A major challenge in the modeling of ionically conducting glasses is to understand how the large variety of possible chemical compositions and specific structural properties influence ionic transport quantities. Here we revisit and extend a theoretical approach for alkali borophosphate glasses, where changes of conductivity activation energies with the borate to phosphate mixing ratio are related to modifications of the ionic site energy landscape. The landscape modifications are caused by varying amounts of different units forming the glassy network, which lead to spatial redistributions of the counter-charges of the mobile alkali ions. Theoretical approaches are presented to calculate variations of both network former unit concentrations and activation energies with the glass composition. Applications to several alkali borophosphate glasses show good agreement with experimental data.
For ion transport in network glasses, it is a great challenge to predict conductivities specifically based on structural properties. To this end it is necessary to gain an understanding of the energy landscape where the thermally activated hopping motion of the ions takes place. For alkali borophosphate glasses, a statistical mechanical approach was suggested to predict essential characteristics of the distribution of energies at the residence sites of the mobile alkali ions. The corresponding distribution of site energies was derived from the chemical units forming the glassy network. A hoppi…
A new theoretical approach is presented for relating structural information to transport properties in ion conducting network glasses. It relies on the consideration of the different types of glass forming units and the charges associated with them. Changes in the compositions of these units lead to a re-distribution of Coulomb traps for the mobile ions and to a subsequent change in long-range ionic mobilities. It is furthermore shown how measured changes of the unit compositions can be explained by thermodynamic modeling. The theories are tested against experiments on borophosphate glasses an…
We apply a recently developed optimization scheme to obtain effective potentials for alkali and alkaline-earth aluminosilicate glasses that contains lithium, sodium, potassium, or calcium as modifiers. As input data for the optimization, we used the radial distribution functions of the liquid at high temperature generated by means of ab initio molecular dynamics simulations and density and elastic modulus of glass at room temperature from experiments. The new interaction potentials are able to reproduce reliably the structure and various mechanical and vibrational properties over a wide range …
Although it is indeed commonly believed that, as frozen supercooled liquids, glasses should continue to flow over the years (e.g., in the case of the stained-glass windows of medieval cathedrals), the dramatic increase of their viscosity below the glass transition temperature suggests, on the contrary, that their relaxation time is on the order of 10$^{32}$ years at room temperature. However, a recent study conducted by Mauro et al. reported the intriguing dynamics of the relaxation of a commercial Corning Gorilla Glass at room temperature, over 1.5 years. Here, we report a novel atomistic sim…
A new class of Erbium doped glasses with compositions xNa2O - (60-x)PbCl2 - 40P2O5 (x=0, 10, 20 and 30) were fabricated and characterized for optical properties. Absorption spectra were analyzed for important Judd-Ofelt parameters from the integrated intensities of various Er3+ glass absorption bands. Photoluminescence (PL) and its decay behavior studies were carried out for the transition 4I13/2 -> 4I15/2. A systematic correlation between the Judd-Ofelt parameter {omega}2 and the covalent nature of the glass matrix was observed, due to increased role of bridging oxygens in the glass network. …
In this communication we report the fluorine ion dynamics in mixed alkali oxyfluro vanadate glasses. We have measured the electrical conductivity using impedance spectroscopy technique Room temperature conductivity falls to 5 orders of magnitude from its single alkali values at 33 mol% of rubidium concentration. We have also estimated the distance between similar mobile ions using the density values. Assuming this distance as the hopping distance between the similar ions we have estimated the anionic (Fluorine ion in our case) conductivity. It is observed that the fluorine ion dynamics mimics …
We analyze the dependence of relative proportion of various characteristic clusters in binary alcali-borate glasses on modifier's concentration $x$. A pure $B_2O_3$ glass contains a huge amount of boroxol rings and some amount of boron atoms in between, linking the boroxol rings via oxygen bonds. The addition of the $Na_2O$ modifier creates four-coordinated borons, but the resulting network glass remains totally connected. We study local transformations that lead to creation of new configurations like tetraborates, pentaborates, diborates, etc., and set forth a non-linear differential system s…
The mixed-alkali effect on the cation dynamics in silicate glasses is analyzed via molecular dynamics simulations. Observations suggest a description of the dynamics in terms of stable sites mostly specific to one ionic species. As main contributions to the mixed--alkali slowdown longer residence times and an increased probability of correlated backjumps are identified. The slowdown is related to the limited accessibility of foreign sites. The mismatch experienced in a foreign site is stronger and more retarding for the larger ions, the smaller ions can be temporarily accommodated. Also correl…
