Ab-initio Molecular Dynamic Study On The Structure Of Aluminosilicate Glass

Aluminosilicate glasses have good mechanical properties and high transparency,and are an important system in the industry.Although the current researches on aluminosilicates glasses are relatively numerous,their structural theory and property optimization still attracts our attention.For the past few years,the accuracy and efficiency of ab-initio calculations have been improved a lot,becoming an important method of studying materials.In this paper,based on ab-initio molecular dynamic simulations,we have investigated a series of components which can't be obtained from ordinary experiments on their structures,properties and glass forming abilities.We aims to seek for the relationship between compositions,structures and properties,dig for application potentials and provide useful information for developing new materials.In this paper,at first,AIMD is adopted to explore structural and electronic properties of multi-componant aluminoborosilicate glasses with SiO₂?Al₂O₃?B₂O₃?Na₂O?MgO.The statistical calculating results of the structural properties are in good agreement with that of HE-XRD and solid-state NMR experiments,which proves that the calculation model used in this paper is reasonable.Additionally,the heat treatment process has little effect on the bond length and coordination number of the glass,but a great influence on the bond angle distribution.All of Si and part of the Al are 4-coordinated,consisting of network skeleton.B mainly exists in 3-coordination.The addition of 3-coordinated B and alkali ions makes the system have a larger averaged ring size.The electronic properties shows the introduction of modifier oxides into the network reduces the band gap.Then,using the same calculation methods,13 components from the glass forming zone of Na₂O-Al₂O₃-SiO₂ ternary phase diagram were investigated on their structures and glass-forming abilities.The simulation has found that the compositions beyond glass forming zone can still form glass by quenching at an extremely fast cooling rate in ab-initio calculations(around 10¹² K/s¹0¹⁴ K/s).With the range of SiO₂ content increasing from 30%to 60%,when Al/Na ratio increases,the glass network becoms more coherent.Calculated Young's moduli shows that some of the components outside the glass forming zone have high mechanical strength and potential for application.The compositions inside glass forming zone have a large glass transition temperature T_g and proper melting temperture T_m,leading to a bigger reduced glass transition temperature T_rg=T_g/T_m,thus indicating better glass forming ability.The compositions beyond glass forming zone have a small T_g and large T_m,causing a smaller T_rg=T_g/T_m,thus indicating weaker glass forming ability.Besides,the energy decreasing rate of the compositions inside glass forming zone is lower than those beyond glass forming zone.This gives rise to a small tendency of crystallization.What's more,we have carried out melting experiments to prove that the crystallizad compositions after annealing can form stable glasses after quenching.Although this is only a theoretical simulation,the research and production of glass will be of great significance,if ultra-fast cooling rate can be achieved.