Ultrasonic and Raman Spectroscopic Studies on Low-Energy Excitation of Alkali Metal Borate Glasses

点击翻译按钮获取中文摘要

A glass exhibits an excess of low-energy phonon excitation (boson peak) over that of a crystal. One purpose of this project is to study the low-energy excitation by means of ultrasound and Raman spectroscopy. Another purpose of this project is to show that the fragility of a glass-forming liquid is related to the anharmonicity of the resulting glass. The glass studied is the binary system of lithium borate glasses.(1) The density, the linear expansion coefficient and the change in ultrasonic velocity with temperature were measured for lithium borate glasses, from which the Gruneisen constant representing the anharmonicity was determined ; (2) The Gruneisen constant was also evaluated by analyzing the boson peak of Raman scattering on the basis of a theory that the boson peak is caused by an anharmonic vibration of atomic groups present in the glass-forming cluster. (3) It was found that the two sets of Gruneisen constant were in close agreement. (4) The temperature range of the glass transition was determined by differential thermal analysis and the fragility was evaluated from Tg/ΔT, where Tg and ΔT are the onset temperature of glass transition and the temperature width of glass transition, respectively, (5) It was found that the dependence of the Gruneisen constant on the glass composition is in close agreement with the dependence of the fragility on the glass composition.(6) It was concluded then that the fragility and the anharmonicity are interrelated with one another.