European Journal of Solid State and Inorganic Chemistry最新文献

After a short survey of what is the present state of the cyclophosphates associated with the organic molecule NH₂(CH₂)₄NH₂, we report chemical preparation and crystal structure for a new example of such compounds. [NH₃(CH₂)₄NH₃]₂P₄O₁₂.2H₂O is monoclinic (S.G. : P2₁/n), with Z = 2 and the following unit-cell parameters : a = 7.6728(8) Å, b = 18.962(3) Å, c = 7.9789(9) Å β = 111.751(9)°. Bidimensional layer arrangement of P₄O₁₂ rings connected to the water molecules thanks to weak H-bonds run parallel to the ab plane. The organic groupements located between these inorganic planes perform the three-dimensional cohesion by NH····O hydrogen bonds.

Preparation, characterization by X-ray diffraction, IR absorption, DTA-GTA analysis and ab-initio crystal structure determination are reported for a new lithium cyclohexaphosphate hydrate Li₆P₆O₁₈·3H₂O. It crystallizes in a trigonal (rhomboedral) cell (space group R 3¯m No 166, Z = 6) with a = 15.7442(2) Å, c = 12.5486(2) Å. X-ray powder diffraction pattern data was refined by Rietveld profile technique and lead to R_Bragg = 0.09. The crystal structure of Li₆P₆O₁₈·3H₂O is built up from [P₆O₁₈]^6- ring anions, having the 3m symmetry, alternating along the 3¯ axis with rings made of six LiO₄ tetrahedra and six LiO₅ pseudo square pyramids sharing common edges.

In the present work it has been demonstrated, by measurements of their density and air oxidation resistance, that different sorts of carbon fibres grown from a gaseous stage, vapour grown carbon fibres (VGCF), present a duplex structure. By means of these two experimental techniques, structural differences between both constituent phases of this kind of fibres have been determined. It has been proved that the catalytic phase or nucleus presents higher level of crystalline perfection than the pyrolytic or cortical phase. This is corroborated by the fact that thin VGCF show better mechanical properties than thick fibres.

In this way, it has been possible to determine the mean nucleus diameter of a batch of VGCF, and to established a mathematical expression, of the rule of mixtures type, for their density.

We investigated the feasability of elaboration by the pyrosol process, on various substrates, of PZT (52/48) ferroelectric phases in thin film configuration. Changes in the deposition process, such as the introduction of multilayer techniques, as well as exand in-situ post-depositional annealing treatments, were applied in order to evaluate their impact on the composition, surface morphology and crystallinity. Under certain conditions, the perovskite phase was found to comprise up to 80% of the crystalline material in films elaborated with an in-situ annealing treatment. The primary competing phase in impure deposits was lead oxide.

The bis(cyclopropylammonium)dihydrogenodiphosphate monohydrate is a new diphosphate associated with the organic molecule C₃H₅NH₂. We report the chemical preparation and the crystal structure of this organic cation diphosphate. (C₃H₅NH₃)₂H₂P₂O₇.H₂O is orthorhombic (S.G. : P2₁2₁2₁), with Z = 4 and the following unit-cell parameters : a = 4.828(1) Å, b = 11.011(1) Å, c = 25.645(2) Å. The P₂O₇ groups and H₂O water molecules form a succession of bidimensional layers perpendicular to the c axis. The organic cations ensure the three-dimensional cohesion by NH-O hydrogen bonds.

Quenching of Na₂SO₄ - CaSO₄ melts down to room temperature results in different forms of metastable solid solutions dependent on the CaSO₄ content. The transformation of these solid solutions into stable phases were investigated after various times and temperatures by X-ray powder diffraction and thermal analyses. An equilibrium phase diagram is derived, which is in accordance with all experimental facts.

Intense ultrasonic treatment caused CS₂ sonolysis with formation of several products like sulfur, carbon subsulfide C₃S₂, and a black insoluble sonopolymer. The sonolysis products was analyzed by electronic spectroscopy and liquid chromatography (HPLC). The black insoluble sonopolymer was studied in detail by FT-IR spectroscopy and was found to be chemically similar to the CS₂ photopolymer and to the piezopolymer. FT-IR shows that the sonopolymer prepared at room temperature is the ladder carbon subsulfide polymer (C₃S₂)_x, having the linear polymer -[S-(C=S)-S-(C=S)-]_x-, as minor component. When sonication is conducted at −78°C, FT-IR spectrum shows that the sonopolymer in addition to carbon subsulfide polymer (C₃S₂)_x contains the carbon disulfide dimer (C₂S₄) previously detected in the piezopolymer.

A discussion of the mechanism of sonolysis of carbon disulfide shows that the “hot spot” theory involving high pressure and temperature generated by cavitational bubbles can explain the results at −78°C, but not at room temperature. To explain sonolysis at 0°C or higher temperature, electric breakdown inside cavitational bubbles should be considered.

The aerial oxidation of aqueous suspensions of ferrous hydroxide precipitated from ferrous oxalate and caustic soda can lead to an iron (II)-iron (III) hydroxy-oxalate of the pyroaurite group, a GR(C₂O₄^2-) Green Rust. As other GR compounds, it is unstable with respect to the action of oxygen and oxidises later on. Its chemical composition was determined to be [Fe^II₆ Fe^III₂(OH)₁₆]²⁺[C₂O₄^2- · nH₂O], with n more likely equal to 3 on the basis of structural considerations. The composition does not vary and the Fe (II) / Fe (III) ratio in the compound is measured by means of transmission Mössbauer spectroscopy at 78 K and 20 K in the range from 2.8 to 3.2 for various samples at various stages of the reaction. GR(C₂O₄^2-) is paramagnetic at both temperatures and is unambiguously distinguished from ferrous hydroxide, the initial reactant, and magnetite, the main final product, which are magnetically ordered at 20 K. The spectrum of the GR compound is composed of three quadrupole doublets, one due to the Fe(III) cations characterised by a small quadrupole splitting ΔE_Q of 0.40 mm s⁻¹, and two due to the Fe(II) cations, characterised by larger ΔE_Q values of about 2.55 and 2.85 mm s⁻¹. Finally, from the observed equilibrium conditions between ferrous hydroxide and GR(C₂O₄^2-), the standard free enthalpy of formation of GR(C₂O₄^2-) was computed to be : ΔG°_f[Fe^II₆ Fe^III₂ (OH)₁₆]²⁺[C₂O₄^2- · 3H₂O] = −5383 ± 3 kJ mol⁻¹.