M. Poulain

Crystallization in fluoride glasses. I: Devitrification on reheating

Abstract The devitrification of glass from the BaF 2 LaF 3 ZrF 3 AlF 3 quaternary system is studied as a function of sample size and heating rate by differential scanning calorimetry. Results are analyzed in terms of a theory of non-isothermal crystallization kinetics similar to that of Matusita and Sakka but modified to allow for diffusion controlled growth of the crystallites.

F− ion conductivity and diffusion properties in ZrF4-based fluoride glasses with various NaF concentrations (0 ⩽ xNaF ⩽ 0.45)

Abstract Selecting two series of ZrF 4 -based fluoride glasses containing at the same time the BaF 2 and NaF network modifiers and a third series with NaF only, an investigation of electrical and diffusion properties has been undertaken as a function of x NaF in a wide concentration domain (0 ⩽ x NaF ⩽ 0.45). The ac conductivity data have been analysed by the complex modulus formalism and a hopping mechanism for transport in these materials is suggested. The 23 Na and 19 F NMR investigations have shown that Na + ions do not participate as charge carriers in the conduction mechanisms and the diffusion properties are due only to motions of mobile F − ions. Mobility and number of F − ions mobile in the NMR time scale increase when x BaF 2 increases, result in agreement with the composition dependence of electrical properties at long range. Experimental points representative of log σ 473 K and ΔE σ as a function of x NaF for the glasses studied are located on both sides of “master” curves involving a conductivity minimum and an activation energy maximum for x NaF ∼- 0.30. Variation of the decoupling index, R τ ( T g ), with x NaF is in agreement with that of σ 473 K in the whole of the studied composition. On the contrary, the variation of the Kohlrausch parameter, β, is more difficult to analyse and may be explained by the coupling model only for x NaF ≲ 0.15. The variation of various electrical parameters is discussed as a function of glass composition.

SiO2–PbF2–CdF2 glasses and glass ceramics

Abstract Lead–Cadmium fluorosilicate stable glasses were prepared and the vitreous domain region determined in the composition diagram. Characteristic temperatures were obtained from thermal analysis and the structural studies performed illustrate clearly the role played by lead atoms in the glasses crystallization behavior and the glass-forming ability of cadmium atoms. The occurrence of either a cubic lead fluoride or a lead–cadmium fluoride solid solution in crystallizing samples was found to be dependent on Er3+ doping. The optically active ions were found to concentrate in the crystalline phase and in fact play the role of nucleating agent as suggested from X-ray diffraction and EXAFS measurements.

Ionic conductvity and NMR investigation of quaternary glasses in the ZrF4BaF2ThF4LiF system

Abstract The existence of glasses involving large amounts of LiF (up to 60%) within the ZrF4BaF2ThF4LiF quaternary systems has allowed the authors to study the evolution of transport properties with varying LiF content. A minimum of ionic conductivity bound to a maximum of activation energy has been detected when the atomic Li/F ratio is equal to ≅ 0.07. In the Li-low concentration domain, σ increases regularly and ΔE decreases simultaneously when the BaF2 concentration increases; on the contrary in the Li-high concentration region log σ and ΔE are quasi-linear functions, increasing and decreasing respectively, of the LiF rate. A 7Li and 19F NMR investigation has shown that Li+ and F− ions are simultaneously mobile and the temperature dependence of the number of mobile F− ions has been determined. In the Li-low concentration domain transport properties result from mixed contributions of mobile Li+ and F− ions, for high Li concentrations they depends only on the Li+ rate. Glasses with high Li-content have good electrical performnces (e.g. σ175°C ≅ 2.10−4ω−1 cm−1 for Zr0.20Ba0.10Li0.60Th0.10F2).

Influence of network modifiers on conductivity and relaxation parameters in some series of fluoride glasses containing LiF

Abstract A new series of fluoride glasses of formulation ZrF 4 (0.25)-ZnF 2 (0.15)-YF 3 (0.05)-AlF 3 (0.10)-CdF 2 (0.17 − 2x 5 )-BaF 2 (0.28 − 3x 5 )-LiF(x) and containing a wide LiF concentration range (0 ≤ xLiF ≤ 0.35) has been investigated by impedance spectroscopy: the variation of various electrical parameters has been determined as a function of composition. The results obtained with two other series of fluoride glasses covering the (0 ≤ xLiF ≤ 0.30) and (0.20 ≤ xLiF ≤ 0.60) concentration ranges are confirmed. A conductivity minimum associated with an activation energy maximum and a minimum of the decoupling index Rτ(Tg) takes place for xLiF ∼- 0.20. It is explained by the crossing with increasing x from a conductivity due preferentially to F− ions to a conductivity due preferentially to Li+ ions. Within each series, the composition relative to conductivity minimum offers a value r ⋍ 1 of the ( x LiF x BaF 2 ) ratio. For higher xLiF rates, the β conductivity relaxation parameter involves also a minimum. Comparison of various series studied indicates that the composition relative to β minimum offers a value r ⋍ 2 of the ( x LiF x BaF 2 ) ratio. The structural origin of the β minimum is confirmed.

