Analysis of Non-Gaussian Parameter on Metallic Glass-Forming Cu-Ti-Zr Melts

To explore the mechanism behind slow dynamics of the glass transition is an interesting topic from a statistical physical point of view [1, 2]. One of characteristic dynamical properties in glass-forming systems is described by a non-Gaussian parameter α2(t) [3], which is related to the mean-square and –fourth displacements, M2(t) and M4(t), through the relation α2(t)=3M4(t)/5M2(t)-1. It has a single peak as a function of time t and the peak value is almost zero in liquid region. However, the peak value becomes higher and the peak time tNGP becomes longer for lower temperatures. Although many extensive simulation studies for α2(t) have been made [4], theoretical understanding is still incomplete. In this paper, we investigate α2(t) by performing molecular dynamics simulations on ternary metallic glass-forming Cu60Ti40-xZrx for different compositions, x=10, 20, 30 [5]. The analysis is based on the mean-field theory (MFT) proposed by one of the author (MT) [6]. MFT suggests that the self-diffusion coefficient DS could be a universal parameter, which can characterize the dynamics of a single atom. This is also tested for α2(t). We show that the peak time tNGP is described by DS only (see Fig. 1). Hence, a length scale ξ of the peak is given by ξ=(tNGPDS) and is compared with a cage length l of M2(t) in Fig. 2. This is larger than l and becomes smaller for larger u. By considering that ξ represents a cage length of M4(t), one can express the peak value of α2(t) in terms of ξ and l. The details will be given in the poster session.