Peculiarities of mixed cation effect in ternary glasses whose composition involves alkali and non-alkali unicharged ions and/or alkaline earth ions are explored within context of defect model for mixed mobile ion effect (V. Belostotsky, J. Non-Cryst. Solids (2007)). In mixed alkaline earth glasses mixed cation effect is observed as in ionic diffusivity as well as in the glass transition temperature reflecting the fact that movement of dissimilar ions of unequal size is accompanied by formation of intrinsic defects in glass matrix when mobile ions enter foreign sites. It is qualitatively simila…
Based on a hopping model we show how the mixed alkali effect in glasses can be understood if only a small fraction c_V ofthe available sites for the mobile ions is vacant. In particular, we reproduce the peculiar behavior of the internal friction and the steep fall (''vulnerability'') of the mobility of the majority ion upon small replacements by the minority ion. The single and mixed alkali internal friction peaks are caused by ion-vacancy and ion-ion exchange processes. If c_V is small, they can become comparable in height even at small mixing ratios. The large vulnerability is explained by …
Applying coherent X-rays by the method of atomic-scale X-ray Photon Correlation Spectroscopy results in beam-induced dynamics in a number of oxide glasses. Here these studies are extended to rubidium and caesium borates with varying alkali contents. While no cumulative beam damage is observed, the observed rate of structural rearrangements shows a linear relation to the dose rate. In agreement with the increasing glass transition temperature, the rate of dynamics at given dose rate decreases with increasing alkali content, while the shape of the decay of correlations becomes progressively stre…
Ion conducting $(CaO)_x(SiO_2)_{1-x}$ glasses and melts show a threshold behaviour in dc conductivity near $x=x_t=0.50$, with conductivities increasing linearly at $x>x_t$. We show that the behaviour can be traced to a rigid ($x<0.50$) to floppy ($x>0.50$) elastic phase transition near $x=x_t$. In the floppy phase, conductivity enhancement is traced to increased mobility or diffusion of $Ca^{2+}$ carriers as the modified network elastically softens.
We explore progress in understanding the behaviour of cation conducting glasses, within the context of an evolving ''dynamic structure model'' (DSM). This behaviour includes: in single cation glasses a strong dependence of ion mobility on concentration, and in mixed cation glasses a range of anomalies known collectively as the mixed alkali effect. We argue that this rich phenomenology arises from the emergence during cooling of a well-defined structure in glass melts resulting from the interplay of chemical interactions and thermally driven ionic motions. The new DSM proposes the existence of …
Rare-earth (RE) containing alkali aluminoborosilicate glasses find increasingly broad technological applications, with their further development only impeded by yet-poor understanding of coordination environment and structural role of RE ions in glasses. In this work we combine free induction decay (FID)-detected electron paramagnetic resonance (EPR), electron spin echo envelope modulation (ESEEM), and MAS NMR spectroscopies, to examine the coordination environment and the clustering tendencies of RE3+ in a series of peralkaline aluminoborosilicate glasses co-doped with Nd2O3 (0.001-0.1 mol%) …
Individual cationic site--energies are explicitly determined from molecular dynamics simulations of alkali silicate glasses, and the properties and relevance of this local energetics to ion transport are studied. The absence of relaxations on the timescale of ion transport proves the validity of a static description of the energy landscape, as it is generally used in hopping models. The Coulomb interaction among the cations turns out essential to obtain an average energy landscape in agreement with typical simplified hopping models. Strong correlations exist both between neighboring sites and …
In recent years, tailoring the properties of bioactive glasses through compositional design have become the subject of widespread interest for their use in medical application, e.g., tissue regeneration. Understanding the mixed alkali effect (MAE) in oxide glasses is of fundamental importance for tailoring the glass compositions to control the mobility of ions and, therefore, the glass properties that depend on it, such as ion release, glass transition temperature, and ionic conductivity. However, most of the previously designed bioactive glasses were based on trial-and-error, which is due to …
Electrical modulus analysis of the frequency dependent conductivity data over the range from 100 Hz to 10 MHz and at temperature range of 140 oC to 300 oC were carried out on the mixed alkali vanadate glass samples having lithium and rubidium as alkali elements. The analysis of the data is done using Kohlrausch-Williams-Watts (KWW) equation which describes the relaxation behavior of the mobile species. We have used the Bergman equation (R. Bergman, J. Apl. Phys. 88 (2000) 1356.) for fitting the imaginary part of the electrical modulus. The stretching parameter beta derived from this fit shows …
The question of whether glass continues to relax at low temperature is of fundamental and practical interest. Here, we report a novel atomistic simulation method allowing us to directly access the long-term dynamics of glass relaxation at room temperature. We find that the potential energy relaxation follows a stretched exponential decay, with a stretching exponent $β= 3/5$, as predicted by Phillips' diffusion-trap model. Interestingly, volume relaxation is also found. However, it is not correlated to the energy relaxation, but is rather a manifestation of the mixed alkali effect.
