Direct evidence of rigidity loss and self-organization in silicate glasses (original) (raw)
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Direct evidence of rigidity loss and self-organisation in silicate glasses
2004
The Brillouin elastic free energy change DFDFDF between thermally annealed and quenched (Na2O)x(SiO2)1−x(Na_2O)_x(SiO_2)_{1-x}(Na2O)x(SiO2)1−x glasses is found to decrease linearly at x>0.23x > 0.23x>0.23 (floppy phase), and to nearly vanish at x<0.18x < 0.18x<0.18 (stressed- rigid phase). The observed DF(x)D F(x)DF(x) variation closely parallels the mean-field floppy mode fraction f(x)f(x)f(x) in random networks, and fixes the two (floppy, stressed-rigid) elastic phases. In calorimetric measurements, the non-reversing enthalpy near TgT_gTg is found to be large at x<0.18x < 0.18x<0.18 and at x>0.23x > 0.23x>0.23, but to nearly vanish in the 0.18<x<0.230.18 < x < 0.230.18<x<0.23 range, suggesting existence of an intermediate phase between the floppy and stressed-rigid phases.
Structure and Topology of Soda-Lime Silicate Glasses: Implications for Window Glass
The Journal of Physical Chemistry B, 2014
The structural and topological properties of soda-lime silicate glasses of the form (1−2x)SiO 2 −xNa 2 O−xCaO are studied from classical molecular dynamics using a Buckingham type potential. Focus is made on three compositions (x = 6%, 12%, and 18%) which are either silica-rich or modifier-rich. We compare the results to available experimental measurements on structural properties and find that the simulated pair correlation function and total structure factor agree very well with available experimental measurements from neutron diffraction. The detail of the structural analysis shows that the Na and Ca coordination numbers tend to evolve with composition, and with increasing modifier content, changing from 5.0 to 5.6 and from 4.0 to 5.0 for Ca and Na, respectively. The analysis from topological constraints shows that the picture derived on a heuristic basis using classical valence rules remains partially valid. Ultimately, typical elastic phases are identified from the application of rigidity theory, and results indicate that the 6% system is stressed-rigid, whereas the modifier-rich composition (18%) is flexible. These results receive support from a full analysis of the vibrational density of states showing the low-energy bands at E < 20 meV increase as the system becomes flexible, providing another indirect signature of the presence of rigid to flexible transitions in this archetypal glass. Consequences for window glass are discussed under this perspective.
The Structure of Silicate Glasses and Melts
Glasses and melts have unique physical and chemical properties, which vary as a function of temperature, pressure, and chemical composition. Understanding these properties requires an accurate structural description. The amorphous nature and complex chemical composition of glasses and melts do not allow the construction of a unique, crystal-like structural model. Nevertheless, despite the lack of periodicity and long-range order, glasses and melts retain a characteristic short-range order, which obeys basic crystal-chemical rules. However, only a limited amount of information exists about changes in a glass structure with temperature or pressure or both. Obtaining this information requires a combination of experimental and theoretical approaches. The connections between structural observations and melt properties are less well known, even at the qualitative level, although progress has been and continues to be made. Melt structure, properties, and dynamics were reviewed a decade ago and are discussed in detail in a recent book (Mysen and Richet 2005); we provide here only a few examples.
Effect of Sodium Oxide Modifier on Structural and Elastic Properties of Silicate Glass
The Journal of Physical Chemistry B, 2016
Molecular dynamics (MD) simulations and Brillouin Light Scattering (BLS) spectroscopy experiments have been carried to study the structure of sodium silicate glasses (SiO 2) (100-X) (Na O) X where X ranges from 0 to 45 at room temperature. The MD-obtained glass structures have been subjected to energy-minimization at zero temperature to extract the elastic constants also found by BLS spectroscopy. The found structures are in good agreement with the structural experimental data realized by different techniques. The simulations show that the values of the elastic constants as function of X Na 2 O mol% agree well with those measured by (BLS) spectroscopy. The variations of the elastic constants C11 and C44 as a function of the Na 2 O mol% are discussed and correlated to structural results and potential energies of oxygen atoms.
