What controls temperature dependence of yield stress in L1₂-ordered intermetallic compounds?

The temperature dependence of yield stress and the associated dislocation dissociation in Ll₂ intermetallic compounds are investigated in order to check the feasibility of the classification of Ll₂ intermetallic compounds so far made in terms of the planarity of core structures of partial dislocations with b = 1/2<110> and 1/3<112> on {111} and {001} glide planes. In contrast to what is believed from the classification, the motion of APB-coupled dislocations is evidenced to give rise to the rapid decrease in yield stress at low temperatures for Pt₃Al. In view of the fact that rapid decrease in yield stress at low temperatures is also observed in Co₃(Al,W) and C0₃Ti in which APB-coupled dislocations are responsible for deformation, the SISF-type dissociation is not a prerequisite for the rapidly decreasing CRSS for slip on (111) and the relative magnitudes of the APB energy on (111) and the SISF energy on (111) cannot be a primary factor that determines the type of the temperature dependence of CRSS for Ll₂ compounds. The importance of the CSF energy as a factor determining the type of the temperature dependence of yield stress for Ll₂ compounds through the changes in the planarity of the core structure of the APB-coupled partial dislocation with b_p =1/2[110]is discussed in the light of experimental evidence obtained from Pt₃Al.