Experimental Measurement of Configurational and Vibrational Entropy in Metallic Glasses

Liquid fragility characterizes how quickly viscosity decreases above the glass transition in glass-forming liquids. This property is fundamental to glass physics and of critical importance for engineering applications. Competing theories have suggested that vibrational properties may play a role in describing fragility by contributing vibrational entropy to the large excess entropy of the undercooled liquid over the crystal above the glass transition [1]. We have developed in situ inelastic neutron scattering methods to assess the phonon density of states in glasses as they traverse the glass transition, capturing real-time changes to the phonon vibrational modes in the amorphous, crystalline, and supercooled liquid states. Results on bulk metallic glasses with a range of fragilities have been reported [2, 3], indicating that vibrational entropy provides a minor contribution to the entropy of the glass transition. This talk will discuss the correlation between excess vibrational entropy in the undercooled liquid and liquid fragility. These new results will be considered in the context of a universal understanding of vibrational contributions to the thermodynamics of the glass transition, and in comparison with additional glass systems.<br/> <br/>1. Martinez, L.-M. & Angell, C. A. Nature <b>410</b>, 663–667 (2001).<br/>2. Smith, H. L. et al., Nature Physics <b>13</b>, 900–905 (2017).<br/>3. Smith, H.L. et al., Materialia <b>27</b>, 101710 (2023).