Verres au fluorure de scandium

New fluoride glasses deriving from ScF₃ as glass progenitor have been investigated. The best ternary compositions have been obtained within the ScF₃YF₃BaF₂ ternary system for molar compositions: 0.3–0.6 ScF₃, 0.05–0.25 YF₃, 0.35–0.50 BaF₂. For the standard SYB-4 glass (Sc₀₄Y_0.2 Ba_0.4)F_2.6, the glassy transition occurs at 360° C, melting at 720° C and two crystallization stages at 410° C and 485° C. Other physical values are 1.4985 for refractive index n_D, 4.38 for density, 180. 10^?7 K^?1 for thermal expansion coefficient. Vitreous areas have been investigated in the ScF₃BaF₂ThF₄, ScF₃BaF₂NaF, ScF₃ThF₄YF₃ and ScF₃YF₃BaF₂NaF systems. Most fluoroscandate glasses are water resistant and are continuously transparent from 300 nm in U.V. spectrum to 7000 nm in I.R. spectrum, with a classical OH band around 3000 nm, and are suitable for I.R. transmittance or medium I.R. optical fibres. Glass formation in these systems is discussed by reference to an ionic model.     

Modifications structurales de l'oxynitrure de silicium sous contraintes thermiques

Structural modifications of silicon oxynitride have been studied at high temperature up to 1200°C by time of flight neutron diffraction method. The thermal expansion along the three cristallographic axes are 1.4 ± 0.7 10^?6 deg^?1 along a, 4.4 ± 0.3 10^?6 deg^?1 along b, and 4.1 ± 0.4 10^?6 deg^?1 along c. The variation of the atomic positions are given, and also the evolution of bond angles and bond lengths between 20 and 1200°C. It is shown that the main contribution to the deformation is the evolution of the SiOSi angle which permits the rearrangement of SiN₃O tetrahedra by rotation around oxygen atoms.     

Verres aux halogenures de cadmium : I.- Verres fluores

New halide glasses based on cadmium halides as glass progenitors have been discovered. This paper describes fluoride glasses in the CdF₂-BaF₂-ZnF₂ ternary system. Binary glasses Cd_xBa_1?xF₂ (0.45 < x < 0.52) have been obtained. The limits of the glassy area are: 5–55 % CdF₂, 15–55 % BaF₂, 0–60 % ZnF₂. Numerous fluorides such as the alkali fluorides, AlF₃, YbF₃ and ThF₄ may be included in the glass composition. Only thin glass samples may be prepared because of the high crystallization rate. The characteristic temperatures of the Cd_0.3Ba_0.4Zn_0.3F₂ glass are 290° C for T_G, 330° C for T_C and 620° C for T_F. The optical transmission spectrum of a thin sample shows an extrinsic absorption band at around 9000 nm and the multiphonon IR absorption edge beyond 10500 nm. The optimization of these glasses will make them attractive materials for IR transmittance and IR optical fibres. The crystallization of the Cd_0.5Ba_0.5F₂ glass results in two solid solutions Ba_1?xCd_xF₂ and Cd_1?xBa_xF₂ deriving from the fluorite structural type. Thus, cadmium fluoride glasses appear as the result of the disordering of the fluorite type structure in the same way as ZrF₄-based glasses derive from the disordering of the ReO₃-type structure. Both glasses may be described as the random insertion of cations into an aperiodic array of F^? anions.     

Preparation and ionic conductivity of new B2S3-Li2S-LiI glasses

Glasses obtained in the B₂S₃-Li₂S-LiI system have been investigated. Ionic conductivity is higher than 10^?3Ω^?1cm^?1 at 25°C for LiI-rich glasses. The electrochemical stability range and chemical stability allow their use as solid electrolytes in solid state batteries.     

Nombre de transport et conductivite cationique dans le dioxyde de thorium: ThO2

The cationic transport number for thorium dioxide has been determined using thermal expansion measurements coupled with coulometric titration (“dilato-coulometry”). Polycrystalline ThO₂ was studied in the temperature range 1000–1500° C, under oxygen partial pressures ranging from 1 to 10^?12 atm. In air, t_Th ～ 5 × 10_?7 at 1200° C. Values for total conductivity are compared with data obtained by the Nernst-Einstein relation from the self-diffusion coefficient of Th in ThO₂.     

