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

玻璃表现出比晶体更多的低能声子激发(玻色子峰)。本项目的目的之一是利用超声和拉曼光谱来研究低能激发。这个项目的另一个目的是证明玻璃形成液体的易碎性与产生的玻璃的非谐性有关。(1)测量了硼酸锂玻璃的密度、线膨胀系数和声速随温度的变化，由此确定了代表非谐性的Gruneisen常数；(2)根据玻色子峰是由玻璃形成团簇中原子基团的非简谐振动引起的理论，通过分析拉曼散射的玻色子峰，计算了Gruneisen常数。(3)两组Gruneisen常数基本一致。(4)通过差热分析确定了玻璃化转变的温度范围，并用TG/ΔT评价了玻璃化转变的脆性，其中Tg和ΔT分别是玻璃化转变的起始温度和玻璃化转变的温度宽度。(5)发现玻璃组成与玻璃组成的关系与玻璃的脆性关系是一致的。

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.