Phase evolution, phase transition, raman spectra, infrared spectra, and microwave dielectric properties of low temperature firing (K(0.5x)Bi(1-0.5x))(Mo(x)V(1-x))O4 ceramics with scheelite related structure

In the present work, the (K(0.5x)Bi(1-0.5x))(Mo(x)V(1-x))O(4) ceramics (0≤x ≤ 1.00) were prepared via the solid state reaction method and sintered at temperatures below 830 °C. At room temperature, the BiVO(4) scheelite monoclinic solid solution was formed in ceramic samples with x < 0.10. When x lies between 0.1-0.19, a BiVO(4) scheelite tetragonal phase was formed. The phase transition from scheelite monoclinic to scheelite tetragonal phase is a continuous, second order ferroelastic transition. High temperature X-ray diffraction results showed that this phase transition can also be induced at high temperatures about 62 °C for x = 0.09 sample, and has a monoclinic phase at room temperature. Two scheelite tetragonal phases, one being a BiVO(4) type and the other phase is a (K,Bi)(1/2)MoO(4) type, coexist in the compositional range 0.19 < x < 0.82. A pure (K,Bi)(1/2)MoO(4) tetragonal type solid solution can be obtained in the range 0.82 ≤ x ≤ 0.85. Between 0.88 ≤ x ≤ 1.0, a (K,Bi)(1/2)MoO(4) monoclinic solid solution region was observed. Excellent microwave dielectric performance with a relative dielectric permittivity around 78 and Qf value above 7800 GHz were achieved in ceramic samples near the ferroelastic phase boundary (at x = 0.09 and 0.10).     

A study of the phase behaviour of metal-free phthalocyanine in a differential scanning calorimeter

The phase behaviour of metal-free phthalocyanine (H₂Pc) has been studied in a differential scanning calorimeter. The effect of the thermal history of samples on the DSC curves was investigated to obtain data concerning the phase transition which appeared on α as well as β forms of H₂Pc over the termperature range from 250 to 340 K. To characterize the α metal-free phthalocyanine at low temperatures, the capacitance of an Ag(H₂Pc)Al sandwich was measured as a function of the temperature. The specific heats of the α and β forms of H₂Pc and the heat of the α → β polymorphic transition were measured. Kinetic parameters of the α → β polymorphic transition have been derived from the calorimetric results.     

Preparation and characterization of Zn(0.9)Mg(0.1)TiO3via electrospinning

Hexagonal Zn(0.9)Mg(0.1)TiO(3) (ZMT) composite fibers were successfully prepared by combining sol-gel with an electrospinning and calcination technique. The crystalline phase and microstructures of Zn(0.9)Mg(0.1)TiO(3) fibers, calcined at various temperatures for 1 h, were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy and thermogravimetry differential thermal analysis (TG-DTA) techniques. The results showed that the crystalline phase, morphology and grain size of the ZMT fibers were influenced by the calcination temperature and the doped magnesium improved the stability of the ilmenite ZnTiO(3)-based ceramic. Fibrous, linked particles and separated hexagonal particles were obtained after being calcined at 500, 700 and 900 °C, respectively. The single phase Zn(0.9)Mg(0.1)TiO(3) was formed from 700 °C to 900 °C and the possible formation mechanism was proposed. The as-prepared samples exhibited low activities for Methylene blue (MB) photodegradation under visible-light irradiation.     

Polymorphism in copper pyrovanadate

Formation and stability temperatures were determined for the three polymorphs of copper pyrovanadate. The low-temperature β phase is formed at 500°C and is stable from room temperature to 610°C. The intermediate phase is stable within 610–705°C. The high-temperature γ phase is stable within 710–780°C. The rates of γ → α and α → β phase transitions upon cooling differ considerably. α-Cu₂V₂O₇ detected at room temperature upon cooling of a molten sample is metastable.     

