Glass: Kohlrausch exponent, fragility, anharmonicity

Area of Science:

• Materials Science
• Thermodynamics
• Condensed Matter Physics

Background:

• Glass exhibits complex thermodynamical and mechanical properties governed by relaxation dynamics.
• Understanding the behavior of fragile and strong glasses is crucial for materials science applications.

Purpose of the Study:

• To model the thermodynamical and mechanical properties of glasses using a generalized activation energy relationship.
• To establish consistency relationships for glass relaxation phenomena and explore correlations between various parameters.

Main Methods:

• Modeling glass-forming liquids based on a generalized activation energy relationship (modified VFT law).
• Calculating relaxation of properties (volume, enthalpy, stress, creep) approximated by the Kohlrausch function.
• Analyzing consistency relationships for Kohlrausch exponent, stabilization time, and activation parameters.

Main Results:

• The model predicts consistency relationships for temperature/aging time variation of the Kohlrausch exponent and stabilization time domains.
• Lawson and Keyes (LK) relations are observed generally in glass, with macroscopic and microscopic ratios equaling κγ.
• Grüneisen parameter (γ(B)) and Mean Square Displacement (MSD) are identified as key parameters governing glass relaxation properties.

Conclusions:

• The Grüneisen parameter and MSD characterize anharmonicity and govern glass relaxation.
• Linear relations between γ(B), fragility (m), and Kohlrausch exponent (n(g)) are explained.
• Glass former fragility strongly correlates with the extent of anharmonicity in interatomic interactions.