Synthesis and characterization of a NASICON phase of variable composition Na1 − x Ni1 − x Sc1 + x (MoO4)3 (0 ≤ x ≤ 0.5)

Subsolidus phase ratios in the Na₂MoO₄-NiMoO₄-Sc₂(MoO₄)₃ system have been studied using X-ray diffraction, differential thermal analysis, and vibrational spectroscopy. A phase of variable composition Na_{1 ? x} Ni_{1 ? x} Sc_{1 + x} (MoO₄)₃ (0 ≤ x ≤ 0.5) having NASICON structure (space group \(R\bar 3c\) ) and a triple molybdate crystallizing in triclinic system (space group \(P\bar 1\) ) have been obtained. The high conductivity of Na_{1 ? x} Ni_{1 ? x} Sc_{1 + x} (MoO₄)₃ allows the phase of variable composition to be regarded as a promising sodiumion-conductive solid electrolyte.     

Mechanical properties of mixed conducting La0.5Sr0.5Fe1−x Co x O3−δ (0≤x≤1) materials

Young’s modulus, strain–stress behavior, fracture strength, and fracture toughness of (0≤×≤1) materials have been investigated in the temperature range 20–1,000°C. Young’s moduli of and , measured by resonant ultrasound spectroscopy, were 130±1 and 133±3 GPa, respectively. The nonlinear stress–strain relationship observed by four-point bending at room temperature was inferred as a signature of ferroelastic behavior of the materials. Above the ferroelastic to paraelastic transition temperature, the materials showed elastic behavior, but due to high-temperature creep, a nonelastic respond reappeared above ∼800°C. The room temperature fracture strength measured by four-point bending was in the range 107–128 MPa. The corresponding fracture toughness of , measured by single edge V-notch beam method, was 1.16±0.12 MPa·m^1/2. The measured fracture strength and fracture toughness were observed to increase with increasing temperature. The fracture mode changed from intragranular at low temperature to intergranular at high temperature. Tensile stress gradient at the surface of the materials caused by a frozen-in gradient in the oxygen content during cooling was proposed to explain the low ambient temperature fracture strength and toughness.     

Glycolate Ti1 − x Fe x (OCH2CH2O)2 − x/2 as a precursor for the preparation of quasi-one-dimensional (1D) solid solutions Ti1 − x Fe x O2 − 2x/2 (0 ≤ x ≤ 0.1)

Quasi-one-dimensional (1D) solid solutions Ti_{1 ? x} Fe _x (OCH₂CH₂O)_{2 ? x/2} (0 < x ≤ 0.1) with the structure of anatase were prepared by heating the glycolate Ti_{1 ? x} Fe _x (OCH₂CH₂O)_{2 ? x/2} in an atmosphere of air at a temperature of >450°C. The conditions of formation and the properties of the new glycolate Ti₃Fe₂(OCH₂CH₂O)₉ were described. It was found that the synthesized Ti_{1 ? x} Fe _x O_{2 ? 2x/2} solid solutions exhibit photocatalytic activity in the reaction of hydroquinone oxidation in an aqueous solution on irradiation with UV light. A correlation between the rate of oxidation of hydroquinone and the concentration of iron in the catalyst was established. A procedure for the preparation of titanium dioxide with the structure of anatase doped with iron and carbon (Ti_{1 ? x} Fe _x O_{(2 ? x/2) ? yCy)} and also composites on its basis, which contain an excess amount of carbon, was proposed.     

Nonstoichiometry and structural intergrowth in the CaFexMn1−xO3−y (0 ≤ x ≤ 1) system

An electron diffraction and microscopy study of the CaFe_xMn_1−xO_3−y system treated at 1100°C in air has been performed. An increase of y is accompanied by an increase of the cubic perovskite substructure parameter, the nonstoichiometry being accommodated in several ways. The system contains two solid solutions of the perovskite-type (P) and of the brownmillerite-type (B) and also an intermediate phase (x = 0.6) which makes disordered intergrowth with the B-type solid solution. These results are discussed in terms of multitwinning, randomly dispersed oxygen deficiency, and ordered and disordered intergrowth formation.     