Electrical conductivity and phase transitions of the solid electrolyte system (Cs1−yRby)Cu4Cl3(I2−xClx)

Results of electrical conductivity measurements, thermal analysis, and X-ray diffraction studies indicate the existence of four phases, between 295 K and the melting points, in the system (Cs_1?yRb_y)Cu₄Cl₃I₂. These phases are designated α, á β, γ in order of decreasing temperature. The α phase is isostructural with α-RbAg₄I₅; the á phase is also cubic and very likely belongs to space groupP2₁3, a subgroup ofP4₁32 andP4₃32 to which the α phase belongs. There is a high probability that the á → α transition is continuous. The á → α transition is not discernible in the conductivity measurements or thermal analysis; therefore the line of á-α transitions is presently unknown. The β phase transforms to the á and the γ phase transforms to the β phase wheny ≤ 0.36; the γ phase transforms to the α phase wheny ≥ 0.36. That is, there is a triple point aty = 0.36, T = 399K. The γ-β, β-α′, and γ-α transitions are all hysteretic and are therefore first order. The conductivities of the β phases are relatively low and the enthalpies of activation relatively high. The conductivity of the β phase decreases with increasingy. The β phase probably belongs to space groupR3, in which the Cu⁺ ions can be ordered. The α and á phases are the true solid electrolytes; the conductivities are high, >0.73 Ω^?1cm^?1 at 419 K, and the enthalpies of activation of motion of the Cu⁺ ions low, 0.11 eV.In the system CsCu₄Cl₃(I_2?xCl_x), 0 ≤ x ≤ 0.25, the Cl^? for I^? substitutions affect the transitions to only a small extent relative to the stoichiometric compound. The β phase occurs for allx and transforms to á.     

Thermal decomposition and cobalt species transformation of carbon nanotubes supported cobalt catalyst for Fischer-Tropsch synthesis

The effect of calcination condition on the cobalt species and Fischer-Tropsch synthesis (FTS) was studied. It was found that higher calcination temperature resulted in decreased FTS activities because CNTs were consumed by oxidation in air at temperature higher than 230°C. Cobalt species went through transformation from Co3O4 to metallic Co in Ar by autoreduction at temperature over 500°C. The autoreduction route might be Co3O4→CoO→Co or Co3O4→Co2C→Co. Reduction at temperature higher than 500°C also resulted in decreased FTS activities due to the methanation of CNTs in hydrogen.     

Landau theory description of observed isotropic to anisotropic phase transition in mixed clay gels

A characteristic new cooperative dehydration transition, in 1:1 Laponite-MMT cogel, was observed at T(c) ≈ 60 °C, a temperature at which the storage modulus (G(')) and depolarization ratio (D(p)) showed sharp increase, and the isotropic cogel turned into an anisotropic one. The dehydration dynamics could be described through power-law relations: G(') ～ (T(c)-T)(-γ) and D(p) ～ (T(c)-T)(-β) with γ ≈ β = 0.40 ± 0.05. The x-ray diffraction data revealed that the crystallite size decreased from 17 nm (at 20 °C) to 10 nm (at 80 °C) implying loss of free and inter-planar water. When this cogel was spontaneously cooled below T(c), it exhibited much larger storage modulii values which implied the existence of several metastable states in this system. This phase transition could be modeled through Landau theory, where the depolarization ratio was used as experimental order parameter (ψ). This parameter was found to scale with temperature, as ψ ～ (T(c)-T)(-α), with power-law exponent α = 0.40 ± 0.05; interestingly, we found α ≈ β ≈ γ.     

High-temperature phases of poly(p-xylylene)

The crystal structure of poly(p-xylylene), as polymerized, is the α form. This transforms irreversibly to the β from by annealing or drawing. To clarify the mechanism of this transition, structural changes of the α and β crystals were examined with a high-temperature stage in the electron microscope. Two high-temperature phases, β₁ and β₂, were found and their structures were analyzed. In these structures lattice distortions due to rotational and translational motions of chains are in troduced, especially in the β₂ form. The α → β transition is induced through such a disordered phase. The statistical arrangement of a molecule in the β-form unit cell results from freezing the disorder in the high-temperature phases.     

