Mechanism of Unique Structural Relaxation of Optical Functional Oxide Glasses with Low Phonon Energy

The purpose of this study is to clarify the mechanism of unique structural relaxation of optical functional TeO I D22文件D2-and Bi I D22文件D2O文件D23文件D2-based glasses with low phonon energies through measurements of viscosity，heat capacity and Vickers hardness in the glass transition region。The following results were obtained.1 the thermal stability against crystallization in R I D22个D20-MO-TeO D22个D2glasses(R=Li，Na，K，M=Mg，Ba，Zn)increases with the combination between oxides showing large different optical basicities(e.g.K I D22个D2O-MgO，Li D22个D20-BaO).2)the heat capacity changes at glass transin K D 22个20-20-O-MgO，2)the heat capacity changes at the glass transin K-D 22-20-20-O-D-2J/2J/D2J/D20-D。2)the heat capacity changes at the glass transined.1。Meaning that the breaking of the network structure and rearrangements among network units occur easily in these glasses.This feature is appeared in a rapid decrease of Vickers hardness at the glass transition.3)the activation energies for enthalpy relaxation in TeO ei D22文件D2-based glasses are900~1250kJ/mo，which are much large compared with silicate glasses，and those for viscous flow are 500~750kJ/mol，giving the fragility values of around 60。The decoupling between enthalpy relaxation and viscous flow is clearly observed in both TeO I D22文件D2-and Bi I D22文件D2O文件D23文件D2-based(such as Bi I D22文件D20文件D23文件D2-B文件D22文件D2)glasses.4)both TeO文件D22文件D2-and Bi D 22文件D2-based glasses belong to catthe egory of fragile glass-forming systems semaxation，the decoupling between enthalpy relaxation and viscous flow is clearly observed in both Tey D2-B I D22文件D2-based glasses belong to catthe egory of fragile glass-forming systems.But the present study demonstrates that it is possible to fabricate glasses having high potential for technical applications.

The purpose of this study is to clarify the mechanism of unique structural relaxation of optical functional TeOィイD22ィエD2- and BiィイD22ィエD2OィイD23ィエD2-based glasses with low phonon energies through measurements of viscosity, heat capacity and Vickers hardness in the glass transition region. The following results were obtained.1) the thermal stability against crystallization in RィイD22ィエD20-MO-TeOィイD22ィエD2 glasses (R=Li,Na, K, M=Mg, Ba, Zn) increases with the combination between oxides showing large different optical basicities ( e.g. KィイD22ィエD2O-MgO, LiィイD22ィエD20-BaO).2) the heat capacity changes at the glass transition in KィイD22ィエD20-MgO-TeOィイD22ィエD2 glasses are extremely large, I.e. ΔCィイD2PィエD2A=45J/molK, meaning that the breaking of the network structure and rearrangements among network units occur easily in these glasses. This feature is appeared in a rapid decrease of Vickers hardness at the glass transition.3) the activation energies for enthalpy relaxation in TeOィイD22ィエD2-based glasses are 900〜1250kJ/mo, which are much large compared with silicate glasses, and those for viscous flow are 500〜750kJ/mol, giving the fragility values of around 60. The decoupling between enthalpy relaxation and viscous flow is clearly observed in both TeOィイD22ィエD2- and BiィイD22ィエD2OィイD23ィエD2-based (such as BiィイD22ィエD20ィイD23ィエD2-BィイD22ィエD20ィイD23ィエD2) glasses.4) both TeOィイD22ィエD2- and BiィイD22ィエD2OィイD23ィエD2-based glasses belong to the category of fragile glass-forming systems.5) both systems show a unique structural relaxation at the glass transition, but the present study demonstrates that it is possible to fabricate glasses having high potential for technical applications.