The powdery nature and high alkali content of vegetable ashes make them ideal raw materials to be used as modifiers of silicate compositions (glasses, enamels and ceramics). Their utilisation since ancient times is described in the literature of the history of glasses, but studies on the analyses of their composition are still limited. We discuss here the compositions of tree and shrub ashes (wattle, hawthorn, oak, green oak, olive wood, elm, poplar, apple tree, vine shoot), of plants (carex, fern, dogwood), of cereals (wheat, maize, rice), threshing waste and hay, mainly harvested in Maconnai…
Physics-Informed Symbolic Regression for Predicting the Glass Transition Temperature of Alkali Borate Glasses
Federal University of Sergipe（塞尔希培联邦大学）；Federal University of Lavras (UFLA)（拉夫拉斯联邦大学）；Federal University of Bahia（巴伊亚联邦大学）；Brazilian Center for Research in Energy and Materials (CNPEM)（巴西能源与材料研究中心）
We adapt and apply a recently developed optimization scheme used to obtain effective potentials for aluminosilicate glasses to include the network former boron into the interaction parameter set. As input data for the optimization, we used the radial distribution functions of the liquid at high temperature generated by ab initio molecular dynamics simulations, and density, coordination and elastic modulus of glass at room temperature from experiments. The new interaction potentials are shown to reproduce reliably the structure, coordination and mechanical properties over a wide range of compos…
The powdery nature and high alkali content of vegetable ashes make them ideal raw materials to be used as modifiers of silicate compositions (glasses, enamels and ceramics). Their utilisation since ancient times is described in the literature of the history of glasses, but studies on the analyses of their composition are still limited. We discuss here the compositions of tree and shrub ashes (wattle, hawthorn, oak, green oak, olive wood, elm, poplar, apple tree, vine shoot), of plants (carex, fern, dogwood), of cereals (wheat, maize, rice), threshing waste and hay, mainly harvested in Maconnai…
The energies of the alkali exchange reactions are computed from density functional calculations for a series of alkali silicate minerals. First-principles calculations are compared against (1) experiment; (2) thermodynamic models; (3) calculations using empirical interatomic potentials (with both polarizable shell model potentials and pairwise potentials with partial charges); and (4) empirical correlations based on optical basicity and Pauling bond strength. The first-principles calculations correlate well with experimental values. The shell model potentials appear to account for Si-O-Si vers…
The frequency and temperature dependence of the dielectric constant, electric modulus and electrical conductivity of the transparent glasses in the composition 0.5Li2O-0.5Na2O-2B2O3 (LNBO) were investigated in the 100 Hz - 10 MHz frequency range. The dielectric data have been analyzed using Cole-Cole equation with an addition of the conductivity term. The electrical conductivity was found to be obeying Jonscher's universal law. The dielectric constant and the loss for the as-quenched glasses increased with increasing temperature, exhibiting anomalies in the vicinity of the glass transition and…