Synthesis, thermal and spectral characterization of nanosized Ni(x)Mg(1-x)Al2O4 powders as new ceramic pigments via combustion route using 3-methylpyrozole-5-one as fuel

New Ni(x)Mg(1-x)Al(2)O(4) nanosized in different composition (0.1≤x≤0.8) powders have been synthesized successively for first time by using low temperature combustion reaction (LTCR) of corresponding metal chlorides, carbonates and nitrates as salts with 3-methylpyrozole-5-one (3MP5O) as fuel at 300°C in open air furnace. Magnesium aluminate spinel (MgAl(2)O(4)) was used as crystalline host network for the synthesis of nickel-based nano ceramic pigments. The structure of prepared samples was characterized by using different techniques such as thermal analysis (TG-DTG/DTA), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). UV/Visible and Diffuse reflectance spectroscopy (DRS) using CIE-L*a*b* parameters methods have been used for color measurements. The obtained results reveal that Ni(x)Mg(1-x)Al(2)O(4) powder of samples is formed in the single crystalline and pure phase with average particle size of 6.35-33.11 nm in the temperature range 500-1200°C. The density, particle size, shape and color are determined for all prepared samples with different calcination time and temperature.     

Synthesis of the pentasaccharide repeating unit of the O-specific polysaccharide from salmonella strasbourg

The pentasaccharide α - Tyv - (1→3) - β - d - Man - (1→4) - α - l - Rha - (1→3) - d - Gal - (4←1) -α - d - Glc 1, the repeating unit of the O-specific polysaccharide chain of the lipopolysaccharide from S. Strasbourg, was obtained by glycosylation of benzyl - 2,6 - di - O - benzyl - 4 - O - (2,3,4 - tri - O - benzyl - 6 - O - benzoyl - α - d - glucopyranosyl) - β - d - galactopyranoside with 1,2 - methylorthoacetyl - 3 - O - acetyl - 4- O - [3 - O - (2,4 - di - O - acetyl - 3, 6 - dideoxy,- α - d - arabino - hexopyranosyl) - 2,4,6 - tri - O - acetyl - β - d - mannopyranosyl] - β - l - rhamnopyranose 3 followed by removal of protecting groups. The structure of the synthetic pentasaccharide was proved by methylation analysis and ¹³C NMR.     

Dynamical observation of structural transition of polymers using an X‐ray diffraction system with imaging plates. II. Crystalline transition of poly(butylene terephthalate)

Poly(butylene terephthalate) has two crystalline forms of α and β. The α form is more stable and is transformed into the β form by stretching. The α↔β transition stress was measured at various temperatures with the use of an X‐ray diffraction system with imaging plates, and the relationship between the transition stress and temperature was obtained. Further, using the X‐ray diffraction system, the drawing behavior of the nearly amorphous, undrawn polymer film was observed by taking up dynamically a series of X‐ray diffraction patterns while a film was being drawn. The α form never occurred during drawing at any temperature because the stress to draw the film exceeded the α→β transition stress. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 838–845, 2000     

Luminescence properties of Tb(3+)-doped CaMoO(4) nanoparticles: annealing effect, polar medium dispersible, polymer film and core-shell formation

