Impact of delocalized nonlinear vibrational modes on the properties of NiTi

The behavior of twenty-five one-component three-dimensional DNVMs in the simple cubic titanium and nickel sublattices, and their influence on binary NiTi alloy properties, are studied using molecular dynamics simulations. Seventeen DNVMs exhibit stable time-periodic vibrations, while the remaining eight DNVMs are unstable. These unstable modes transfer vibrational energy between sublattices upon excitation. Most stable DNVMs exhibit a hard-type nonlinearity, where the frequency increases with increasing amplitude. Stable DNVMs can accumulate energy in the range of 0.1–1.0 eV per atom for both the nickel and titanium sublattices. The specific heat decreases (increases) for DNVMs with a hard (soft) type of nonlinearity. Excitation of DNVMs results in positive compressive stresses proportional to the displacement vector length. These results provide insight into the complex behavior of DNVMs in a binary NiTi alloy and their impact on material properties.