Structure Origin Of Evolution Of Mechanical Properties For Phosphosilicate Glasses

Because of rich resources and environmental friendly,and also the low glass transition temperature,range larger thermal expansion coefficient and low viscosity,Phosphosilicate glasses has been widely concerned.Phosphosilicate glasses have various potential applications and have been known for their complex physical properties and atomic structure depending on composition.Application of phosphosilicate glasses is mainly focused on silica-rich compositions.Such glasses have recently gained importance in medical applications,advantages of these materials are their biological activity.From phosphosilicate compositions rich in phosphorous,one can obtain homogeneous glasses.Such as laser componentand light emitting materials.Furthermore,phosphorous-rich compositions glasses are interesting from a structural point of view,as they exhibit abundant structural,including six-fold coordinated silicon.In this paper,the components of 0.3MO·0.7[ySiO₂·?1-y?P₂O₅]?M is one or more of Mg,Ca,Sr,Ba?were studied.The glasses were prepared by quenching-milling method.The properties under study include vickers indentation hardness,density???,the glass transition temperature,liquid fragility index and the chemical stability for a series of phosphosilicate glasses.and the structural changes of the glasses were investigated by nuclear magnetic resonance and Raman spectroscopy.The structural origin of evolution of performances for physical properties in the effects of six-fold coordinated silicon was discussed.On the other hand,topological constraint theory as applied to phosphosilicate glasses that can quantitatively predict glass properties in the effects of six-fold coordinated silicon.At the end of the paper,correlation between the six-fold coordinated silicon and optical basicity were studied.The primary contents and results are as follows:?1?Along with the increase of SiO₂,the percentage of Si^?6?in network former units?NFUs?increases first and then decreases,with the maximum percentage occurring at13 mol%of SiO2.?2?It was found that the HV,density and Tg of glasses do not always in a linear change with adding the content of SiO₂ and there exist maximum hardness?6.63MPa?,density?3.352g/cm³?and minimum Tg?807.9K?at a certain content of SiO₂,which was found to be mainly related to the constraints originated from six-fold coordinated silicon network former units.?3?Along with the increase of alkaline earth metal ionic radius,the chemical stability of MO-SiO₂-P₂O₅ glasses increase.When the content of SiO₂ is add,the chemical stability of BaO-SiO₂-P₂O₅ glasses drops slowly.When the alkali metal or alkaline earth metal oxide partly replace barium oxide,the chemical stability is worse than BaO-SiO₂-P₂O₅ glasses.?4?The observed compositional trend is well reproduced by the model without any adjustable fitting parameters.But the model Tg is little overestimating from the test Tg It was assumed that the potential energy barrier to viscous flow does not change with composition.This is a reasonable approximation within a family of glasses,but may be problematic in a mixed-network former glass.?5?Phosphosilicate glasses can produce Si^?6?when optical basicity between 0.35with 0.48.The Si^?6?/[Si^?6?+Si^?4?]ratio of phosphosilicate glasses become maximum value when optical basicity between 0.38 with 0.42.However,the Si^?6?/[Si^?6?+Si^?4?]ratio differ from each other.This largely depends on the network modifier in glasses.