Annealing effects in SiO2–Na2O glasses investigated by Brillouin scattering
Journal of Non-Crystalline Solids, 2001
The elastic energy due to residual stresses in non-annealed SiO 2 ±Na 2 O glasses is determined in the frame of the theory of elasticity, assuming that a non-annealed glass can be considered as a distorted material in comparison with the annealed glass. An analysis of the elastic energy which is released at annealing is presented. Using hypotheses concerning the localisation of this energy in the glass and structural relaxation at annealing has allowed us to recalculate values of cation vibrational mode frequencies measured by infrared spectroscopy. The annealing eects on mechanical properties are studied and analysed in terms of glass structure, including phase separation at low sodium concentration. Ó
Structure and properties of sodium aluminosilicate glasses from molecular dynamics simulations The Journal of Chemical Physics 139, 044507 (2013); https://doi.org/10.1063/1.4816378 The structure of sodium silicate glass The Journal of Chemical Physics 93, 8180 (1990); https://doi.org/10.1063/1.459296 Cooling rate effects in sodium silicate glasses: Bridging the gap between molecular dynamics simulations and experiments Ab initio molecular dynamics has been applied to construct seven sodium silicate glass models with Na 2 O concentration ranging from 0 to 50 mol. %. The structures of the simulated (Na 2 O) x (SiO 2) 1-x glasses are critically analyzed and validated by comparing with available experimental data. Because the initial seed model is based on a near-perfect continuous random network model for amorphous SiO 2 with periodic boundaries, the structures of these silicate glasses are highly reliable. The electronic structure, interatomic bonding, and the mechanical and optical properties of seven models are calculated using the first-principles density functional method. In particular, a single quantum mechanical metric, the total bond order density (TBOD), is used to characterize the internal cohesion of sodium silicate glass. This is a significant step beyond the traditional analysis of glasses based purely on the geometric parameters. The TBOD value is found to decrease with increasing Na content, indicating the destruction of silica network connectivity. The calculated mass density and refractive index increase with x are in good agreement with experiment. The elastic coefficients and bulk mechanical properties exhibit a nonlinear variation in the series and depend greatly on the internal bonding and cohesion of the glass. The calculated Poisson's ratio indicates that the glass becomes more ductile with the addition of Na 2 O. Our results indicate that sodium silicate glass tends to be unstable for x greater than 0.4 due to the total destruction of the SiO 2 network. Published by AIP Publishing.
Quantitative analysis of elastic moduli and structure of B2O3–SiO2 and Na2O–B2O3–SiO2 glasses
Physica B: Condensed Matter, 2003
The average cross-link density % n c ; number of network bonds per unit volume n b ; average stretching force constant % F and atomic ring size c have been calculated for the binary B 2 O 3 -SiO 2 and ternary Na 2 O-B 2 O 3 -SiO 2 glass systems. These data have been used to calculate the bond compression bulk modulus K bc and Poisson's ratio s cal for each glass sample. The variation of these parameters and the ratio K bc =K e with composition were discussed quantitatively in terms of the change in structure of the glass network. The result showed that the connectivity and hence the rigidity of the B 2 O 3 -SiO 2 glasses decreases with increasing B 2 O 3 concentration. Whereas increasing of Na 2 O modifier in Na 2 O-B 2 O 3 -SiO 2 glasses increase the cross-link density due to the transformation of three-fold-coordinated boron atoms into fourfold-coordinated ones. This in turn raises the resistance of the network to deformation and increases the observed density and elastic moduli of this glass system. Moreover, the theoretical elastic moduli have been obtained for each glass sample and compared with the corresponding experimental values. The results showed excellent agreement for the majority of the samples examined. r
Rigidity transitions in glasses driven by changes in network dimensionality and structural groupings
EPL (Europhysics Letters), 2014
The method of in situ high-pressure neutron diffraction is used to investigate the structure of B 2 O 3 glass on compression in the range from ambient to 17.5(5) GPa. The experimental results are supplemented by molecular dynamics simulations made using a newly developed aspherical ion model. The results tie together those obtained from other experimental techniques to reveal three densification regimes. In the first, BO 3 triangles are the predominant structural motifs as the pressure is increased from ambient to 6.3(5) GPa, but there is an alteration to the intermediate range order which is associated with the dissolution of boroxol rings. In the second, BO 4 motifs replace BO 3 triangles at pressures beyond 6.3 GPa and the dissolution of boroxol rings continues until it is completed at 11-14 GPa. In the third, the B-O coordination number continues to increase with pressure to give a predominantly tetrahedral glass, a process that is completed at a pressure in excess of 22.5 GPa. On recovery of the glass to ambient from a pressure of 8.2 GPa, triangular BO 3 motifs are recovered but, relative to the uncompressed material, there is a change to the intermediate range order. The comparison between experiment and simulation shows that the aspherical ion model is able to provide results of unprecedented accuracy at pressures up to at least 10 GPa.
Philosophical Magazine, 2005
Calcium silicate glasses xCaO À (1 À x)SiO 2 exhibit a threshold in Raman lineshapes which can be related, on the basis of Maxwell constraint counting, to the onset of network rigidity as the concentration of calcium oxide x is decreased. The present results are more deeply characterized by a size-increasing cluster approximation that allows to perform Maxwell mechanical constraint counting beyond the usual meanfield treatment. This permits to discuss under which structural conditions an elastic intermediate phase should be obtained in the future.