A Model for the Fragility of Metallic Glass Forming Liquids

Abstract

An expression for the temperature dependence of the viscosity and fragility is derived based on a simple model of the melt. According to the model, the fragility is determined by the relaxation of structural units that form the melt, and is described in terms of the bond strength, coordination number, and their fluctuations of the structural units. It is shown that the fragility of some metallic glass forming liquids such as Pd 40 Ni 40 P 20 , La 55 Al 25 Ni 20 and Zr 65 Al 10 Ni 10 Cu 15 are quite well reproduced by the model. The application of the theory to La 55 Al 25 Ni 20 has revealed that the fluctuation in the bond strength between the structural units is about 6% and that the viscous flow occurs when the bonds in about 8 adjoining structural units are broken.

Bond strength-coordination number fluctuations and the fragility of some ion-conducting oxide and chalcogenide glass-forming liquids

“…3. For the sake of comparison, the values of other systems determined previously are also shown [7,8,15]. We can see clearly that strong systems are characterized by large bond strength C and small fluctuations B, whereas fragile systems are characterized by small bond strength and large fluctuations.…”

“…On the other hand, fragile system such as ZBLA (ZrF 4 -BaF 2 -LaF 3 -AlF 3 ) has a small value of C and a large value of B. Metallic and semiconducting chalcogenide systems exhibit intermediate behavior [7,8].…”

A comparative study of the viscosity of ion conducting polymers based on the bond strength-coordination number fluctuation model and other models

“…For instance, it has been shown previously that large value of C and small value of B correspond to strong systems, whereas small value of C and large value of B correspond to fragile systems [11]. From Fig.…”

“…3, we can learn that a high value of the total bond strength between the structural units C and a low value of its fluctuation B results in a less fragile system [11]. The Vogel-Fulcher-Tamman equation…”

Correlation between fragility and cooperativity in bulk metallic glass-forming liquids

“…Therefore, it is expected that by using the BSCNF model, further insights on the viscous flow can be extracted which have not been revealed in the analysis by the VFT equation. On this regard, we have already shown that, a quantity N B , which is defined from the BSCNF model [14], gives the number of structural units involved in the thermally activated viscous flow. It has been also shown that N B can be expressed analytically with the BSCNF model parameters [15], and is closely related with the well-known concept of ''cooperatively rearranging region (CRR)'' in the theory of Adam and Gibbs [16].…”