A molecular dynamics model of the atomic structure of dysprosium alumino-phosphate glass

Martin, Richard A.; Mountjoy, Gavin; Newport, Robert J.

doi:10.1088/0953-8984/21/7/075102

Cited by 16 publications

(8 citation statements)

References 40 publications

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“…16 Similar settings were subsequently adopted in a significant number of MD simulation studies targeting a wide variety of modified silicate and phosphate glasses. [17][18][19][20][21] The high quality of atomistic models obtained using MD with these settings confirmed their good transferability to systems more complex than a-SiO 2 , and for this reason they can generally be considered the "standard" for MD simulations of glasses, essentially representing a wellestablished reference to which other conditions could be compared.…”

Section: Introductionmentioning

confidence: 91%

Cooling rate and size effects on the medium-range structure of multicomponent oxide glasses simulated by molecular dynamics

Tilocca¹

2013

The Journal of Chemical Physics

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A set of molecular dynamics simulations were performed to investigate the effect of cooling rate and system size on the medium-range structure of melt-derived multicomponent silicate glasses, represented by the quaternary 45S5 Bioglass composition. Given the significant impact of the glass degradation on applications of these materials in biomedicine and nuclear waste disposal, bulk structural features which directly affect the glass dissolution process are of particular interest. Connectivity of the silicate matrix, ion clustering and nanosegregation, distribution of ring and chain structural patterns represent critical features in this context, which can be directly extracted from the models. A key issue is represented by the effect of the computational approach on the corresponding glass models, especially in light of recent indications questioning the suitability of conventional MD approaches (that is, involving melt-and-quench of systems containing ~10(3) atoms at cooling rates of 5-10 K/ps) when applied to model these glasses. The analysis presented here compares MD models obtained with conventional and nonconventional cooling rates and system sizes, highlighting the trend and range of convergence of specific structural features in the medium range. The present results show that time-consuming computational approaches involving much lower cooling rates and/or significantly larger system sizes are in most cases not necessary in order to obtain a reliable description of the medium-range structure of multicomponent glasses. We identify the convergence range for specific properties and use them to discuss models of several glass compositions for which a possible influence of cooling-rate or size effects had been previously hypothesized. The trends highlighted here represent an important reference to obtain reliable models of multicomponent glasses and extract converged medium-range structural features which affect the glass degradation and thus their application in different fields. In addition, as a first application of the present findings, the fully converged structure of the 45S5 glass was further analyzed to shed new light on several dissolution-related features whose interpretation has been rather controversial in the past.

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Section: Introductionmentioning

confidence: 91%

Cooling rate and size effects on the medium-range structure of multicomponent oxide glasses simulated by molecular dynamics

Tilocca¹

2013

The Journal of Chemical Physics

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“…Classical molecular dynamics simulations have been applied extensively to the simulation of phosphosilicate glasses [11][12][13][14][15][16] and binary phosphate glasses. [17][18][19][20][21][22][23][24][25] However only very recently, a polarizable interatomic forceeld has been developed to model ternary CaO-Na 2 O-P 2 O 5 systems. 26 An alternative computational approach is the ab initio molecular dynamics (AIMD) technique, 27 which is usually based on density functional theory.…”

Section: Introductionmentioning

confidence: 99%

Modelling the structural evolution of ternary phosphate glasses from melts to solid amorphous materials

