Distinctive slow β relaxation and structural heterogeneity in (LaCe)-based metallic glass

The (LaCe)_32.5Co₂₀Al₁₅ bulk metallic glass was found to display a pronounced slow β-relaxation at low temperature, which was well separated by α-relaxation based on the mechanical spectroscopy. The activation energy for α-relaxation E_α is 335 kJ/mol, and this process revealed in the master curve can be well fitted by a Kohlrausch-Williams-Watts (KWW) function with γ_KWW value of 0.463. The activation energy for the slow β-relaxation E_β is determined to be 76 kJ/mol, which obeys an empirical rule that E_β equals 22RT_g. The dynamic mechanical behavior of this metallic glass can be well explained by quasi-point defects (QPDs) theory. The correlation factor χ is deduced to be 0.44 from the experimental results, which suggests remarkable heterogeneity in this (LaCe)-based metallic glass. This closely relates to the origin of the prominent slow β-relaxation.