solution combustion synthesis. Cheap hydrated metal nitrates and urea were adopted as precursors to prepare Fe₂O₃/Al₂O₃ OC at the molar ratio to unity (Fe1Al1), which was characterized through various means, including Fourier transforms infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray diffractor (XRD), and N₂ isothermal adsorption/desorption method. FTIR analysis on the chemical structure of the dried gel of Fe1Al1 indicated that urea was partly hydrolyzed and the hydrated basic carbonate was formed by the combination of groups such as (Fe(_1−yAl_y)_1−xO_1−3x, CO₃²⁻ and -OH-. By analyzing the staged products during SGCS, calcination was found as a necessary step to produce Fe₂O₃/Al₂O₃ OC with separate phases of α-Fe₂O₃ and α-Al₂O₃. Through TGA-DTA, the decomposition of the dried gel was found to undergo five stages. The analysis of the evolved gases from the gel decomposition using FTIR partially confirmed the staged decomposition and assisted a better understanding of the mechanism of SGCS. XRD identification further substantiated the necessity of calcination to synthesize Fe₂O₃/Al₂O₃ OC with separate phases of α-Fe₂O₃ and α-Al₂O₃, though it was not necessary for the synthesis of single phase α-Fe₂O₃ and α-Al₂O₃. Structural characterization performed on N₂ adsorption analyzer displayed that the pore shape of Fe1Al1 particles was heterogeneous. Finally, H₂ temperature-programmed reduction (TPR) of Fe1Al1 products in TGA indicated that the reduction reaction of Fe1Al1 OC after calcination was a single step reaction from α-Fe₂O₃ to Fe, and calcination benefited to improve the transfer rate of the lattice oxygen from the OC to fuel H₂. Furthermore, four times of reduction and oxidization (redox) reaction by alternating with H₂ and air demonstrated the synthesized OC had good reactivity and sintering-resistance, much suitable to be used in the realistic CLC. Overall, the SGCS method was found superior to other existent methods to prepare Fe₂O₃/Al₂O₃ OC for CLC application.     

Synthesis and characterization of n=5, 6 members of the La4Srn−4TinO3n+2 series with layered structure based upon perovskite

Layered compounds have been synthesized and structurally characterized for the n=5 and 6 members of the perovskite-related family La₄Sr_n−4Ti_nO_3n+2 by combining X-ray diffraction and transmission electron microscopy. Their structure can be regarded as comprising [(La,Sr)₅Ti₅O₁₇] and [(La,Sr)₆Ti₆O₂₀] perovskite blocks joined by crystallographic shears along the a-axis, with consecutive blocks shifted by 1/2 [100]_p. The n=5 member is similar to the previously reported n=5 member of other A_nB_nO_3n+2-related series. The n=6 member, which has only been briefly reported in other systems previously, is also a well-behaved member of this A_nB_nO_3n+2 series.     

Structure and magnetic properties of the orthorhombic n=2 Ruddlesden-Popper phases Sr3Co2O5+δ (δ=0.91, 0.64 and 0.38)

The reduced Ruddlesden-Popper phases, Sr₃Co₂O_5+δ with δ=0.91, 0.64 and 0.38, have been prepared in a nitrogen atmosphere. The crystal structures were determined by powder neutron diffraction. Oxygen vacancies are found both in O(3) and O(4) sites but the majority are along one crystallographic axis in the CoO₂ plane, inducing an orthorhombic distortion of the normally tetragonal n=2 Ruddelsden-Popper structure. Superstructures due to oxygen ordering are observed by electron microscopy. The magnetic measurements reveal complex behavior with some ferromagnetic interactions present for Sr₃Co₂O_5.91 and Sr₃Co₂O_5.64.     

Synthesis and nonlinear optical properties of BaTi(BO3)2 and Ba3Ti3O6(BO3)2 crystals in glasses with high TiO2 contents

The ternary BaO-TiO₂-B₂O₃ glasses containing a large amount of TiO₂ (20-40 mol%) are prepared, and their optical basicities (Λ), the formation, structural features and second-order optical nonlinearities of BaTi(BO₃)₂ and Ba₃Ti₃O₆(BO₃)₂ crystals are examined to develop new nonlinear optical materials. It is found that the glasses with high TiO₂ contents of 30-40 mol% show large optical basicities of Λ=0.81-0.87, suggesting the high polarizabity of TiO_n polyhedra (n=4-6) in the glasses. BaTi(BO₃)₂ and Ba₃Ti₃O₆(BO₃)₂ crystals are found to be formed as main crystalline phases in the glasses. It is found that BaTi(BO₃)₂ crystals tend to orient at the surface of crystallized glasses. The new XRD pattern for the Ba₃Ti₃O₆(BO₃)₂ phase is proposed through Rietvelt analysis. The second harmonic intensities of crystallized glasses were found to be 0.8 times as large as α-quartz powders, i.e., I^2ω(sample)/I^2ω(α-quartz)=0.8, for the sample with BaTi(BO₃)₂ crystals and to be I^2ω(sample)/I^2ω(α-quartz)=68 for the sample with Ba₃Ti₃O₆(BO₃)₂ crystals. The Raman scattering spectra for these two crystalline phases are measured for the first time and their structural features are discussed.     

