Annie Pradel

Electrical properties of lithium conductive silicon sulfide glasses prepared by twin roller quenching

Abstract Glasses with the composition xLi 2 S(1-x)SiS 2 [x ⩽ 0.6] have been prepared by twin roller quenching. Their glass transition temperatures and their electrical conductivities have been measured. The conductivity reaches a maximum value of 5.10 −4 (Ω.cm) −1 at 25°C By dissolving a halide salt (LiI) in the matrix, this value has been improved to 8.2 10 −4 (Ω.cm) −1 which is almost the highest conductivity obtained with Li conductive glasses.

Ion dynamics in the argyrodite compound Ag7GeSe5I: non-Arrhenius behavior and complete conductivity spectra

Abstract The conductivity of the superionic conductor argyrodite compound Ag 7 GeSe 5 I has been measured for temperatures between 123 and 473 K and in a broad frequency range from 10 Hz to 60 GHz. The frequency-independent and frequency-dependent conductivity data have respectively been analyzed. A non-Arrhenius behavior of the dc conductivity is clearly observed. Such a behavior appears to be quite common in fast ionic conductors as if the conductivity would reach a limit value. The very complete conductivity versus frequency measurements allowed the observation of distinct regimes and the exploration of various ion-relaxation processes within the material. The conductivity spectrum can be described by superposition of several contributions: the Universal Dynamic Response due to diffusive motions, a linearly frequency-dependent regime attributed to local motions, and finally, a vibrational contribution in the far infrared domain.

Effect of rapid quenching on electrical properties of lithium conductive glasses

Abstract A twin roller apparatus has been designed to be used in a controlled environment, so that even hydroscopic and oxidizable glasses may be prepared by rapid quenching. xLi2O(1−x)P2O5 and xLi2S(1−x)GeS2 glasses have been prepared and their electrical conductivity measured as a function of temperature. The electrical characteristics of rapidly quenched and conventional glasses are compared in order to study the influence of the cooling rate. The results are quite different for oxide and sulfide glasses. Rapid quenching does not much affect oxide glasses whereas for sulfide glasses important decreases in activation energies and pre-exponential factors are observed.

Quantum confinement effects of CdS nanocrystals in a sodium borosilicate glass prepared by the sol‐gel process

Experimental evidences of both weak and strong confinement regimes are reported on CdSnanocrystals embedded in a sodiumborosilicate glass matrix. A method, based on the sol‐gel technique, is used for the preparation of CdS‐activated glass. This route is capable of providing nanocrystals covering a wide range of radii with small size dispersion. Low‐temperature linear‐absorption spectra have been analyzed in terms of excitons and electron‐hole confinements by fitting the results of a numerical calculation to experimental findings. The model used, in the envelope‐function formalism, involves both a Lorentzian broadening of the exciton energy states inside each nanocrystal and a Gaussian size distribution. The improvement of crystal quality and the sharpening of the size distribution by thermal annealing is also studied versus both time and temperature of treatment. It is shown that we can keep a tight control on the crystallinity, average size, and size distribution of the nanocrystals by rather simple adjustments and short treatments.

Percolation transition in Ag-doped germanium chalcogenide-based glasses: conductivity and silver diffusion results

Abstract Conductivity and silver diffusion measured using a 110m Ag tracer have been investigated in AgGeS and AgGeSbSe glasses with silver concentration ranging from 0.008 to 25 at.% Ag. It has been found that the room-temperature conductivity in both systems increases by 9.0–9.5 orders of magnitude with increasing silver content, and its activation energy decreases from ∼ 1 to 0.4 eV. Accordingly, the silver tracer diffusion coefficient at 298 K increases by 5.0–5.5 orders of magnitude with similar decrease of the diffusion activation energy. A comparison of the conductivity and silver diffusion results clearly shows that the ionic transport is predominant in the two systems, even at lowest Ag concentrations. The Haven ratio, H R , decreases with increasing silver content: extremely diluted glasses (0.008–0.1 at.% Ag) exhibit H R ≈ 1; Ag-rich vitreous alloys are characterized by H R = 0.2–0.4. The composition dependencies of the ionic conductivity, σ i , and silver tracer diffusion coefficient, D Ag , exhibit two drastically different transport regimes at low (≤ 2–5 at.%) and high (> 10 at.%) silver concentrations. A power-law composition dependence of σ i and D Ag over 2.5 orders of magnitude in the Ag concentration and 3.5–5.0 orders of magnitude in the ionic conductivity (2–3 orders of magnitude in the diffusion coefficient) is observed at low silver concentrations. This transport regime is attributed to percolation in the critical region just above the percolation threshold. Recent theoretical considerations (the dynamic structure model and statistical (occupation) effects on percolative ionic conduction) are also in good agreement with experimental findings. After essential structural transformations of the glass network on the short- and intermediate-range scales at higher silver content (> 10 at.%), the ionic transport is not caused any more by percolation, i.e., it becomes network-dependent with a strongly correlated motion of the Ag + ions.

