Zeolites versus aluminosilicate clusters: the validity of a local description

Kramer, GJ Gert Jan; Man, de Ajm Andries; Santen, van Ra Rutger

doi:10.1021/ja00017a012

Cited by 190 publications

(136 citation statements)

References 0 publications

Supporting

Mentioning

125

Contrasting

Order By: Relevance

“…The new parameters, devoted to describe the interactions between the sodium atoms and the silica network are given by Kramer et al 25 and are adjusted on ab initio calculations of zeolithes except the partial charge of the sodium atoms whose value q Na = 0.6e is chosen in order to respect the system electroneutrality. However, this sodium partial charge does not reproduce the short-range forces and to this purpose, Horbach et al 22 have proposed to vary the charge q Na as follows:…”

Section: Methodsmentioning

confidence: 99%

Sodium diffusion through amorphous silica surfaces: A molecular dynamics study

Rarivomanantsoa

Jund

Jullien

2004

The Journal of Chemical Physics

View full text Add to dashboard Cite

We have studied the diffusion inside the silica network of sodium atoms initially located outside the surfaces of an amorphous silica film. We have focused our attention on structural and dynamical quantities, and we have found that the local environment of the sodium atoms is close to the local environment of the sodium atoms inside bulk sodo-silicate glasses obtained by quench. This is in agreement with recent experimental results.

show abstract

Section: Methodsmentioning

confidence: 99%

Sodium diffusion through amorphous silica surfaces: A molecular dynamics study

Rarivomanantsoa

Jund

Jullien

2004

The Journal of Chemical Physics

View full text Add to dashboard Cite

show abstract

“…Although it is a simple pair potential, it has been shown to reproduce very well many static and dynamic properties of amorphous silica [31,32,33,34,8,35,36,37,38,39,40,41,42,43,44]. An extension of the BKS potential that allows to consider also mixtures of silica with other oxides such as Na 2 O and Al 2 O 3 was proposed by Kramer et al [45]. As demonstrated recently [46,47,14,48,15,13,49,50], this potential gives also a quite realistic description of the static and dynamic properties of sodium silicates.…”

Section: Model and Details Of The Simulationmentioning

confidence: 97%

“…Unfortunately in Ref. [45], the q α 's were fixed such that systems like AS2 are not neutral: q O = −1.2, q Si = 2.4, and q Al = 1.9. Only with the additional component phosphorus the system recovers charge neutrality according to the parameter sets in Ref.…”

Section: Model and Details Of The Simulationmentioning

confidence: 99%

Structure and diffusion in amorphous aluminum silicate: A molecular dynamics computer simulation

Winkler

Horbach

Kob

et al. 2004

The Journal of Chemical Physics

118

128

View full text Add to dashboard Cite

The amorphous aluminium silicate (Al2O3)2(SiO2) [AS2] is investigated by means of large scale molecular dynamics computer simulations. We consider fully equilibrated melts in the temperature range 6100 K ≥ T ≥ 2300 K as well as glass configurations that were obtained from cooling runs from T = 2300 K to 300 K with a cooling rate of about 10 12 K/s. Already at temperatures as high as 4000 K, most of the Al and Si atoms are four-fold coordinated by oxygen atoms. Thus, the structure of AS2 is that of a disordered tetrahedral network. The packing of AlO4 tetrahedra is very different from that of SiO4 tetrahedra in that Al is involved with a relatively high probability in small-membered rings and in triclusters in which an O atom is surrounded by four cations. We find as typical configurations two-membered rings with two Al atoms in which the shared O atoms form a tricluster. On larger length scales, the system shows a microphase separation in which the Al-rich network structure percolates through the SiO2 network. The latter structure gives rise to a prepeak in the static structure factor at a wavenumber q = 0.5Å −1 . The comparison of experimental X-ray data with the results from the simulation shows a good agreement for the structure function. The diffusion dynamics in AS2 is found to be much faster than in SiO2. We show that the self-diffusion constants for O and Al are very similar and that they are by a factor of 2-3 larger than the one for Si.

show abstract

“…2.38 g.cm −3 [16]. The interactions between the particles are given by a modified version of the socalled "BKS" potential [17,18] which is able to reproduce the structure as well as the dynamics of several sodiumsilicate systems [10][11][12][13]19] (for more details see [11]). In the present study we have generated three independent samples (in the following, all the results are averaged over these samples in order to improve the statistics) at a temperature of ∼ 1900 K for which the channels have been evidenced in our previous studies.…”

mentioning

confidence: 99%

Matrix-controlled channel diffusion of sodium in amorphous silica

Sunyer

Jund

Jullien

2003

J. Phys.: Condens. Matter

View full text Add to dashboard Cite

To find the origin of the diffusion channels observed in sodium-silicate glasses, we have performed classical molecular dynamics simulations of Na2O-4SiO2 during which the mass of the Si and O atoms has been multiplied by a tuning coefficient. We observe that the channels disappear and that the diffusive motion of the sodium atoms vanishes if this coefficient is larger than a threshold value. Above this threshold the vibrational states of the matrix are not compatible with those of the sodium ions. We interpret hence the decrease of the diffusion by the absence of resonance conditions. PACS numbers: 61.43. Fs, 61.43.Bn, 66.30.Hs, 63.50.+x The mechanism of ionic transport in amorphous materials [1,2] at the atomic scale is not completely elucidated so far and therefore it is the subject of numerous experimental [3,4] and numerical [5][6][7][8][9] studies. Among the most studied systems are the sodium-silicate glasses since they contain the essential ingredients, namely the amorphous matrix (silica) and the mobile ions (sodium), as a first step in the simulation of more complex glasses of higher practical interest.In previous studies [10-12], we have shown by means of classical molecular dynamics simulations of Na 2 O-4SiO 2 (NS4), that the sodium atoms diffuse through a well connected network of pockets (which represents only a limited fraction of the entire available space) that we have called "channels" to be coherent with the literature. The existence of the channels, which are not due to microsegregation effects [6,7], has been confirmed by the existence of a pre-peak in the partial Na-Na structure factor at a wave-vector q = 0.95Å −1 [13]. This pre-peak has also been observed experimentally [14] and numerically [15] in another study. We have also shown that the location of the channels is strongly correlated to the positions of the non-bridging oxygens [13] and Horbach et al. have shown that the sodium dynamics should be related to that of the underlying silica network [15]. This suggests that the origin of the channels could be related to the dynamical properties of the matrix. To check this idea we present in this letter classical molecular dynamics simulations on a series of "toy" systems in which the atomic masses of both the oxygen and silicon atoms have been systematically changed after artificially multiplying their experimental values by a common factor µ varying from 0.5 to infinity, the usual NS4 system being recovered for µ = 1.By studying both the mean square displacement of the sodium atoms and the characteristics of the channels, we find a change in the sodium diffusion properties when the parameter µ is increased above a value of about 30. Above this threshold, the sodium diffusion decreases and the channels can no more be clearly defined. Guided by the concomitant change in the short time characteristics of the velocity autocorrelation function, we have calculated the vibrational density of states (VDOS) for both the sodium atoms and the atoms of the matrix for various values of µ. We obse...

show abstract

Zeolites versus aluminosilicate clusters: the validity of a local description

Cited by 190 publications

References 0 publications

Sodium diffusion through amorphous silica surfaces: A molecular dynamics study

Sodium diffusion through amorphous silica surfaces: A molecular dynamics study

Structure and diffusion in amorphous aluminum silicate: A molecular dynamics computer simulation

Matrix-controlled channel diffusion of sodium in amorphous silica

Contact Info

Product

Resources

About