Crystal growth, structure determination, and optical properties of new potassium-rare-earth silicates K3RESi2O7 (RE=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu)

Single crystals of K₃RESi₂O₇ (RE=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were grown from a potassium fluoride flux. Two different structure types were found for this series. Silicates containing the larger rare earths, RE=Gd, Tb, Dy, Ho, Er, Tm, Yb crystallize in a structure K₃RESi₂O₇ that contains the rare-earth cation in both a slightly distorted octahedral and an ideal trigonal prismatic coordination environment, while in K₃LuSi₂O₇, containing the smallest of the rare earths, lutetium is found solely in an octahedral coordination environment. The structure of K₃LuSi₂O₇ crystallizes in space group P6₃/mmc with a=5.71160(10) Å and c=13.8883(6) Å. The structures containing the remaining rare earths crystallize in the space group P6₃/mcm with the lattice parameters of a=9.9359(2) Å, c=14.4295(4) Å, (K₃GdSi₂O₇); a=9.88730(10) Å, c=14.3856(3) Å, (K₃TbSi₂O₇); a=9.8673(2) Å, c=14.3572(4) Å, (K₃DySi₂O₇); a=9.8408(3) Å, c=14.3206(6) Å, (K₃HoSi₂O₇); a=9.82120(10) Å, c=14.2986(2) Å, (K₃ErSi₂O₇); a=9.80200(10) Å, c=14.2863(4) Å, (K₃TmSi₂O₇); a=9.78190(10) Å, c=14.2401(3) Å, (K₃YbSi₂O₇). The optical properties of the silicates were investigated and K₃TbSi₂O₇ was found to fluoresce in the visible.     

Ion-beam irradiation of lanthanum compounds in the systems La2O3-Al2O3 and La2O3-TiO2

Thin crystals of La₂O₃, LaAlO₃, La_2/3TiO₃, La₂TiO₅, and La₂Ti₂O₇ have been irradiated in situ using 1 MeV Kr²⁺ ions at the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), Argonne National Laboratory (ANL). We observed that La₂O₃ remained crystalline to a fluence greater than 3.1×10¹⁶ ions cm⁻² at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline-amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (T_c) of 647 K for LaAlO₃, 840 K for La₂Ti₂O₇, 865 K for La_2/3TiO₃, and 1027 K for La₂TiO₅. The T_c values observed in this study, together with previous data for Al₂O₃ and TiO₂, are discussed with reference to the melting points for the La₂O₃-Al₂O₃ and La₂O₃-TiO₂ systems and the different local environments within the four crystal structures. Results suggest that there is an observable inverse correlation between T_c and melting temperature (T_m) in the two systems. More complex relationships exist between T_c and crystal structure, with the stoichiometric perovskite LaAlO₃ being the most resistant to amorphisation.     

Interactions of Ba2YCu3O6+y with the Gd3NbO7 buffer layer in coated conductors

A systematic study of the chemical interaction of Ba₂YCu₃O_6+y and Gd₃NbO₇ was conducted under two processing conditions: purified air (21% p_o2), and 100 Pa p_o2 (0.1% p_o2). Phases present along the pseudo-binary join Ba₂YCu₃O_6z and Gd₃NbO₇ were found to be in two five-phase volumes within the system. Three common phases that are present in all samples are (Y,Gd)₂Cu₂O₅, Ba(Y,Gd)₂CuO₅ and Cu₂O or CuO (depending on the processing conditions). The assemblies of phases can be categorized in three regions, with Ba₂YCu₃O_6+y: Gd₃NbO₇ ratios of (I)<5.5:4.5; (II)=5.5:4.5; and (III)>5.5:4.5. The lowest melting temperature of the system was determined to be ≈938 °C in air, and 850 °C at 100 Pa p_o2. Structure determinations of two selected phases, Ba₂(Gd_xY_1−x)NbO₆ (Fm3¯m, No. 225), and (Gd_xY_3−x)NbO₇ (C222₁, No. 20 and Ccmm, No. 63), were completed using the X-ray Rietveld refinement technique. Reference X-ray powder diffraction patterns for selected phases of Ba₂(Gd_xY_1−x)NbO₆ (x=0.2, 0.4, 0.6, and 0.8) and (Gd_xY_3−x)NbO₇ (x=0.6, 1.2, 1.8, 2.4 and 3) have been prepared for inclusion in the Powder Diffraction File (PDF).     

Sol-gel synthesized semiconducting LaCo0.8Fe0.2O3-based powder for thick film NH3 gas sensor

Perovskite type LaCo_xFe_1−xO₃ nanoparticles was synthesized by a sol-gel citrate method. The structural, electrical and sensing characteristics of the LaCo_xFe_1−xO₃ system were investigated. The structural characteristics were performed by using X-ray diffraction (XRD) and transmission electron microscopy (TEM) to examine the phase and morphology of the resultant powder. The XRD pattern shows nanocrystalline solid solution of LaCo_xFe_1−xO₃ with perovskite phase. Electrical properties of synthesized nanoparticles are studied by DC conductivity measurement. The sensor shows high response towards ammonia gas in spite of other reducing gases when x = 0.8. The effect of 0.3 wt.% Pd-doped LaCo_0.8Fe_0.2O₃ on the response and a recovery time was also addressed.     