Etude comparative des verres AgPS3  AgX ET AgPO3  AgX avec X = I,Br

The glass-forming regions in the systems AgPS₃  AgX with X = I, Br were determined and the study of the electrical conductivity of these glasses was carried out. As observed in the AgPO₃  AgX glasses the ionic conductivity increase both with the amount of AgX and with the size of the halogen for a given concentration of AgX. The maximum value of the conductivity i.e, 10^?2 and 10^?3 (ohm cm)^?1 at 25° C for AgI and AgBr respectively, is obtained at the limit of the glass-forming region. The structural model previously described for AgPO₃  AgI systems is extended to AgPS₃  AgX glasses.     

Etude des verres fluores dans les quaternaires ZnF2ThF4AlF3MF2 (M = Mg,Ca, Sr,Ba)

Fluoride glasses have been investigated in the ZnF₂AlF₃ThF₄MF₂ (M = Ba, Sr, Ca, Mg) systems. The vitreous areas are given for the basic ternary diagrams and at a constant 40 % ZnF₂ content. Small samples may be prepared for the compositions: 40 % ZnF₂, 20 % AlF₃, 20 % ThF₄, 20 % MF₂ (M = Ba, Sr, Ca). The glassy transition occurs between 310° C and 350° C and the fusion between 650° C and 750° C. The optical transmission range lies from 240 nm to 7500 nm. The average values of refractive index, thermal expansion coefficient and density are: n_D ～ 1.48, α ～ 15.10^?6° K^?1d ～ 5. The high compactness of the anion array is compared to that of close-packed crystalline fluorides.     

Synthese et etude de la conductivite anionique des phases du systeme NaF - BiF3

A definite NaBiF₄ phase and a solid solution Na_1?xBi_xF_1+2x (0,60 ? x ? 0,70) of fluorite derived type have been obtained at 430°C in the NaF - BiF₃ system. Investigation of the electrical properties of these materials shows that Na_0,40 Bi_0,60 F_2,20 is the best anionic conductor of the system, with a conductivity of about 10^?3 Ω^?1 cm^?1 and 100°C and an activation energy of 0,46 e v. The results are discussed in comparison with those previously obtained for the KF - BiF₃ and RbF - BiF₃ systems.     

Verres fluores dans le systeme ZrF4ThF4MF3 (M = Y,Lu, Sc,Al)

The glass forming area has been precised in the ZrF₄ThF₄YF₃ ternary system. It is smaller than in the ZrF₄ThF₃LaF₃ system and corresponds to the limits: 45–70 % ZrF₄, 30–50 % ThF₄, 0–12 % YF₃. A series of glass samples with molar composition 0.5 ZrF₄, 0.43 ThF₄, 0.07 MF₃ (M : La, Y, Lu, Sc, Al) has been prepared and the linear evolution of T_G, molar refractivity and anionic compactness versus the ionic radius of M³⁺ is shown. The thermomechanical properties are better than for previous fluorozirconate glasses including barium. The average values are 480° C for T_G, 580° C for T_C, 800° C for T_F, 1.54 for n_D, 90.10^?7 K^?1 for thermal expansion coefficient. The U.V. absorption edge is improved by comparison with standard ZrF₄ -and AlF₃- based glasses. The potential application to I.R. optical fibres is discussed.     

Mechanochemical synthesis of SnO-B2O3 glassy anode materials for rechargeable lithium batteries

The xSnO·(100 ? x)B₂O₃ (0 ≦ x ≦ 80) glasses were successfully prepared by a mechanical milling technique. The glass with 40 mol% SnO showed the maximum glass transition temperature of 347°C. The SnO-B₂O₃ milled glasses consisted of both BO₃ and BO₄ units, and the fraction of BO₄ units was maximized at the composition of 50 mol% SnO. The electrochemical properties of the milled glasses were examined using a simple three electrodes cell with a conventional liquid electrolyte. The glasses with high SnO content exhibited high charge capacities more than 1100 mAh g^?1 and discharge capacities more than 700 mAh g^?1 at the first cycle. The SnO-B₂O₃ milled glasses proved to work as anode materials for rechargeable lithium batteries.     

Conductivite ionique dans les verres LiPO3LiX (X = I,Br, Cl)

The glass-forming regions in the systems LiPO₃LiX with X = I, Br, Cl were determined and the study of the electrical conductivity of glasses belonging to these systems was carried out. The conductivity increases with increasing halogen ion size and reaches maxima values of the order of 10^?6, 3, 2 10^?7, 10^?7 (ohm cm)^?1 at 25° C with LiI, LiBr, LiCl respectively : they are obtained at the limit of glass forming region. The Raman spectra do not show any modifications. The study of the electrical conductivity shows that the conduction is essentially ionic in nature.     

