Abstract
We report experimental evidence for the existence of Johari−Goldstein (JG) relaxation in metallic glass formers. By using the hyperquenching−annealing−calorimetric approach, we study the dynamics of the secondary (β) relaxation in La55Al25Ni20 metallic glasses. The observed β relaxation exhibits a typical feature of the genuine JG relaxation, i.e., the variation of its activation energy (Eβ) with the glass transition temperature (Tg) obeys the relation Eβ = 26.8RTg. The correlative degree between the β and the primary α relaxations is closely associated with the liquid fragility. By a survey of the sub-Tg relaxation data of other metallic glass systems, we have determined the Eβ values that find the correlation Eβ = 26.1RTg, indicating that JG relaxations are intrinsic in metallic glass formers. By analyzing the primitive relaxation time of the JG motion, τ0,JG, and the crossover time in the Coupling model, tc, we discuss why the excess wing rather than the JG peak (or shoulder) is present in metallic glass systems.
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