New fluoroindate glass compositions

Abstract Fluoroindate glasses are potential new materials for the fabrication of IR fibers with extended spectral range. InF3SrF2BaF2ZnF2X glass compositions, where X = PbF2, CdF2, NaF and CaF2, have been prepared in a glove box using a conventional method and their phase diagrams have been determined. The addition of small quantities of GdF3 improves the stability of these compositions. Optical and thermal properties of these glasses are reported.

Frequency upconversion in a Pr3+ doped chalcogenide glass containing silver nanoparticles

We report on orange-to-blue frequency upconversion (UC) in Pr3+ doped chalcogenide glass (Ga10Ge25S65) doped with Ag2S and heat treated under different conditions to nucleate silver nanoparticles (NPs). The experiments were performed using 7ns pulses from a dye laser that operates at ∼590nm, in resonance with the H43→D21 transition of Pr3+ ions. The enhancement observed in the UC emission at ∼494nm, ascribed as P03→H43 transition of the Pr3+ ion, is attributed to the large local field acting on the emitting ions due to the presence of the metallic NPs.

Transport properties of ZrF4BaF2LaF3AF (A = Li, Na) glasses

A comparative study of electrical properties of two series of glasses ZrF4(0.62−0.4x)BaF2(0.30−0.5x)LaF3(0.08−0.1x)AF(x) (A = Li, Na) (0 < x < 0.30) has been carried out as a function of AF content. A minimum of ionic conductivity and a maximum of activation energy has been detected when the atomic Li/F ratio is equal to ≅ 0.07. By analogy with the glasses belonging to ZrF4BaF2ThF4LiF system, it is proposed that in the low concentration Li domain Li/F ⪆ 0.07) , they properties result from mixed contributions of mobile Li+ and F− ions and for high Li concentrations (Li/F ⪆ 0.07), they depend only on the Li+ rate. When A = Na, on the contrary, conductivity decreases regularly and activation energy increases with increasing x. The electrical properties result only from the contribution of mobile F− ions. A 23Na NMR study has shown that Na+ ions do not participate in the conductivity.

New alkali antimonate glasses

Abstract Glass formation has been investigated in ternary systems Sb 2 O 3 –PbO–M 2 O in which M is alkali Li, Na and K and antimony oxide is the glass former. Alkali elements were introduced as carbonates. The size of the glass forming region is enlarged as alkali ionic radius increases. Binary Sb 2 O 3 –M 2 O glasses were obtained: (100− x ) Sb 2 O 3 – x Li 2 O, (10 x x ) Sb 2 O 3 – x Na 2 O, (10 x x ) Sb 2 O 3 – x K 2 O, (10 x T g , onset of crystallization, T x , and maximum of crystallization, T p , have been measured using differential scanning calorimetry. Depending on composition, glass transition temperature ranges from 240 to 330 °C. The incorporation of alkali oxide increases T g while lead oxide has the reverse effect. Thermal stability range ( T x – T g ) was usually between 65 and 266 °C, while no crystallization exotherm was observed in some cases. Density and thermal expansion increases as lead concentration increases. Optical transmission has been measured. The UV cut-off depends on alkali content: samples are yellow and turn green for large K and Na content. These glasses have potential applications as low phonon energy glasses for infrared transmission or active devices.

Systematic substitutions in ZBLA and ZBLAN glasses

Starting from ZBLA and ZBLAN glasses, the following substitutions were implemented: CdF 2 /BaF 2 , KF/BaF 2 in ZBLA, KF/NaF and RbF/NaF in ZBLAN 14, PbF 2 /BaF 2 in ZBLAN 20. Basic glass compositions are: 57ZrF 4 -34BaF 2 -5LaF 3 -4AlF 2 , 54ZrF 4 -24BaF 2 -4LaF 3 -4lF 3 -14NaF and 52ZrF 3 -20BaF 2 -4LaF 3 -4AlF 3 -20NaF. The evolution of physical properties versus composition is reported. Some non-linear evolutions were observed