European Journal of Solid State and Inorganic Chemistry最新文献

The location of Eu³⁺ in α-cordierite, synthesized by a sol-gel route, was investigated by using both site-selective spectroscopy and time-resolved spectroscopy. ⁷F₀ → ⁵D_1,2 excitation and ⁵D₀ → ⁷F_0,1,2 emission spectra were performed at 77 K. The Eu³⁺ ions are distributed in two families : the A family in the structure channels and the B family at (4c) position of D_2h¹⁶ in substitution for Mg²⁺ Four B sub-families were characterized and understood as a difference at the second neighbours, i.e., the four possible occupations of the surrounding tetrahedra by Al and Si. The A family was characterized by anomalous spectra: strong ⁵D₀ → ⁷F₀ transition, high position of the ⁵D₀, ⁵D₁ and ⁵D₂ levels and very large ⁷F_1,2 splittings. By comparison with Eu-doped apatites, in which similar features occur, a predominant Eu-O bonding of covalent character with one of the oxygen ions bordering the channel was assumed. When the annealing temperature increases, Eu³⁺ ions migrate from the channel to the (4c) position.

Thermal Residual Stresses (TRS) induced by cooling down from elaboration process in SiC/ Ti-15-3 composite are evaluated using several models (present in part I). Influence of thermomechanical properties is investigated. It is shown that a small uncertainly on coefficient of thermal expansion has a huge influence on TRS. It is also highlight that the analytical model proposed is a suitable model to obtain quickly information about TRS (rather than the finite element analysis which is a little more accurate but longer too).

Then evolution (relaxation) of the TRS during a fatigue test are investigated. Results show that the TRS decrease rapidly during the first cycles and then become almost constant at about one third of their initial values.

A chain-like zincophosphate [Zn₈(HPO₄)₈(H₂PO₄)₈]•[(C₂H₈N)₈]•4H₂O was obtained at room temperature from a ZnO/P₂O₅/dimethylamine/H₂O mixture. The crystal structure was determined by single crystal X-ray diffraction. The symmetry is monoclinic a=1.26450(7)nm, b=1.08477(5)nm, c=1.46311(4)nm, β=98.793(5)°, space group Cc. The structure consists of chains of zinc-corner-sharing Zn₂P₂O₄ four rings. The negative charge of the chains is compensated by the protonated dimethylamine. The characterization by ³¹P solid state nmr spectroscopy is also reported.

A new gallophosphate was synthesized in aqueous medium using the macrocycle 1,4,8,11-tetraazacyclotetradecane as organic species. The structure was determined by single crystal X-ray diffraction. The symmetry is monoclinic, space group C2/c, a=0.8842(3)nm, b=1.7781(2)nm, c=1.5805(3)nm, β= 92.05(3)°. The structure consists of gallophosphate chains of gallium-corner-sharing Ga₂P₂O₄ four-rings. Each chain is connected to the others via a gallium-organic complex leading to a three dimensional framework. This new gallophosphate shows low thermal stability, a complete amorphization being observed after calcination at 350°C. The results of ¹³C and ³¹P solid state nmr spectroscopy are in agreement with the structure analysis.

Different models for the calculation of residual stresses induced by cooling down from elaboration process in SiC/Ti-15-3 composite were presented. First of all, an analytical model (derived from those of Eshelby and of Mikata and Taya) already used for ceramic matrix composites is explained. It is a suitable method for elementary composites but we present an extension of this model to real (1D) composites. Then, we also briefly present the finite model using MARC anc MENTAT softwares. Finaly, an analytical model to predict the evolution of TRS during a fatigue test is detailed. The part II of the paper will present the results obtained using all these differents models.

