Contribution de la spectrometrie mössbauer et de la spectrometrie d'absorption X A l'etude de la non-stoechiometrie de CuFe2O4

The effects of oxygen loss on the crystallographic and magnetic properties of CuFe₂O₄, ferrite have been studied by high-temperature x-ray diffraction, X-ray absorption spectrometry and Mössbauer spectrometry.In the heat-treatment under nitrogen, formation of a ferrimagnetic phase is observed with an increased content of Fe²⁺ and precipitation of CuFeO₂. Quenching after sintering leads to a mixture containing CuO and a spinel ferrimagnetic phase in which the oxygen deficiency involves the formation of Cu⁺.     

Contribution a l'etude de la conductivite ionique de l'orthophosphate Na3PO4

The present work is concerned with the ionic conductivity of pure trisodium orthophosphate Na₃PO₄, devoid of any trace of hydroxide NaOH. At the allotropic transition (330°C), we observe a jump of the ionic conductivity and a slight decrease in the activation energy (ΔE = 0,70 ± 0,02 eV for the quadratic variety and ΔE = 0,60 ± 0,04 eV for cubic γ-Na₃PO₄). Na₃PO₄ can be considered to be an electrolytic solid with medium conductivity ($\text{σ = 1.10}{}^{\mathrm{?4}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ at 370°C).     

Synthese et etude de verres fluores dans les systemes LnF3BaF2MnF2

New heavy metal fluoride glasses based on MnF₂ and rare-earth fluorides LnF₃ are reported. Vitreous materials have been obtained by quenching for Ln = Dy → Lu + Y; the limits of the glassy domain and the typical temperatures Tg, Tc, Tf are given. Optical measurements indicate that the I.R. absorption edge is situated in the 9–10 μm region.     

Nouveaux verres fluores transmetteurs dans l'infrarouge dans les systemes LnF3BaF2ZnF2

A new family of fluoride glasses have been isolated in the ternary systems LnF₃BaF₂ZnF₂ with Ln = rare earth and yttrium. The melt must be quenched to reduce the crystallization. These glasses have a good I.R. transmission: the absorption edge is in the 9 μ region.     

Synthese et etude structurale de l'oxyde double Dy5Re2O12

The unit cell of Dy₅Re₂O₁₂ is monoclinic, space group P2_l/m, with $\text{a}\text{= 12.425(8),}\text{b}\text{= 7.511(5),}\text{c}\text{= 5.653(5)}\text{A}\text{?}\text{, γ = 107.8(2)°,}\text{Z}\text{= 2}$.The crystal structure has been determined from single crystal diffractometer data. However, the presence of a polysynthetic twinning prevents a correct refinement.This structure is built from infinite chains of octaedra ReO₆ along c axis which are bridged along b axis by isolated octaedra DyO₆. These two types of octaedra from sheets along (100) between them are located the other Dy atoms which assume the cohesion of this tridimensionnal network.     

Étude en impulsion de l'injection et de la conduction dans les structures Si-SiO2-Al

We have studied the injection mechanisms at the Si-SiO₂ interface and the conduction in Si-SiO₂-Al devices. The use of a pulsed voltage makes it possible to apply fields of the order of 10⁷ V/cm to the thin oxide layer. The experimental I(V) characteristics prove the existence of the following mechanisms:-at weak fields (ε<3.5 x 10⁶ V/cm), Schottky injection of electrons at the temperature of the thermal lattice vibrations;-for 3.5 x 10⁶ V/cm<ε<8 x 10⁶ V/cm, injection of hot electrons (T_m? 6500°K) produced by an avalanche effect;-for ε>8 x 10⁶ V/cm, tunnel injection of electrons of an effective mass m? 0.4m₀.     

Utilisation de la deflection photothermique pour l'etude de l'effet du chlore sur l'absorption par les etats de la bande interdite dans a-SiHCl

Chlorinated and hydrogenated amorphous silicon (a-SiHCl) have been prepared by glow-discharge of a gas mixture (SiCl₄+H₂). Optical absorption and photothermal deflection spectroscopy have been made on samples with different chlorine contents. Due to its higher sensitivity, the photothermal deflection spectroscopy shows a decrease of the gap states absorption at low energies when the chlorine content is increased.     