Rubidium-cationic conductivity of Rb2−2x Ga2−x A x O4 (A = P, V, Nb, Ta) solid electrolytes

Solid solutions based on rubidium monogallate RbGaO₂ with a general formula Rb_2?2x Ga_2?x A _x O₄ (A = P, V, Nb, and Ta) are synthesized. Their crystal structure and temperature and concentration dependences of conductivity are studied. The highest rubidium-cationic conductivity is (1.8–3.9) × 10^?3 S cm^?1 at 400°C and (1.4–2.1) × 10^?2 S cm^?1 at 700°C. These results are compared with the data for rubidium monogallate doped with four-charged cations and solid solutions based on RbAlO₂.     

Vibrational spectra and electrophysical properties of a NASICON phase of variable composition Na1 − x Co1 − x Sc1 + x (MoO4)3 (0 ≤ x ≤ 0.5)

Subsolidus phase ratios of the Na₂MoO₄-CoMoO₄-Sc₂(MoO₄)₃ system have been studied by X-ray diffraction, differential thermal analysis, and vibrational spectroscopy. A phase of variable composition Na_{1 ? x} Co_{1 ? x} Sc_{1 + x} (MoO₄)₃, 0 ≤ x ≤ 0.5 having NASICON structure (space group \(R\bar 3c\) ) and triple molybdate NaCo₃Sc(MoO₄)₅ crystallizing in triclinic system (space group \(P\bar 1\) ) have been obtained. The high conductivity of Na_{1 ? x} Co_{1 ? x} Sc_{1 + x} (MoO₄)₃ allows the phase of variable composition to be regarded as a promising sodium-ion conducting solid electrolyte.     

Electroconductivity and nature of ion transfer in La1 − x Sr x Sc1 − y Mg y O3 − α system (0.01 ≤ x = y ≤ 0.20) in dry and humid air

The conductivity and ion and proton transfer numbers were measured in La_{1 ? x} Sr _x Sc_{1 ? y} Mg _y O_{3 ? α} system (x = y = 0.10–0.20). The partial conductivities (total ion, proton, oxygen, hole) and their effective activation energies were calculated. The measurements were carried out in air with respect to humidity (pH₂O = 0.04?2.65 kPa) within the temperature range from 630 to 920°C.     

The pillared layered framework of Ba3(In1−xMx)2(HXO4)6 (0≤x≤1; M=Fe,Cr; X=P,As): synthesis,crystal structure,thermal stability and Mössbauer spectroscopy

The hydrothermal synthesis, single crystal structure analysis, spectroscopic and thermal stability studies of the compounds Ba₃(In_1−xM_x)₂(HXO₄)₆ (0≤x≤1; M=Cr, Fe; X=P, As) are reported. The 3D framework of these new phosphates can be described as a pillared layered framework. The metal cations (In³⁺, Fe³⁺, and Cr³⁺) occupy two crystallographically independent octahedral sites, M(1) and M(2). The layers are formed of M(2)O₆ octahedra and (HPO₄) tetrahedra sharing corners, with M(1)O₆ octahedra serving as pillars between adjacent layers. Single crystal study of Ba₃(In_0.5Fe_0.5)(HPO₄)₆ shows that indium and iron segregate between the two metal sites with Fe occupying primarily the site M(1) and In located primarily in M(2) site. Interactions between the building units within the layers occur through hydrogen bonding. Barium cations are located between the pillars, in 8-membered ring tunnels and are coordinated by 12 oxides. The phases loose three water molecules through condensation of six HXO₄ groups to form Ba₂M₂(X₂O₇)₃ at temperatures between 480 and 600 °C. Mössbauer spectroscopy shows the presence of high-spin Fe³⁺ in octahedral coordination.     