Transmission measurement at 10.6μm of Te2As3Se5 rib waveguides on As2S3 substrate

The feasibility of chalcogenide rib waveguides working at λ=10.6μm has been demonstrated. The waveguides comprised a several micron thick Te2As3Se5 film deposited by thermal evaporation on a polished As2S3 glass substrate and further etched by physical etching in Ar or CF4∕O2 atmosphere. Output images at 10.6μm and some propagation losses roughly estimated at 10dB∕cm proved that the obtained structures behaved as channel waveguides with a good lateral confinement of the light. The work opens the doors to the realization of components able to work in the mid- and thermal infrared up to 20μm and even more.

Structural transformation of thiosilicate glasses: 29Si MAS-NMR evidence for edge-sharing in the system Li2SSiS2

Abstract 29Si MAS-NMR data of crystalline sodium thiosilicates show that the chemical shift differences between various Q(n) species are much smaller in sulfide, compared to the stoichiometry-analog oxide systems. On the other hand, NMR provides sensitive shift differentiation between microstructures sharing zero (E(0)), one (E(2)) and two (E(2)) edges with each other. New data reported on twin-roller quenched samples provide strong evidence for and quantitation of such edge-sharing units in Li2SSiS2 glasses. The compositional dependence of the spectra further indicates preferential attack of edge-sharing microstructures by Li2S.

Ion dynamics in superionic chalcogenide glasses studied in large frequency and temperature ranges

Abstract Electrical conductivity measurements on silver thiogermanate glasses have been performed in extended temperature (20–600 K) and frequency (10 Hz–60 GHz) ranges. The data indicate the presence of three conductivity regimes: the d.c. regime with a deviation from Arrhenius law below the glass transition temperature, a dispersive region where σ ( ω )= A ω s 1 (where s 1 ≈0.5 and A is thermally activated with an activation energy E 1 ≈(1− s ) E d.c. ) and a third regime where σ ( ω )= B ω s 2 . At T 150 K) shows clearly a superlinear frequency dependence. Additional measurements are needed to clearly identify the temperature dependence of conductivity in this region.

Realization of single-mode telluride rib waveguides for mid-IR applications between 10 and 20 μm.

The feasibility of all-telluride integrated optics devices based on waveguides presenting a single-mode behavior in the spectral range (10-20 μm) is demonstrated. These waveguides are constituted of a several micrometer thick Te(82)Ge(18) film deposited onto a Te(75)Ge(15)Ga(10) bulk glass substrate by thermal coevaporation and further etched by reactive ion etching under the CHF(3)/O(2)/Ar atmosphere. The obtained structures were proven to behave as channel waveguides with a good single-mode transmission over the whole spectral range. These results allowed validating our technological solution for the fabrication of integrated optics modal filters for spatial interferometry.

The use of ionic and mixed conductive glasses in microbatteries

Abstract This films fo conductive glasses prepared by radio-frequency sputtering or thermal evaporation were investigated. Both Li+ ionic conductive sulphide glasses and mixed conductive glasses were studied. Microbatteries were designed using these glasses as electrolytes and cathode material. They possess the following electrochemical chain: Li/Li2SSiS2(−P2S5)/V2O5TeO2 Their electrical and electrochemical characteristics were measured (open-circuit voltage 2.8–3.1 V).