Distribution du fluor et de l'oxygene dans l'oxyfluorotantalate de potassium K2Ta4O9F4

The crystal structure of potassium tantalum oxide fluoride K₂Ta₄O₉F₄ has been previously determined by X ray-diffraction, but this technique is unable to distinguish in the lattice between oxygen and fluorine atoms. From NMR measurements on ¹⁹F it is possible by a Van Vleck second moment approach to locate the F^? ions at the corners of the octahedra, forming infinite Ta-F-Ta … chains along the $\text{c}$ axis.     

Application de l'etude matricielle de la transformation de burgers a la precipitation des composes NiMo dans les aciers maraging a 18% Ni

This paper concerns a geometrical analysis by coincidence lattice method of aging processes in maraging steels. It is shown an equal formation probability for NiMo and Ni₃Mo precipitates in this martensitic matrix.     

Conductivite ionique de l'argent dans le compose Ag14Sb12O36F2 etude comparative avec la phase pyrochlore AgSbO3

The compound Ag₁₄Sb₁₂O₃₆F₂, with a desordered KSbO₃ cubic structure, is obtained by an ion exchange method. The conductivity of the silver ions in both Ag₁₄Sb₁₂O₃₆F₂ and AgSbO₃ pyrochlore compounds is investigated by measurement of complex impedance. The e.m.f. measurement and curves i vs. E show that the conduction is essentially assumed by Ag⁺ ions. This study confirms that the cubic KSbO₃ framework structures are good candidates for ionic conductors.     

Presence de l'eau dans V2O5 non cristallin

Non cristalline pentoxide V₂O₅ obtained from molten V₂O₅ using quenching method contains a few amount of water. Thermogravimetry, thermal analysis, mass spectrometer, aqueous dissolution demonstrate that it exists a relation between non cristalline structure and water bond. At 190°C, the oxide crystallises at the same time that the water is eliminated.     

Contribution a l'etude structurale des phases V1-xCrxO2

The authors have determined the phase diagram of the system V_1?xCr_xO₂ (0 ? x ? 0.15) by magnetic susceptibility, D. T. A. and X-ray diffraction measurements. At small chromium concentrations the existence of the intermediate phases M₂ and M₃, between M₁ and the rutile phase, has been confirmed. But it has been found that M₃ has actually a triclinic symmetry without destruction of the V-V pairs already existing in M₁. At higher concentrations (x > 0.07) there appears a monoclinic M₄ phase in which the V - V pairs are all destroyed.     

Contribution a l'etude des proprietes magnetiques du dichlorure de vanadium VCl2

The magnetic properties of VCl₂ have been interpreted on the basis of a G.S. Rushbrooke et P.J. Wood model for Heisenberg bidimensional interactions. The calculation of the exchange integral leads to a value of $\text{J}\text{k}{}_{\mathrm{b}}$ close to ? 22,5 K. The strong antiferromagnetic intraplanar V – V interactions seem to result from direct t_2g - t_2g coupling.     

Synthese et etude des proprietes spectrales de monocristaux de vanadate a structure grenat Ca2NaMg2V3O12 active par l'europium trivalent

Single crystals of garnet-type vanadates Ca_2?2xNa_1+xEu_xMg₂V₃O₁₂ have been obtained by the flux and Czochralski methods. Spectroscopic studies of Eu³⁺ ion in these single crystals confirm the precedent results obtained on powdered samples especially the lowering of the D₂ point symmetry of the dodecahedral site.     

Etude du comportement de l'antimoine v et du strontium dans les oxydes a structure en cages du type A3M8O21

New compounds Ba₃(Sb₄Ti₄)O₂₁ and Ba_3?xSr_x(M₄Ti₄)O₂₁ (M = Nb, Ta, Sb) isostructural with the niobates A₃(Nb_8?xM_x)O₂₁ previously described, have been synthesized. The influence of the antimony and strontium ions on the stability of the A₃M₈O₂₁ structure has been discussed in terms of electrostatic repulsion forces, polarization and covalency. Atomic positions, determined from powder diffraction patterns, are given for Ba₃(Sb₄Ti₄)O₂ and Sr₃(M₄Ti₄)O₂₁ (M = Nb, Ta).     

