Glass structure and ion dynamics of lead–cadmium fluorgermanate glasses

Abstract

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.

Conductivity and 19F NMR in PbGeO3–PbF2–CdF2 glasses and glass-ceramics

“…Increasing the total content of fluorine ions increases the conductivities. It is known that the addition of lead fluoride also leads to a decrease of glass transition (T g ) temperatures [6][7][8][9][10][11][12][13][14][15][16] due to the formation of non-bridging fluorine atoms (NBF) substituting for bridging oxygen atoms (BO). The increase in conductivity is a consequence of the changes in the glass structure.…”

“…19 F nuclear magnetic resonance (NMR), X-ray absorption (EXAFS) and Raman scattering results have been considered in the proposal of a structural model describing these glasses by a metagermanate chain structure which permeates fluorine rich regions [16]. This particular structural model for fluorine clustering could well be extended to other oxide based hosts and explain increased mobility observed for fluorine ions and also the particular crystallization properties [2,7,15].…”

“…Glasses in the mixed system PbGeO 3 -PbF 2 -CdF 2 glasses have been studied previously [15,16] mainly considering the possibility of obtaining transparent glass ceramics. 19 F nuclear magnetic resonance (NMR), X-ray absorption (EXAFS) and Raman scattering results have been considered in the proposal of a structural model describing these glasses by a metagermanate chain structure which permeates fluorine rich regions [16].…”

Lithium dynamics in molybdenum disulfide intercalation compounds studied by nuclear magnetic resonance

“…The low temperature 19 F second moments of the glasses 60PbGeO 3 -xPbF 2 y-CdF 2 , with x + y = 40 and x = 10, 20, 30, 40 (in mol %), indicates that the fluorine ions were not uniformly distributed through the material. The NMR data, along with those of Raman and Exafs, provided the basis for a model of the glass structure at the molecular scale, described by fluorine rich regions permeating the metagermanate chain structures with F-F distances comparable to those found in crystallyne phases [25]. Figure 3 shows the temperature dependence of the 7 Li central transition line-width, without decoupling, in the three Li 0.1 MoS 2 [X] nanocomposites.…”

“…Another interesting kind of materials, where the experimental determination of the second moment provides important microscopic structural information, are the fluorogermanate glasses [25]. The low temperature 19 F second moments of the glasses 60PbGeO 3 -xPbF 2 y-CdF 2 , with x + y = 40 and x = 10, 20, 30, 40 (in mol %), indicates that the fluorine ions were not uniformly distributed through the material.…”