Tb(3+)-doped CaMoO(4) (Tb(3+) = 1, 3, 5, 7, 10, 15 and 20 atom%) core and core-shell nanoparticles have been prepared by urea hydrolysis in ethylene glycol (EG) as capping agent as well as reaction medium at low temperature ～150 °C. As-prepared samples were annealed at 500 and 900 °C for 4 h to eliminate unwanted hydrocarbons and/or H(2)O present in the sample and to improve crystallinity. The synthesised nanophosphors show tetragonal phase structure. The crystallite size of as-prepared sample is found to be ～18 nm. The luminescence intensity of the (5)D(4) → (7)F(5) transition at 547 nm of Tb(3+) is much higher than that of the (5)D(4) → (7)F(6) transition at 492 nm. 900 °C annealed samples show the highest luminescence intensity. The intensity ratio R (I[(5)D(4) → (7)F(6)]/I[(5)D(4) → (7)F(5)]) lies between 0.3-0.6 for as-prepared, 500 and 900 °C annealed samples. The luminescence decay of (5)D(4) level under 355 nm excitation shows biexponential behaviour indicating availability of Tb(3+) ions on surface and core regions of particle; whereas, contribution of Mo-O charge transfer to lifetime is obtained under 250 nm excitation. The CIE coordinates of as-prepared, 500 and 900 °C annealed 5 atom% Tb(3+)-doped CaMoO(4) samples under 250 nm excitation are (0.28, 0.32), (0.22, 0.28) and (0.25, 0.52), respectively. The dispersed particles in polar medium and its polymer film show green light emission. The luminescence intensity is improved significantly after core-shell formation due to extent of decrease of non-radiative rates arising from surface dangling bonds and capping agent. Quantum yields of as-prepared samples of 1, 5 and 7 atom% Tb(3+)-doped CaMoO(4) samples are found to be 10, 3 and 2, respectively.     

Struktur und synthese von flavonol-triosiden aus rhamnus-arten

By synthesis and ¹³C-NMR spectroscopic investigations of rhamnocitrin-, rhamnazin- and rhamnetin - 3 - O - [O - α - l - rhamnopyranosyl - (1 → 4) - O - α - l - rhamnopyranosyl - (1 → 6)] β - d - galactopyranosides and of rhamnocitrin - 3 - O - [O - α - l - rhamnopyranosyl - (1 → 3) - O - α - l - rhamnopyranosyl - (1 → 6)] - β - d - galactopyranoside (rhamnocitrin - 3 - O - β - rhamnisoide) it was proved that all naturally occurring flavonoltriosides, so far isolated from different Rhamnus species, contain the sugar-moiety rhamninose. Thus it was shown that catharticin (rhamnocitrin - 3 - O - β - rhamninoside) is identical with alaternin and xanthorhamnin A (rhamnetin - 3 - O - β - rhamninoside) with xanthorhamnin B, whereas xanthorhamnin C is rhamnazin - 3- O - β - rhamninoside. From Rhamnus saxatilis JACQ., ssp. saxat. a new flavonol - acetyl - trioside was isolated and the structure by MS and ¹³C-NMR spectroscopic means elucidated to be the rhamnetin - 3 - O - [O - α - l - rhamnopyranosyl - (1 → 3) - O - (4 - O - acetyl - ) - α - l - rhamnopyranosyl - (1 → 6)] - β - d - galactopyranoside.     

Dielectric relaxation studies in poly(hexamethylenesebacate) (HMS), poly(2-methyl-2-ethyl propylenesebacate) (MEPS), poly(2,5-dimethylbutylene sebacate) (DBS), and block copolymers of HMS and MEPS

The α and β dielectric relaxations of poly(hexamethylenesebacate) (HMS), poly(2-methyl-2-ethyl propylenesebacate) (MEPS), poly(1,4- dimethylbutylene sebacate) (DBS) and block copolymers of HMS and MEPS have been studied. The α relaxation is amenable to a W.L.F. analysis and is associated with the glass transition of the polymers. This relaxation moves to higher temperatures with increasing HMS content in HMS/MEPS block copolymers. All the polymers studied exhibit psuedo-activation energies of ～32 kcal/mole at the glass transition. It is concluded that because the superposition principle is operative in the block copolymers, the glass transition must be very similar in both polymers and morphology and degree of crystallinity do not greatly affect this transition. The β relaxation which has been associated with segmental relaxation of polymethylene segments in polymers is also shown to be a function of HMS/MEPS block copolymer composition and chemical structure. This relaxation takes place at lower temperatures with increased HMS content in the blocks and also shifts to lower temperatures with side chain substitution adjacent to the carbonyl group in the polymer. It is concluded that the β relaxation takes place in the amorphous and crystalline regions of the polymer.     

