Borate anomaly, anharmonicity and fragility in lithium borate glasses

Author： Kodama M. Kojima S. Feller S. Affatigato M.

ISSN： 0031-9090

Source： Physics and Chemistry of Glasses - European Journal of Glass Science and Technology Part B, Vol.46, Iss.2, 2005-04, pp. : 190-193

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Abstract

The occurrence of minima in the thermal expansion coefficients of alkali borate glasses is considered anomalous in the literature and the behaviour is termed the borate anomaly. The borate anomaly relates essentially to anharmonic vibrational properties. In order to study the vibrational anharmonicity in lithium borate glasses xLi₂O–(1–x)B₂O₃ (0≤x≤0·28), the density, the linear expansion coefficient, the longitudinal and transverse ultrasonic velocities and their respective temperature coefficients of the velocities have been measured. From these physical quantities, the Anderson–Grüneisen constants representing vibrational anharmonicity are calculated. These constants all show minima at x≈0·08. For a glass forming liquid, the dependence of viscosity on temperature is often expressed in terms of fragility. The fragility of lithium borates is evaluated from the temperature width of the glass transition. Fragility also shows a minimum at x≈0·08. We show that the constants representing anharmonicity strongly correlate with the fragility.