α-Ba₂ZrF₈ is prepared as systematically twinned crystals by hydrothermal synthesis (200°C) or as fine powders either on a sand bath (60°C) (aqueous HF medium) or by solid state reaction at 450°C. Synchrotron radiation was used because of ambiguities in indexations from conventional X-ray (pseudo-hexagonal symmetry). The structure was determined ab initio from synchrotron powder data. Neutron data were used for improving accuracy because some degree of non-stoichiometry was suspected. The cell is orthorhombic, space group Prima, Z = 4, with a = 9.7401(1) Å, b = 5.6147(1) Å and c = 11.8871(1) Å (synchrotron data, 25°C). The final neutron Rietveld refinement led to R_P = 8.4 % and R_B = 3.5 % for the stoichiometric Ba₂ZrF₈ formulation (sand bath sample). The structure is built up from [ZrF₈] bicapped trigonal prisms isolated in a kinked fluorite matrix. The isostructural Pb₂ZrF₈ compound prepared in solution is also examined. An unexpected relationship with NaBaZrF₇ is discussed.

Crystals of sodium doped lanthanum orthomanganites were grown for the first time in sodium chloride flux at 900°C. 0.5 to 0.1mm size crystals were isolated. Composition of the oxide, La_0.82Na_0.13MnO_2.93 was arrived at by chemical analysis of the elements present. Single crystal X-ray structural study showed that the lanthanum as well as oxygen site deficient orthomanganites crystallize in R3¯ space group unlike many divalent cation doped lanthanum orthomanganites which crystallize in R3¯.

Dicopper diacetylide Cu-C≡C-C≡C-Cu, prepared from butadiyne has been studied by FT-IR spectroscopy in comparison to dicopper acetylide Cu-C≡C-Cu. Upon ageing by exposure to air at room temperature, Cu-C≡C-Cu has been transformed into Cu-C≡C-C≡C-Cu as demonstrated by FT-IR spectroscopy and this compound is further transformed on standing in air. A special kind of solid state oxidative coupling reaction occurs so that polyynes chains are formed in these aged solids. It is shown that the FT-IR spectrum of copper acetylide prepared from ammonia solutions of Cu⁺ and Cu²⁺ ions is comparable to that of air oxidized Cu-C≡C-Cu (and Cu-C≡C-C≡C-Cu) prepared exclusively from Cu⁺ ions in presence of a reducing agent demonstrating that Cu²⁺ ions display the same oxidizing effect as oxygen causing coupling reactions in solution and producing Cu-C≡C-C≡C-Cu.

Cu-C≡C-Cu oxidized at 60–70°C with CuCl₂ produces a product which could be formulated as Cu(C≡C)₂₀Cu; FT-IR absorption at 1950 cm⁻¹ could suggest the presence of cumulenic carbon chain although acetylenic carbon chains cannot be excluded completely.

α-NaCaAlF₆ is prepared by solid state reaction as poor quality crystals. The structure is determined ab initio from conventional X-ray powder data. The cell is monoclinic, space group P2₁/c, Z = 8, with a = 8.7423(3) Å, b = 5.1927(2) Å, c = 20.3514(9) Å and β = 91.499(2)°. The final Rietveld refinement leads to R_P = 10.6% and R_B = 5.2 %. The structure is built up from isolated AlF₆ octahedra, interconnected by CaF₇ polyhedra sandwiched between layers of NaF₈ and NaF₇ polyhedra extending in the be plane.

Hydrolysis of dicopper diacetylide Cu-C≡C-C≡C-Cu in HCl solution yields diacetylene as major product together with a mixture of polyynes and minor amounts of carbonaceous matter. After I month ageing the main hydrolysis product from dicopper diacetylide is insoluble carbonaceous matter (23.47% by weight) together with diacetylene and its superior homologues (polyynes formed from solid state oxidative coupling reaction) which have been qualitatively and quantitatively identified by electronic spectroscopy. Similar behaviour and results are observed on dicoppper acetylide Cu-C≡C-Cu. In the carbonaceous insoluble matter recovered after hydrolysis, the presence of carbyne was detected by FT-IR spectroscopy.

Dicopper acetylide Cu-C≡C-C≡C-Cu and dicopper acetylide, irrespective for the degree of oxidation reached in air, undergo a controlled thermal decomposition by heating under reduced pressure yielding in few seconds carbyne and copper(I) oxide, both identified by FT-IR spectroscopy.