Variation thermique de la susceptibilite magnetique et de l'aimantation du ferrite bicalcique Ca2Fe2O5

An investigation of the magnetic susceptibility and the magnetization vs temperature has been carried out for Ca₂Fe₂O₅. The weak ferromagnetism behaviour of this compound was confirmed. The value of the ferromagnetic component was determined; an estimate of the various magnetic couplings was given and the importance of the thermal variation of the molecular field at high temperature pointed out.     

La liaison metal — metal dans les clusters M12O36: II — Preparation et etude structurale de la phase La3Ru3O11

La₃Ru₃O₁₁ was prepared either by oxidation of mixtures of $\text{3}\text{2}\text{La}{}_2\text{O}{}_3$: 3 Ru with KClO₃ at 900°C or by the oxidation of LaRuO₃ at 920°C with KClO₃, both in a gold boat introduced in a sealed silica tube. The crystal structure of this compound ($\text{a}\text{= 9.466(2)}\text{A}\text{?}\text{, S.G. Pn}\text{3,}\text{Z}\text{=4}$) has been solved by Fourier and least-squares methods to R = 0.022 (R_W = 0.031). As for the previously described Bi₃Ru₃O₁₁ and La₄Ru₆O₁₉, it contains ruthenium in formal oxidation state of 4.33; however, there is no longer metal - metal interaction, owing to the greater Ru - Ru distance (3.00 Å) and the closer approach of bridging oxygen (2.47 Å) within the dimeric unit Ru₂O₁₀. Therefore, this interaction is not a prerequisite for the formation and stability of the three-dimensional network Ru₁₂O₃₆.     

Intercalation d'ions metallicinium dans les gels de V2O5

Cobalticinium and ferricinium cations have been intercalated at room temperature into the lamellar structure of V₂O₅ gels. In both cases an almost constant basal d-spacing is observed, about 13.2 Å whatever the counterion used. The basic V₂O₅ ribbon structure is not modified upon intercalation, but noticeable improvement of the order along the ribbon packing direction is obtained, especially with Co(C₅H₅)⁺₂. The 4.4 Å increase in the basal d-spacing and its high temperature evolution allow to deduce that cyclopentadienyl rings interpenetrate the V₂O₅ ribbons presumably in the usual perpendicular position. Water is involved in the intercalation mechanism which is likely of the exchange type rather than of the redox type. Intercalate formula is approximately V₂O₅, 0.4 Fe(C₅H₅)₂, x H₂O (with x < 0.5). The materials, especially the Co(C₅H₅)⁺₂ intercalate, are still stable beyond 200°C. Such a high thermal stability is quite remarkable.     

Nature de la fluorescence de l'europium divalent dans les fluorures

The levels of the ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ (4f⁷) and 4f⁶5d¹ states of europium (+II) have been determined from fluorescence spectra in a series of fluorides M_xB_yF_z (M = alkaline-earth element, B = Li, Be, Mg, Y, Si). As in BaY₂F₈, SrSiF₆ and BaSiF₆, the ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ level lies even at room temperature far below the 4f⁶5d¹ band, only the f → f emission is observed. The influence of the choice of the alkaline-earth and the B cations and of the coordination of europium on the relative positions of the energy levels is discussed.     

Proprietes magnetiques de l'oxyde Eu2O3 monocristallin

Single crystals of europium oxide Eu₂O₃ with monoclinic B structure were prepared by the Verneuil process. The magnetic properties of these crystals have been studied. Paramagnetic susceptibility measurements have been performed for various orientations of the crystal with respect to the magnetic field at constant temperatures (5,77 and 300 K) as well as at increasing temperatures (5 – 1000 K). They show an anisotropy. An interpretation of this phenomenon is proposed.