Structural relaxation and electrical conductivity of molybdovanadate glass

⁵⁷Fe Mössbauer spectrum of conductive barium iron vanadate glass with a composition of 20BaO·10Fe₂O₃·70V₂O₅ (in mol%) showed paramagnetic doublet peak due to distorted Fe^IIIO₄ tetrahedra with isomer shift (δ) value of 0.37 (±?0.01) mm s^?1. Mössbauer spectra of 20BaO·10Fe₂O₃·xMoO₃·(70???x)V₂O₅ glasses (x?=?20–50) showed paramagnetic doublet peaks due to distorted Fe^IIIO₆ octahedra with δ’s of 0.40–0.41 (±?0.01) mm s^?1. These results evidently show a composition-dependent change of the 3D-skeleton structure from “vanadate glass” phase, composed of distorted VO₄ tetrahedra and VO₅ pyramids, to “molybdate glass” composed of distorted MoO₆ octahedra. After isothermal annealing at 500 °C for 60 min, Mössbauer spectra also showed a marked decrease in the quadrupole splitting (Δ) of Fe^III from 0.70 to 0.77 to 0.58–0.62 (±?0.02) mm s^?1, which proved “structural relaxation” of distorted VO₄ tetrahedra which were randomly connected to FeO₄, VO₅, MoO₆, FeO₆ and MoO₄ units by sharing corner oxygen atoms or edges. DC-conductivity (σ) of barium iron vanadate glass (x?=?0) measured at room temperature was 3.2?×?10^?6 S cm^?1, which increased to 3.4?×?10^?1 S cm^?1 after the annealing at 500 °C for 60 min. The σ’s of as-cast molybdovanadate glasses with x’s of 20–50 were ca. 1.1?×?10^?7 or 1.2?×?10^?7S cm^?1, which increased to 2.1?×?10^?2 (x?=?20), 6.7?×?10^?3 (x?=?35) and 1.9?×?10^?4 S cm^?1 (x?=?50) after the annealing at 500 °C for 60 min. It was concluded that the structural relaxation of distorted VO₄ tetrahedra was directly related to the marked increase in the σ, as generally observed in several vanadate glasses.     

Preparation of ZrF4-NaF-BaF2-LaF3-YbF2 glasses with YbF2 substitution for BaF2 (LaF3)

We have prepared glasses and semicrystalline phases with a green color in the systems ZrF₄(53.5)-NaF(20)-BaF₂(20)-LaF₃(6.5 ? x)-YbF₂(x) (0 ≤ x ≤ 6.5 mol %) (I) and ZrF₄(53.5)-NaF(20)-BaF₂(20 ? x)-LaF₃(6.5)-YbF₂(x) (0 ≤ x ≤ 20 mol %) (II). Thermal analysis results demonstrate that, in both systems, the glass transition temperature of the samples containing ≤3 mol % YbF₂ lies in the range 200–250°C, their heating curves show two or three crystallization events (at 320–340, 380–460, and 415–490°C), and their melting points range from 460 to 490°C. Increasing the YbF₂ content of the glasses to 4 mol % and above (system I) has no effect on their glass transition temperature, reduces the temperature of the first crystallization event from 340 to 305°C, and produces extra peaks in the range 545–600°C, above the major melting peak, which can be accounted for by a nonequilibrium state of the glasses. Ytterbium difluoride substitution for barium difluoride (10 to 20 mol %) (system II) leads to the formation of semicrystalline phases and increases the glass-transition (305°C), crystallization (470–515°C), and melting (570–690°C) temperatures. The IR spectra of such samples show, in addition to a so-called “featureless continuum” (～500 cm^?1), absorption bands characteristic of the Yb-F bond. Electronic spectra also confirm that the glasses contain both divalent and trivalent ytterbium.     

Anion conduction in fluorozirconate glasses

Fluorozirconate glasses have been prepared and their ionic conductivity measured as a function of composition and temperature. All compositions are good fluoride ion conductors with conductivities at 250°C in the 10^?6–10^?5 (Ω-cm)^?1 range and activation energies between 0.7 and 0.9 eV. The fluoride ion to metal ratio was varied in the ZrF₄/1bBaF₂/1bThF₄/1bNaF system by replacing ZrF₄and/or BaF₂ with NaF. When Na⁺ substitutes for Ba⁺² a systematic decrease in the conductivity, σ, and the activation energy, E_a, is seen. This is explained on the basis of a reduction of carriers and on the modification of the network by Na⁺ ions. No systematic variation in σ or E_a were seen when Na⁺ replaces Zr⁺⁴. A change in slope of the log σ vs 1/T plot was seen at the glass transition temperature in La-containing glasses.     