Synthesis and Structure of Bismuth(III)-Containing Noncentrosymmetric Phosphates, Cs(3)KBi(2)M(4)(PO(4))(6)Cl (M = Mn, Fe). Monoclinic (Cc) and Tetragonal (P4(3)) Polymorphs Templated by Chlorine-Centered Cl(Bi(2)Cs) Acentric Units

Single crystals of three new noncentrosymmetric (NCS) phosphates, α (1) and β (2) forms of Cs(3)KBi(2)Mn(4)(PO(4))(6)Cl and α-Cs(3)KBi(2)Fe(4)(PO(4))(6)Cl (3), were grown in a reactive CsCl/KCl molten-salt media. Their structures were determined by single-crystal X-ray diffraction methods showing that the α form crystallizes in the space group Cc (No. 9), which is in one of the 10 NCS polar crystal classes, m (2/m) while the β form crystallizes in P4(3) (No. 78) of another polar class, 4 (4/m). The unit cell parameters of the α form can be approximately correlated with that of the β form via the 3 × 3 orientation matrix [0.5, 0.5, 0; -0.5, 0.5, 0; 0, 0, 2 sin β]. The structures of these otherwise complicated phosphates exhibit two types of channels with circular and elliptical windows where the Cl-centered Cl(Bi(2)Cs) acentric unit is located. The neighboring acentric units are arranged in a parallel fashion in the α form, resulting in the monoclinic (Cc) lattice, but "antiparallel" in the β form, thus giving the tetragonal (P4(3)) unit cell. 1-3 feature the compatible M-O-P unit that contains four crystallographically independent MO(x) (x = 4, 5) polyhedra, which are connected to the Cl(Bi(2)Cs) acentric unit through one short and one long M(II)···Cl bond. The compositions of 1 and 2 consist of three Mn(2+) (d(5)) and one Mn(3+) (d(4)) per formula unit and that of 3 has three Fe(2+) (d(6)) and one Fe(3+) (d(5)). Bond valence sums reveal that, in the α phase, the trivalent site adopts distorted tetrahedral M(1)(3+)O(4) coordination and, in the β phase, distorted trigonal-bipyramidal M(4)(3+)O(5). Thus far, the iron phase has only been isolated in the α form presumably because of little extra stabilization energy gain if the Fe(2+) d(6) ion were to occupy the M(1)O(4) site. The possible origins pertaining to the structural differences in the α and β forms are discussed.     

Magnetic properties and magnetic structures of synthetic natrochalcites, NaM(II)2(D3O2)(MoO4)2, M = Co or Ni