Hydrogen content in proton-conducting perovskites CaZr1 − x Sc x O3 − x /2 (x = 0.0–0.2)

The hydrogen content in CaZr_{1 ? x} Sc _x O_{3 ? x/2} (x = 0.00–0.20) and BaZr_0.9Y_0.1O_3-α (for comparison) was studied by powder nuclear microanalysis. The samples were saturated with heavy water (D₂O) vapors at 350 and 400°C in air. The chemical expansion of the CaZr_0.95Sc_0.05O_3-α and BaZr_0.95Y_0.05O_3-α samples at 700°C was measured at different water vapor pressures. A model was suggested to explain the lowered hydrogen content in oxides based on CaZrO₃.     

Multivariate analysis of melting points for homologous series C x H2x − 1NO (x = 3−6)

A multivariate analysis of the empirical structure data for isomeric homologues using principal-component analysis has been carried out, and the correlation with experimental melting points has been shown. Based on the data on the CSD structure, we discuss the impact of molecular H-aggregation.     

New substituted copper titanates with the CaCu3Ti4O12 structure: Li[Cu3−xLix][Ti3−xMV1+x]O12 (MV = Nb: 0.12 ≤ x ≤ 0.33; MV = Ta: x = 0.33)

New substituted copper titanates with the CaCu₃Ti₄O₁₂ perovskite-like structure were synthesized and characterized. Their formula is Li|Cu_3−xLi_x| |Ti_3−xM^V_1+x|O₁₂. There is a homogeneity range for M^V = Nb, 0.12 ≤ x ≤ 0.33, and a unique composition for M^V = Ta, x = 0.33. The unit cell is cubic: a ∼ 2a_p (parameter of the ideal cubic cell) ∼ 7.40 Å. The CaCu₃Ti₄O₁₂-type structure was confirmed from an X-ray powder structural determination. Lithium occupies both square planar sites where it replaces copper and icosahedral sites, with a probable delocalization. Crystal chemistry of the AC₃B₄O₁₂ structure is considered, taking into account the evolution of anion packing and the distortion of polyhedra. A diagrammatic representation is proposed so that precise information on the regularity of the C₃B₄O₁₂ network can be obtained.     

Electron microscopy study of the “cubic” perovskite phase SrFe1−xVxO2.5+x (0.05 ≤ x ≤ 0.1)

The oxygen-deficient “cubic” perovskite phase SrFe_1−xV_xO_2.5+x (0.05 ≤ x ≤ 0.10) quenched from 1473 K has been investigated by electron microscopy. Samples show a microdomain structure composed of ordered grains less than 20 nm. Oxygen vacancies form a brownmillerite-type superlattice in each microdomain, while six orientation variants have been observed within a particle; the oxygen vacancies in one domain are stringed along one of the six possible 〈110〉_C directions of the cubic host lattice. The domain size decreases as x or oxygen content increases. Vacancy arragements within the domains observed in high-resolution lattice images indicate that good structural coherence exists between microdomains and that a basic cubic perovskite skeleton is framed throughout a particle; they also suggest that vacancy content decreases in the boundary regions.     

Synthesis of molecular ferromagnetics [R3R′X]MCr(C2O4)3 (X = N,R = Bun,R′ = Prn,Et, Me; X = P,R = Ph,R′ = Bun; M = Mn,Fe, Co,Ni, Cu)

The synthesis, IR spectra, and the temperatures of the transition into a ferromagnetic state (T _c) of layered ferromagnetics [R₃RX[MCr(C₂O₄)₃ (M = Mn, Fe, Co, Cu, and Ni) with the [Ph₃BuP]⁺, [Bu₃RN]⁺ (R = Pr, Et, and Me) cations capable of subsequently changing the distances between metallooxalate layers have been considered. The temperatureT _c has been found to be independent of the size of the organic cation. It is believed that the determining factors in the transition to a ferromagnetic state are exchange interactions inside the metallooxalate layer.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2327–2330, September, 1996.     

