Synthesis and Structural Studies of Er3+ Containing Lead Cadmium Fluoroborate Glasses and Glass-Ceramics

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Erbium L 3 -edge extended x-ray absorption fine structure ͑EXAFS͒ measurements were performed on rare earth doped fluorosilicate and fluoroborate glasses and glass ceramics. The well known nucleating effects of erbium ions for the crystallization of cubic lead fluoride ͑based on x-ray diffraction measurements͒ and the fact that the rare earth ions are present in the crystalline phase ͑as indicated by Er 3+ emission spectra͒ seem in contradiction with the present EXAFS analysis, which indicates a lack of medium range structural ordering around the Er 3+ ions and suggests that the lead fluoride crystallization does not occur in the nearest neighbor distance of the rare earth ion. Molecular dynamics simulations of the devitrification process of a lead fluoride glass doped with Er 3+ ions were performed, and results indicate that Er 3+ ions lower the devitrification temperature of PbF 2 , in good agreement with the experimental results. The genuine role of Er 3+ ions in the devitrification process of PbF 2 has been investigated. Although Er 3+ ions could indeed act as seeds for crystallization, as experiments suggest, molecular dynamics simulation results corroborate the experimental EXAFS observation that the devitrification does not occur at its nearest neighbor distance.

Section: Resultsmentioning

confidence: 99%

“…[1][2][3][4][5] This interest can be attributed to two factors. On one hand the erbium ions seem to ease the selective devitrification of ␤-PbF 2 nanoparticles in the transparent glassy matrix, decreasing the amorphous to crystalline phase transition, giving rise to transparent glass ceramics.…”

Section: Introductionmentioning

confidence: 99%

Local order around rare earth ions during the devitrification of oxyfluoride glasses

Silva

Dantelle

Mortier

et al. 2008

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“…The socalled ultratransparent glass ceramics, where metal fluorides nanocrystals are identified in the oxide glass host, can be obtained by controlled crystallization treatment. [7][8][9][10][11][12][13][14][15] These oxifluoride materials have been studied by different experimental techniques such as optical spectroscopy, transmission electron microscopy, thermal analysis, conductivity measurements, and F(1s) x-ray photoelectron spectra. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Nuclear magnetic resonance ͑NMR͒ is a wellknown experimental technique to study glass structure and ion dynamics.…”

Section: Introductionmentioning

confidence: 99%

Glass structure and ion dynamics of lead–cadmium fluorgermanate glasses

Tambelli¹,

Donoso²,

Magon³

et al. 2004

Glass structure and fluorine motion dynamics are investigated in lead-cadmium fluorgermanate glasses by means of differential scanning calorimetry, Raman scattering, x-ray absorption ͑EXAFS͒, electrical conductivity ͑EC͒, and 19 F nuclear magnetic resonance ͑NMR͒ techniques. Glasses with composition 60PbGeO 3 -xPbF 2 -yCdF 2 ͑in mol %͒, with xϩyϭ40 and xϭ10, 20, 30, 40, are studied. Addition of metal fluorides to the base PbGeO 3 glass leads to a decrease of the glass transition temperature (T g ) and to an enhancement of the ionic conductivity properties. Raman and EXAFS data analysis suggest that metagermanate chains form the basic structural feature of these glasses. The NMR study leads to the conclusion that the F-F distances are similar to those found in pure crystalline phases. Experimental results suggest the existence of a heterogeneous glass structure at the molecular scale, which can be described by fluorine rich regions permeating the metagermanate chains. The temperature dependence of the NMR line shapes and relaxation times exhibits the qualitative and quantitative features associated with the high fluorine mobility in these systems.

“…These mixed systems, composed by a well-known glass former oxide, like SiO 2 , B 2 O 3 , TeO 2 , or GeO 2 and heavy metal fluorides, can be obtained in the glassy state by the conventional melting/quenching technique, at room atmosphere. [1][2][3][4][5] In addition to the relatively simple preparation method and optical characteristics of rare earth doped samples, very interesting devitrification ͑glass crystallization͒ features are presented by these systems. For example, the MO-PbF 2 -CdF 2 systems (MOϭSiO 2 , B 2 O 3 , and GeO 2 ) are characterized by the devitrification of a cubic structure, identified as lead fluoride ␤-PbF 2 , with the possibility of obtaining transparent glass ceramics under controlled thermal treatments.…”

Section: Introductionmentioning

confidence: 99%

Molecular dynamics simulations on devitrification: The PbF2 case

Silva

Monteil

Messaddeq

et al. 2002

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In this work molecular dynamics simulations were performed to reproduce the kinetic and thermodynamic transformations occurring during melt crystallization, vitrification, and glass crystallization ͑devitrification͒ of PbF 2 . Two potential parameters were analyzed in order to access the possibility of modeling these properties. These interionic potentials are models developed to describe specific characteristic of PbF 2 , and thermodynamic properties were well reproduced by one of them, while the other proved well adapted to simulate the crystalline structure of this fluoride. By a modeled nonisothermal heat treatment of the glass, it was shown that the devitrification of a cubic structure in which the Pb-Pb distances are in good agreement with theory and experiment.