et al. 2013

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The local and medium-range structural properties of phosphate-based melts and glasses have been characterized by means of first principles (density functional theory) and classical (shell-model) molecular dynamics simulations. The structure of glasses with biomedically active molecular compositions, (P 2 O 5) 0.45 (CaO) x (Na 2 O) 0.55Àx (x ¼ 0.30, 0.35 and 0.40), have been generated using first principles molecular dynamics simulations for the full melt-and-quench procedure and the changes in the structural properties as the 3000 K melt is cooled down to room temperature have been compared extensively with those of the final glasses. The melts are characterized by a significant fraction of threefold (P 3c) and fivefold (P 5c) phosphorus atoms, but structural defects rapidly decrease during the cooling phase and for temperatures lower than 1800 K the system is free of under-and overcoordinated species. The analysis of the structures of the glasses at 300 K shows a prevalence of the metaphosphate Q 2 and pyrophosphate Q 1 species, whereas the number of Q 3 units, which constitute the three-dimensional phosphate network, significantly decreases with the increase of calcium content in the glass. The radial and angular distribution functions indicate that higher calcium concentration in the glass leads to an increase of the rigidity of the phosphate tetrahedral network, which has been explained in terms of the calcium's higher field strength compared to that of sodium. The structural characterization of the melts and glasses obtained from first principles simulations was used to assess and validate a recently developed interatomic shell-model forcefield for phosphate-based materials. For all three compositions, our potential model is in good agreement with the first principles data. In the glass network, the forcefield provides a very good description of the split between the shorter distances of phosphorus to non-bonded oxygen and the longer distances of the phosphorus to bonded oxygen; the phosphorus-phosphorus medium-range distribution; and the coordination environment around the Na and Ca glass modifiers. Moreover, the distribution of the Q n species in the melts and glasses is in excellent agreement with the values extracted from the first principles simulations. In contrast, simulations using standard rigid ion potentials do not provide a satisfactory description of the local short-range structure of phosphate-based glasses and are therefore less suitable to model this class of multicomponent amorphous system.

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“…RE ions tend to form clusters in silica glass. Doping silica with aluminum or phosphorus oxides has been shown to be effective in declustering of RE ions 17,18,48 . It is generally accepted that, due to their high field strength, RE ions form clusters to share nonbridging oxygen ions, thus satisfying their coordination requirements in rigid silicon–oxygen network structures.…”

Section: Introductionmentioning

confidence: 99%

Structure of Cerium Phosphate Glasses: Molecular Dynamics Simulation

Kokou

Rygel

et al. 2011

Journal of the American Ceramic Society

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We performed molecular dynamics (MD) simulations of the structure and properties of cerium-containing phosphosilicate, aluminophosphate, and aluminophosphosilicate glasses based on recent spectroscopic data that revealed 95% of cerium ions in such glasses are Ce 31 . New Ce 31 -and Ce 41 -O 2À potentials were developed and used in the MD simulations of these ceriumcontaining glasses with mixed glass formers. The local environments around cerium ions and network-forming cations, the medium range structure including glass-forming network Q n distribution, clustering, and second coordination shell around cerium ions have been carefully characterized. The results showed a longer Ce-O bond length and larger coordination number for Ce 31 than Ce 41 (2.48 and 6.4 vs. 2.24Å and 5.8, respectively). Around 5% of Si 41 ions were found to be in fivefold and sixfold coordination states in cerium phosphosilicate glasses, rather than the usual fourfold in silicate glasses. At the same time, the silicon-oxygen polyhedra were highly polymerized (over 80% of Q 4 ) due to the presence of phosphorus oxide. Aluminum ions were found to be coordinated by four-, five-, and six oxygen ions, with an average coordination number of around 4.2. In both oxidation states, cerium ions were found to be preferentially surrounded by phosphorus-oxygen tetrahedra, which form a kind of solvation shell around them. The preference of network-forming cations around cerium ions in the second coordination shell was found to decrease in the sequence phosphorus, aluminum, silicon.

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A molecular dynamics model of the atomic structure of dysprosium alumino-phosphate glass

Abstract: The version in the Kent Academic Repository may differ from the final published version. Users are advised to check http://kar.kent.ac.uk for the status of the paper. Users should always cite the published version of record.

Cited by 16 publications

References 40 publications

Cooling rate and size effects on the medium-range structure of multicomponent oxide glasses simulated by molecular dynamics

Cooling rate and size effects on the medium-range structure of multicomponent oxide glasses simulated by molecular dynamics

Modelling the structural evolution of ternary phosphate glasses from melts to solid amorphous materials

Structure of Cerium Phosphate Glasses: Molecular Dynamics Simulation

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