(Sr(1-x)Ba(x))FeO2 (0.4 ≤ x ≤ 1): a new oxygen-deficient perovskite structure

Topochemical reduction of (layered) perovskite iron oxides with metal hydrides has so far yielded stoichiometric compositions with ordered oxygen defects with iron solely in FeO(4) square planar coordination. Using this method, we have successfully obtained a new oxygen-deficient perovskite, (Sr(1-x)Ba(x))FeO(2) (0.4 ≤ x ≤ 1.0), revealing that square planar coordination can coexist with other 3-6-fold coordination geometries. This BaFeO(2) structure is analogous to the LaNiO(2.5) structure in that one-dimensional octahedral chains are linked by planar units, but differs in that one of the octahedral chains contains a significant amount of oxygen vacancies and that all the iron ions are exclusively divalent in the high-spin state. M?ssbauer spectroscopy demonstrates, despite the presence of partial oxygen occupations and structural disorders, that the planar-coordinate Fe(2+) ions are bonded highly covalently, which accounts for the formation of the unique structure. At the same time, a rigid 3D Fe-O-Fe framework contributes to structural stabilization. Powder neutron diffraction measurements revealed a G-type magnetic order with a drastic decrease of the Néel temperature compared to that of SrFeO(2), presumably due to the effect of oxygen disorder/defects. We also performed La substitution at the Ba site and found that the oxygen vacancies act as a flexible sink to accommodate heterovalent doping without changing the Fe oxidation and spin state, demonstrating the robustness of this new structure against cation substitution.     

Homoleptic diphosphacyclobutadiene complexes [M(η(4)-P2C2R2)2]x- (M = Fe, Co; x = 0, 1)

The preparation and comprehensive characterization of a series of homoleptic sandwich complexes containing diphosphacyclobutadiene ligands are reported. Compounds [K([18]crown-6)(thf)(2)][Fe(η(4)-P(2)C(2)tBu(2))(2)] (K1), [K([18]crown-6)(thf)(2)][Co(η(4)-P(2)C(2)tBu(2))(2)] (K2), and [K([18]crown-6)(thf)(2)][Co(η(4)-P(2)C(2)Ad(2))(2)] (K3, Ad = adamantyl) were obtained from reactions of [K([18]crown-6)(thf)(2)][M(η(4)-C(14)H(10))(2)] (M = Fe, Co) with tBuC[triple bond]P (1, 2), or with AdC[triple bond]P (3). Neutral sandwiches [M(η(4)-P(2)C(2)tBu(2))(2)] (4: M = Fe 5: M = Co) were obtained by oxidizing 1 and 2 with [Cp(2)Fe]PF(6). Cyclic voltammetry and spectro-electrochemistry indicate that the two [M(η(4)-P(2)C(2)tBu(2))(2)](-)/[M(η(4)-P(2)C(2)tBu(2))(2)] moieties can be reversibly interconverted by one electron oxidation and reduction, respectively. Complexes 1-5 were characterized by multinuclear NMR, EPR (1 and 5), UV/Vis, and M?ssbauer spectroscopies (1 and 4), mass spectrometry (4 and 5), and microanalysis (1-3). The molecular structures of 1-5 were determined by using X-ray crystallography. Essentially D(2d)-symmetric structures were found for all five complexes, which show the two 1,3-diphosphacyclobutadiene rings in a staggered orientation. Density functional theory calculations revealed the importance of covalent metal-ligand π bonding in 1-5. Possible oxidation state assignments for the metal ions are discussed.     

