Strain glass in doped Ti₅₀(Ni_50-xD _x) (D = Co, Cr, Mn) alloys: Implication for the generality of strain glass in defect-containing ferroelastic systems

Strain glass is a new glassy state discovered recently in Ni-rich Ti-Ni ferroelastic alloys. However, it remains unclear whether or not strain glass can be found in a wide range of ferroelastic systems. Here, we investigated the transition behavior of three different defect-doped systems Ti ₅₀(Ni_50-xD_x) (D = Co, Cr, Mn) and found a striking similarity in their transition behavior as a function of defect concentration x. In all these systems, there exists a critical doping level x_c at which the transition behavior shows an interesting crossover. At x < x_c, these materials undergo a martensitic transition and the transition temperature decreases with increasing x. However, at x > x_c, the martensitic transition is suppressed and a strain glass transition occurs. These results imply that strain glass may be quite general in defect-containing ferroelastic systems. An analysis with a modified Landau-type free energy landscape suggests that although point defects always favor the formation of strain glass, to actually form a strain glass they need to destabilize the martensite of the system.