The magnetic properties and magnetic structures from neutron diffraction of two synthetic natrochalcites, NaM(II)2(H3O2)(MoO4)2, M = Co (1Co) or Ni (2Ni), are reported. They are isostructural (monoclinic C2/m) and consist of chains of edge-shared MO6 octahedra connected by mu-O from H3O2(-) and MoO4(2-). These chains form a three-dimensional network with O-H-O, O-Mo-O, and O-Na-O bridging 4, 3, and 4 metal ions, respectively. Both compounds behave as canted antiferromagnets but differ in their behaviors, 1Co showing a broad maximum (28 K) above the Neel transition (21 K) and the canting taking place at 13 K, some 8 K below T(N), while for 2Ni the canting takes place at T(N) (28 K). Analyses of the neutron powder diffraction data shed some light on the geometry of D3O2(-) and suggest antiferromagnetism with a propagation vector k = (0,0,0) with the moments within each chain being parallel but antiparallel to those in neighboring chains. The difference between 1Co and 2Ni is in the orientation of the moments; they are parallel to the chain axis (b-axis) for 1Co and perpendicular to it for 2Ni with a major component along the c-axis and a small one along the a-axis. The heat capacity data peak at 20.9(3) K (1Co) and 25.1(1) K (2Ni). The derived magnetic entropies, following correction of the lattice contribution using the measured data for the nonmagnetic Zn analogue, suggest S = 1/2 for 1Co but is lower than that expected for 2Ni (S = 1). In both cases, only ca. 60% of the entropy is found below the magnetic ordering temperature, suggesting considerable short-range correlations at higher temperatures. While the temperature at which the magnetic diffraction becomes observable coincides with that of at the peak in heat capacity, it is lower than T(N) observed by magnetization measurements in both cases, and there is evidence of short-range ordering in a narrow range of temperature (T(N) +/- 5 K).     

A new partially deprotonated mixed-valence manganese(II,III) hydroxide-arsenate with electronic conductivity: magnetic properties of high- and room-temperature sarkinite

A new three-dimensional hydroxide-arsenate compound called compound 2 has been synthesized by heating (in air) of the sarkinite phase, Mn(2)(OH)AsO(4) (compound 1), with temperature and time control. The crystal structure of this high-temperature compound has been solved by Patterson-function direct methods. A relevant feature of this new material is that it is actually the first member of the adamite-type family with mixed-valence manganese(II,III) and electronic conductivity. Crystal data: a = 6.7367(5) ?, b = 7.5220(6) ?, c = 9.8117(6) ?, α = 92.410(4)°, β = 109.840(4)°, γ = 115.946(4)°, P1?. The unit cell content derived from Rietveld refinement is Mn(8)(O(4)H(x))(AsO(4))(4). Its framework, projected along [111], is characterized by rings of eight Mn atoms with the OH(-)/O(2-) inside the rings. These rings form an almost perfect hexagonal arrangement with the AsO(4) groups placed in between. Bond-valence analysis indicates both partial deprotonation (x ? 3) and the presence of Mn in two different oxidation states (II and III), which is consistent with the electronic conductivity above 300 °C from electrochemical measurements. The electron paramagnetic resonance spectra of compound 1 and of its high-temperature form compound 2 show the presence of antiferromagnetic interactions with stronger magnetic coupling for the high-temperature phase. Magnetization measurements of room-temperature compound 1 show a complex magnetic behavior, with a three-dimensional antiferromagnetic ordering and magnetic anomalies at low temperatures, whereas for compound 2, an ordered state is not reached. Magnetostructural correlations indicate that superexchange interactions via oxygen are present in both compounds. The values of the magnetic exchange pathways [Mn-O-Mn] are characteristic of antiferromagnetic couplings. Notwithstanding, the existence of competition between different magnetic interactions through superexchange pathways can cause the complex magnetic behavior of compound 1. The loss of three-dimensional magnetic ordering by heating of compound 1 could well be based on the presence of Mn(3+) ions (d(4)) in compound 2.     

Synthesis, characterization, and structure-property relationships in two new polar oxides: Zn2(MoO4)(SeO3) and Zn2(MoO4)(TeO3)

