The development by machine learning of models predicting materials' properties usually requires the use of a large number of consistent data for training. However, quality experimental datasets are not always available or self-consistent. Here, as an alternative route, we combine machine learning with high-throughput molecular dynamics simulations to predict the Young's modulus of silicate glasses. We demonstrate that this combined approach offers excellent predictions over the entire compositional domain. By comparing the performance of select machine learning algorithms, we discuss the nature of the balance between accuracy, simplicity, and interpretability in machine learning.
Structure and properties of magnesium silicate and borate melts and glasses were investigated by using newly parameterized interaction potentials in molecular dynamics simulations and compared with those of calcium silicate and borate. The competition between the depolymerization of the silica network and the formation of new bonds with modifier ions leads to the enhancement of the elastic moduli with increasing modifier content in alkaline earth silicate glasses. Compared with calcium silicate, the higher elastic moduli of magnesium silicate result from a higher connectivity of the overall gl…
We use large-scale simulations to investigate the dynamic fracture of silica and sodium-silicate glasses under uniaxial tension. The stress-strain curves demonstrate that silica glass is brittle whereas the glasses rich in Na show pronounced ductility. A strong composition dependence is also seen in the crack velocity which is on the order of 1800 m/s for glasses with low Na concentration and decreases to 700 m/s if the concentration is high. We find that during the fracture of Na-rich glasses very irregular cavities as large as 3-4 nm form ahead of the crack front, indicating the presence of …
We use \textit{ab initio} molecular dynamics simulations to investigate the properties of the dry surface of pure silica and sodium silicate glasses. The surface layers are defined based on the atomic distributions along the direction ($z-$direction) perpendicular to the surfaces. We show that these surfaces have a higher concentration of dangling bonds as well as two-membered (2M) rings than the bulk samples. Increasing concentration of Na$_2$O reduces the proportion of structural defects. From the vibrational density of states, one concludes that 2M rings have a unique vibrational signature …
The original electronic structure of the Pb$^{2+}$ ion explains its particular structural role in crystalline phases and silicate glasses. After a description of the structural role of lead in crystalline phases (PbO, silicates), this chapter presents a summary of the main structural studies carried out on glasses from the SiO$_2$-PbO, SiO$_2$-PbO-R$_2$O (R: alkaline) and SiO$_2$-PbO-Al$_2$O$_3$ systems, using various spectroscopic and simulation techniques.
For small tension the response of a solid to an applied stress is given by Hooke's law. Outside this linear regime the relation between stress and strain is no longer universal and at present there is no satisfactory insight on how to connect for disordered materials the stress-strain relation to the microscopic properties of the system. Here we use atomistic computer simulations to establish this connection for the case of silicate glasses containing modifiers. By probing how in the highly non-linear regime the stress-strain curve depends on composition, we are able to identify the microscopi…
In this work, we use molecular dynamics simulations to study the enhancement of surface over bulk diffusion (surface enhanced diffusion) in (PbO)x(SiO2)1-x glasses. This work is motivated to better understand surface diffusion in glasses and its connection to fragility, and to enhance surface diffusion in silica and related glasses for greater thermodynamic stability during vapor-deposition. By adding PbO to silica, the fragility of glass increases continuously for 10% <= x <= 70% during experiments. The increase in fragility may correspond to an increase in surface enhanced diffusion, as frag…
Density is one of the most commonly measured or estimated materials properties, especially for glasses and melts that are of significant interest to many fields, including metallurgy, geology, materials science and sustainable cements. Here, two types of machine learning (ML) models (i.e., random forest (RF) and artificial neural network (ANN)) have been developed to predict the room-temperature density of glasses in the compositional space of CaO-MgO-Al2O3-SiO2-TiO2-FeO-Fe2O3-Na2O-K2O-MnO (CMASTFNKM), based on ~2100 data points mined from ~140 literature studies. The results show that the RF …