Synthesis and crystal structure of Mo6−x Nb x I11 (x = 1–1.5)

A solid solution Mo_{6 ? x} Nb _x I₁₁ (x = 1.1–1.5) containing cluster cores {Mo₅NbI₈} is obtained by the high-temperature reaction of molybdenum, niobium, and iodine (550°C, 70 h, quartz ampule). According to the X-ray diffraction data, heating at 800°C in a molybdenum container results in the decomposition of the solution to Mo₆I₁₂ and Nb₆I₁₁. According to the X-ray structure analysis data, the compounds are isostructural to the high-spin modification Nb₆I₁₁ (space group Pccn). The presence of Nb atoms in the structure changes the structural type from the layered (Mo₆I₁₂) to framework structure, noticeably increases the metalmetal distances (2.661–2.716 Å, 2.695 Å) Mo₆ octahedron with the retention of the distance from the metal (M) to the μ₃-“capped” I atoms, and strongly elongates the M₆-I-M₆ bridges almost to the value observed in Nb₆I₁₁.     

X-ray photoelectron spectroscopy investigation of perovskites La1−x Sr x FeO3−y (0 ≤x < 1.0), prepared via a mechanochemical route

Perovskite-structure oxides La_1?x Sr _x FeO_3?y (x = 0, 0.2, 0.6, 1) were synthesized by the mechanochemical method. In order to refine the stoichiometric composition and the charge state of ions, these samples were studied by X-ray photoelectron spectroscopy (XPS). An investigation of perovskites with x = 0, 0.2, and 0.6 in air at room temperature showed that these samples do not contain oxygen vacancies (y = 0), i.e., they are fully oxidized. Hence, to produce electrical neutrality, these samples should contain iron(4+) cations in an amount proportional to the degree of substitution (x) of strontium(2+) for lanthanum(3+). However, no Fe⁴⁺ cations were found in the oxides. All perovskites contain only Fe³⁺ cations, oxygen ions O^2? along with oxygen ions with reduced electron density (O^?). These data provid evidence of the possible electron density redistribution from oxygen ions to iron cations. The fact that the oxides contain oxygen ions with reduced electron density suggests that weakly bound lattice oxygen in substituted perovskites is represented by O^? ions.     

Synthesis and properties of fuel cell anodes based on (La0.5 + x Sr0.5 − x )1 − y Mn0.5Ti0.5O3 − δ (x = 0–0.25, y = 0–0.03)

Results are presented of studying electrochemical properties of perovskite-like solid solutions (La_{0.5 + x} Sr_{0.5 ? x} )_{1 ? y} Mn_0.5Ti_0.5O_{3 ? δ} (x = 0–0.25, y = 0–0.03) synthesized using the citrate technique and studied as oxide anodic materials for solid oxide fuel cells (SOFC). X-ray diffraction (XRD) analysis is used to establish that the materials are stable in a wide range of oxygen chemical potential, stable in the presence of 5 ppm H₂S in the range of intermediate temperatures, and also chemically compatible with the solid electrolyte of La_0.8Sr_0.2Ga_0.8Mg_0.15Co_0.05O_{3 ? δ} (LSGMC). It is shown that transition to a reducing atmosphere results in a decrease in electron conductivity that produced a significant effect on the electrochemical activity of porous electrodes. Model cells of planar SOFC on a supporting solid-electrolyte membrane (LSGMC) with anodes based on (La_0.6Sr_0.4)_0.97Mn_0.5Ti_0.5O_{3 ? δ} and (La_0.75Sr_0.25)_0.97Mn_0.5Ti_0.5O_{3 ? δ} and a cathode of Sm_0.5Sr_0.5CoO_{3 ? δ} are manufactured and tested using the voltammetry technique.     

ChemInform Abstract: (Sr1-xBax)FeO2 (0.4 ≤ x ≤ 1): A New Oxygen-Deficient Perovskite Structure.

The new oxygen-deficient perovskites of title are prepared by reaction of (Sr_1-xBa_x)FeO_3-δ (x = 0.4, 0.5, 0.6, 0.7, 0.8, 0.9; δ ≤ 0.5; obtained from stoichiometric mixtures of SrCO₃, BaCO₃, and Fe₂O₃ at 1473 K in air for 48 h) with an excess of CaH₂ at 593 K for 3—14 d (0.4 ≤ x ≤ 0.9) and NaH at 413 K for 3 d (x = 1.0).