The Snoek relaxation in bcc metals—From steel wire to meteorites

Heavy interstitial atoms, such as O, N, or C, when dissolved in bcc metals (Fe, Nb, Ta, V), induce elastic dipoles with tetragonal symmetry. The stress induced reorientation produces anelastic relaxation and is the elementary step of interstitial diffusion. Mechanical loss spectra indicate the presence of interstitial atoms by Snoek peaks at distinct, characteristic temperatures. The magnitude of the peaks is proportional to the concentration of interstitial atoms in solution. The atomic model and theory of the Snoek relaxation for ideal interstitial solutions are presented.