Conductivite electrique et spectres de diffusion raman des verres mixtes AgPO3 − MI2 AVEC M = Cd,Hg, Pb. Correlation entre conductivite et structure

The glass-forming regions in the AgPO₃ ? MI₂ systems with M = Cd,Pb,Hg were determined. Electrical conductivity measurements and Raman spectra were carried out. A maximum conductivity value of $\text{10}{}^{\mathrm{?2}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 25°C is obtained for a mole fraction of 0,19 in PbI₂ or in CdI₂, whereas a value of $\text{3×10}{}^{\mathrm{?5}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 25°C is found for a mole fraction of 0,5 in HgI₂. The conductivity results and Raman spectra are examined and compared with those of AgPO₃ ? AgI. An exchange between Ag⁺ and M²⁺ ions is proposed leading to AgI species in AgPO₃ ? CdI₂ and AgPO₃ ? PbI₂ glasses. It could explain the high conductivity values obtained and the similarities observed in Raman spectra.     

Structure et conductivite electrique de verres appartenant au systeme Li2Si2O5 Li2SO4

The conductivity of vitreous electrolytes belonging to the Li₂Si₂O₅ Li₂SO₄ system has been measured over the temperature range 25–300 °C and for Li₂SO₄ concentrations varying from 0–28 mole percent. It has been found that the conductivity increases with the Li₂SO₄ fraction, attaining 10^?5 Ω^?1 cm^?1 at 130°C for the glass containing the highest proportion of sulphate. Raman spectroscopic studies indicate that the tetrahedral SO^2?₄ ions are in the glassy network, inserted or not into the silicate chains.     

Study on properties of forsterite/cordierite ceramic composites

The forsterite/cordierite ceramic composites are prepared by standard ceramic method, which properties and microstructures are characterized by X-ray diffraction and Scanning electron microscopy. It is found that the values of volume resistivities rapidly decline from 1 × 10¹³ to 10³ Ω cm as the testing temperatures increase from 20 to 600 °C and the resistivity transition temperatures of forsterite, cordierite and their composites are at about 300, 200 and 250 °C, respectively. The values of ε _r and tan δ are somewhat independent of the temperatures between 20 and 200 °C, but increase rapidly between 200 and 600 °C. The thermal expansion coefficient of ceramic composites decline with the cordierite content increasing and could change from about 2.5 × 10^?6–10.5 × 10^?6 °C^?1, in which the major phases are Mg₂SiO₄ and Mg₂Al₄Si₅O₁₈.     

Bi2MoO6 dielectric thin films fabricated by thermal oxidation of Bi/Mo thin films at ultra-low temperature

Bi/Mo multilayer thin films are deposited on Si/SiO₂/Pt substrates by direct current magnetron sputtering. The effect of annealing temperature on the microstructure, dielectric and electrical properties of the as-sputtered films is characterized systematically. X-ray diffraction data indicate that the films annealed at 450–600 °C are a mixture of diphase with the main phase Bi₂MoO₆ and secondary phase Bi₂Mo₂O₉. Results of scanning electron microscope observation show that the films annealed at 500–550 °C are dense and uniform, in particular the films annealed at 500 °C exhibit optimal dielectric and electrical properties with dielectric constant as high as 37.5, dielectric loss 1.06 %, temperature coefficient of dielectric constant ?10.86 ppm °C^?1 at 1 kHz, and leakage current density of 1.46 × 10^?7 A mm^?2 at an electric field of 18.2 kV mm^?1. With the advantages of ultralow densification temperature (500 °C) and very high sputtering deposition rate (76 nm min^?1), it is anticipated that thermal oxidation method of the sputtered Bi/Mo thin films could be a promising technique for fabrication of Bi₂MoO₆ ceramic thin film embedded-capacitors.     

Effet Hall dans les films d'argent déposés par voie chimique

Study of the Hall effect on silver films prepared by chemical reduction shows an electronic conductivity. At 25°C the Hall coefficient R_H is ?(12 ± 1) × 10^?11 m³ C^?1 and the number of conduction electrons n = 0.89 electrons per atom agrees within 10% of the result obtained from measurement of the conductivity.The mobility of the electron transport in the annealed films, μ_Hr(25°C) = 4.85 × 10^?3 m²V^?1s^?1 is six to seven time greater than that of the same unannealed films, μ_Hi(25°C) = 0.75 × 10^?3 m² V^?1 s^?1.