Two new noncentrosymmetric (NCS) polar oxide materials, Zn(2)(MoO(4))(AO(3)) (A = Se(4+) or Te(4+)), have been synthesized by hydrothermal and solid-state techniques. Their crystal structures have been determined, and characterization of their functional properties (second-harmonic generation, piezoelectricity, and polarization) has been performed. The isostructural materials exhibit a three-dimensional network consisting of ZnO(4), ZnO(6), MoO(4), and AO(3) polyhedra that share edges and corners. Powder second-harmonic generation (SHG) measurements using 1064 nm radiation indicate the materials exhibit moderate SHG efficiencies of 100 × and 80 × α-SiO(2) for Zn(2)(MoO(4))(SeO(3)) and Zn(2)(MoO(4))(TeO(3)), respectively. Particle size vs SHG efficiency measurements indicate the materials are type 1 non-phase-matchable. Converse piezoelectric measurements resulted in d(33) values of ～14 and ～30 pm/V for Zn(2)(MoO(4))(SeO(3)) and Zn(2)(MoO(4))(TeO(3)), respectively, whereas pyroelectric measurements revealed coefficients of -0.31 and -0.64 μC/m(2) K at 55 °C for Zn(2)(MoO(4))(SeO(3)) and Zn(2)(MoO(4))(TeO(3)), respectively. Frequency-dependent polarization measurements confirmed that all of the materials are nonferroelectric; that is, the macroscopic polarization is not reversible, or "switchable". Infrared, UV-vis, thermogravimetric, and differential thermal analysis measurements were also performed. First-principles density functional theory (DFT) electronic structure calculations were also done. Crystal data: Zn(2)(MoO(4))(SeO(3)), monoclinic, space group P2(1) (No. 4), a = 5.1809(4) ?, b = 8.3238(7) ?, c = 7.1541(6) ?, β = 99.413(1)°, V = 305.2(1) ?(3), Z = 2; Zn(2)(MoO(4))(TeO(3)), monoclinic, space group P2(1) (No. 4), a = 5.178(4) ?, b = 8.409(6) ?, c = 7.241(5) ?, β = 99.351(8)°, V = 311.1(4) ?(3), Z = 2.     

Synthesis of silicon doped SrMO3 (M = Mn, Co): stabilization of the cubic perovskite and enhancement in conductivity

In this paper we report the successful incorporation of silicon into SrMO(3) (M = Co, Mn) leading to a structural change from a hexagonal to a cubic perovskite. For M = Co, the cubic phase was observed for low doping levels (3%), and these doped phases showed very high conductivities (up to ≈350 Scm(-1) at room temperature). However, annealing studies at intermediate temperatures (700-800 °C), indicated that the cubic phase was metastable with a gradual transformation to a hexagonal cell on annealing. Further work showed that co-doping with Fe resulted in improved stability of the cubic phase; a composition SrCo(0.85)Fe(0.1)Si(0.05)O(3-y) displayed good stability at intermediate temperatures and a high conductivity (≈150 Scm(-1) at room temperature). For M = Mn, the work showed that higher substitution levels were required to form the cubic perovskite (≈15% Si doping), although in these cases the phases were shown to be stable to annealing at intermediate temperatures. Conductivity measurements again showed an enhancement in the conductivity on Si doping, although the conductivities were lower (≈0.3-14 Scm(-1) in the range 20-800 °C) than the cobalt containing systems. The conductivities of both systems suggest potential for use as cathode materials in solid oxide fuel cells.     

Über Reaktionen oxygenierter Kobalt(II)-Chelate. II. Konfigurationsisomere Oxygenierungsprodukte von Tetraäthylenpentaminkobalt(II)

On oxygenation of alcoholic solutions of tetraethylenepentamine cobalt(II) two isomeric forms of [(tetren)CoO₂Co(tetren)]⁴⁺ are obtained in which the configuration of the pentadentate ligand is either α or β. The binuclear complex can be crystallized as thiocyanate or as perchlorate. Oxygenation at 35° produces the pure α isomer. At lower temperature a mixture of α and β is obtained. The isomers differ slightly in their absorption spectra and their reactivity. The ligand configuration has been elucidated by transforming the perchlorates into the [ZnCl₄]^2? salts of the corresponding mononuclear chelates [Co(tetren)Cl]²⁺. The latter have also been prepared starting from a compound of known configuration according to the literature. The IR. spectra of the α and β forms differ characteristically in the NH stretch bands.