The martensitic phase transition in NiTi

Abstract

The technique of perturbed angular correlation of gamma rays (PAC) was applied to study the martensitic phase transition of a shape-memory-effect alloy Ni_49.9Ti_50.1 doped with¹¹¹In/Cd probe atoms. Spectra measured above and below the martensite starting temperature,M _s ≈ 340 K, exhibit quadrupole interactions of probes at cubic and noncubic lattice sites, consistent with the respective crystal structures. Unlike spectra measured belowM _s those measured above exhibit a large frequency distribution attributed to lattice displacement waves observed in diffraction studies. Analysis tentatively suggests that the waves are dynamic and not static. BelowM _s, at 290 K, a static quadrupole interaction was observed with coupling frequency ω₁=34 Mrad/s and asymmetry parameter η=0.18, increasing to ω₁=40.5 Mrad/s and η=0.34 at 77 K.