Thermal stability and crystal structure of β-Ba3YB3O9

A new compound, β-Ba₃YB₃O₉, has been attained through solid phase transition from α-Ba₃YB₃O₉ at high temperatures. Differential thermal analysis (DTA) revealed the phase transition at about 1120°C, the melting temperature at about 1253°C. Its crystal structure has been determined from powder X-ray diffraction data. The refinement was carried out using the Rietveld method and the final refinement converged with R_p=10.5% and R_wp=13.7%. This compound belongs to the hexagonal space group R-3, with lattice parameters a=13.0441(1) Å and c=9.5291(1) Å. There are 6 formulas per unit cell and 7 atoms in the asymmetric unit. The structure of β-Ba₃YB₃O₉ is built up from Ba(Y)O₈, BaO₆ and YB₆O₁₈ units formed by one YO₆ octahedron and six BO₃ triangles with shared O atoms.     

Crystal growth of a novel oxygen-deficient layered perovskite: Ba7Li3Ru4O20

Single crystals of both Ba₇Li₃Ru₄O₂₀ and Ba₄NaRu₃O₁₂ were grown from reactive molten hydroxide fluxes. Ba₇Li₃Ru₄O₂₀ is a 7L-layer perovskite-related phase resulting from the stacking of six [AO₃] layers and one oxygen deficient [AO₂] layer, thereby creating LiO₄ tetrahedra in addition to the LiO₆ octahedra and face-sharing Ru₂O₉ bi-octahedra formed from the [AO₃] layers. The compound crystallizes in the space group with a=5.7927(1) Å and c=50.336(2) Å, Z=3. Ba₄NaRu₃O₁₂ crystallizes in the space group P6₃mc with lattice parameters of a=5.8014(2) Å and c=19.2050(9) Å, Z=2. Ba₄NaRu₃O₁₂ is identical to a previously reported neutron refinement structure. The magnetic properties of Ba₇Li₃Ru₄O₂₀ are also reported.     

Sol-gel synthesis of K3InF6 and structural characterization of K2InC10O10H6F9, K3InC12O14H4F18 and K3InC12O12F18

K₃InF₆ is synthesized by a sol-gel route starting from indium and potassium acetates dissolved in isopropanol in the stoichiometry 1:3, with trifluoroacetic acid as fluorinating agent. The crystal structures of the organic precursors were solved by X-ray diffraction methods on single crystals. Three organic compounds were isolated and identified: K₂InC₁₀O₁₀H₆F₉, K₃InC₁₂O₁₄H₄F₁₈ and K₃InC₁₂O₁₂F₁₈. The first one, deficient in potassium in comparison with the initial stoichiometry, is unstable. In its crystal structure, acetate as well as trifluoroacetate anions are coordinated to the indium atom. The two other precursors are obtained, respectively, by quick and slow evaporation of the solution. They correspond to the final organic compounds, which give K₃InF₆ by decomposition at high temperature. The crystal structure of K₃InC₁₂O₁₄H₄F₁₈ is characterized by complex anions [In(CF₃COO)₄(OH_x)₂]^(5−2x)− and isolated [CF₃COOH_2−x]^(x−1)− molecules with x=2 or 1, surrounded by K⁺ cations. The crystal structure of K₃InC₁₂O₁₂F₁₈ is only constituted by complex anions [In(CF₃COO)₆]³⁻ and K⁺ cations. For all these compounds, potassium cations ensure only the electroneutrality of the structure. IR spectra of K₂InC₁₀O₁₀H₆F₉ and K₃InC₁₂O₁₂F₁₈ were also performed at room temperature on pulverized crystals.     

Co3−δO4 paracrystal: 3D assembly of nanosize defect clusters in spinel lattice

Paracrystalline array of defect clusters ca. five times the lattice spacing of the average Co_3−δO₄ spinel structure occurred more or less in a relaxed manner when the sintered Co_1−xO polycrystals were air-quenched below the Co_1−xO/Co_3−δO₄ transition temperature to activate oxy-precipitation of cube-like Co_3−δO₄ at dislocations. The same paracrystalline spacing was obtained for Co_3−δO₄ when formed via oxidizing/sintering the Co_1−xO powders at 800°C in air, suggesting a nearly constant δ value for Co_3−δO₄ in the T-P_O2 conditions encountered. The extra cobalt vacancies and Co³⁺ interstitials, as a result of δ value, may form additional 4:1-derived defect clusters for further paracrystalline distribution in the spinel lattice. The nanosize defect clusters self-assembled by columbic interactions and lattice relaxation in ionic crystal may have potential applications as step-wise sensor of oxygen partial pressure at high temperatures.