Secondary Relaxation in Metallic Glass Formers: Its Correlation with the Genuine Johari−Goldstein Relaxation

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 La 55 Al 25 Ni 20 metallic glasses. The observed β relaxation exhibits a typical feature of the genuine JG relaxation, i.e., the variation of its activation energy ( E β ) with the glass transition temperature ( T g ) obeys the relation E β = 26.8 RT g . The correlative degree between the β and the primary α relaxations is closely associated with the liquid fragility. By a survey of the sub- T g relaxation data of other metallic glass systems, we have determined the E β values that find the correlation E β = 26.1 RT g, indicating that JG relaxations are intrinsic in metallic glass formers. By analyzing the primitive relaxation time of the JG motion, τ 0,JG, and the crossover time in the Coupling model, t c, we discuss why the excess wing rather than the JG peak (or shoulder) is present in metallic glass systems.