Oxide glasses are made of a network of glass former polyhedra, and modifiers which have a role in neutralizing the charge of the glass former polyhedra or depolymerize the glass network. The effect of the modifier content on the structure and properties of the glass are to some extent, well known. However, the effect of the type of modifiers on the clustering and the tendency to form a phase separation in the glass is not investigated in detail and still not fully understood until now. Here, we use molecular dynamics to investigate the effect of the modifier type on the structure and the clust…
Multiscale Experimental Evidence of a Transitory State in the HDA-LDA Transition in Alumino-sodo-silicate Glasses
Institut Lumière Matière UMR CNRS 5306, Université Claude Bernard Lyon 1, CNRS（里昂第一大学物质与光研究所）；Institute of Glass and Ceramics, Department of Materials Science and Engineering, Friedrich Alexander University Erlangen Nuremberg（埃尔朗根-纽伦堡弗里德里希·亚历山大大学玻璃与陶瓷研究所）
Using molecular dynamics simulations we investigate the dependence of the structural and vibrational properties of the surfaces of sodo-silicate glasses on the sodium content as well as the nature of the surface. Two types of glass surfaces are considered: A melt-formed surface (MS) in which a liquid with a free surface has been cooled down into the glass phase and a fracture surface (FS) obtained by tensile loading of a glass sample. We find that the MS is more abundant in Na and non-bridging oxygen atoms than the FS and the bulk glass, whereas the FS has higher concentration of structural de…
We compare the ability of various interaction potentials to predict the structural and mechanical properties of silica and sodium silicate glasses. While most structural quantities show a relatively mild dependence on the potential used, the mechanical properties such as the failure stress and strain as well as the elastic moduli depend very strongly on the potential, once finite size effects have been taken into account. We find that to avoid such finite size effects, samples of at least 75,000 atoms are needed. Finally we probe how the simulation ensemble influences the fracture properties o…
Nature and distribution of iron sites in a sodium silicate glass investigated by neutron diffraction and EPSR simulation
采用高分辨中子衍射和经验势结构精细化（EPSR）方法研究了NaFeSi 2 O 6（NFS）玻璃的短程和中程结构。大部分（~60%）的Fe是4-配位的（[4]Fe），仅对应于三价铁，Fe 3+，距离d[4] Fe 3 +-O=1.87 $\pm$ 0.01 π。这与通过玻璃化学计量预测的3D结构不同。大多数[4] Fe 3+位点的存在说明了与晶体NaFeSi 2 O 6的结构不同的玻璃结构，晶体NaFeSi 2 O 6仅含有八面体Fe 3+。玻璃结构的EPSR模拟表明，[4] Fe 3+随机分布在硅酸盐网络中，与硅酸盐四面体共角。大多数[4] Fe 3+位置的存在不同于相应晶相的结构，其仅包含八面体Fe 3+。[4] Fe 3+的网络形成行为，加上Na+离子作为电荷补偿剂的存在，是含铁玻璃的特殊物理性质的起源，例如随着铁浓度的增加，硅酸钠玻璃的弹性模量增加。我们的数据还提供了5配位Fe的直接证据，平均距离d[5]Fe-O=2.01 $\pm$ 0.01 Å。该第二Fe群体涉及Fe 2+和Fe 3+两者。5-配位的Fe原子倾向于通过主要共享边缘而分离。三价铁在NFS玻璃中的双重作用的直接结构证据为理解NFS玻璃的特殊性质提供了支持，例如磁性，光学，电子或热力学性质。
The similarity in atomic structure between liquids and glasses has stimulated a long-standing hypothesis that the nature of glasses may be more fluid like, rather than an apparent solid. In principle, the nature of glasses can be characterized by measuring the dynamic response of rheology to shear strain rate in the glass state. However, limited by the brittleness of glasses and current experimental techniques, the dynamic behaviors of glasses were mainly assessed in the supercooled liquid state or in the glass state within a narrow rate range. Therefore, the nature of glasses has not been wel…
It has long been thought that shear band (SB) formation in amorphous solids initiates from relatively 'soft' regions in the material in which large-scale non-affine deformations become localized. The test of this hypothesis requires an effective means of identifying 'soft' regions and their evolution as the material is deformed to varying degrees, where the metric of 'softness' must also account for the effect of temperature on local material stiffness. We show that the mean square atomic displacement on a caging timescale <u2>, the 'Debye-Waller factor', provides a useful method for estimatin…
Establishing the composition-structure-property relationships for amorphous materials is critical for many important natural and engineering processes, including the dissolution of highly complex volcanic glasses. In this investigation, we performed force field molecular dynamics (MD) simulations to generate detailed structural representations for ten natural CaO-MgO-Al2O3-SiO2-TiO2-FeO-Fe2O3-Na2O-K2O glasses with compositions ranging from rhyolitic to basaltic. Based on the resulting atomic structural representations at 300 K, we have calculated the partial radial distribution functions, near…
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 …
