Motion of oxygen in vanadium and niobium studied by nuclear magnetic resonance

The motion of oxygen in solid vanadium and niobium, containing different amounts of oxygen (0.26-3.40at%), was studied by means of 51-V and 93-Nb nuclear spin relaxation (NSR) measurements at 300K<T<1400K. In the entire temperature range the Zeeman NSR rate 1/T1 is determined by fluctuations of the conduction electron-nucleus-interaction. The rotating frame NSR rates 1/T1r, however, exhibit three distinct maxima at elevated temperatures, in addition to the conduction electron induced contribution. These NSR peaks are shown to be caused by fluctuations of the nuclear quadrupole interaction of the probe nuclei due to migration of interstitial oxygen atoms. From the experimental data the corresponding activation energies Ea and pre-exponential factors ford respective oxygen jump rates have been determined. We found that the activation energies of the atomic jump rates are nearly identical for all three relaxation mechanisms (about 1eV). the results are discussed in the framework of three existing models for the diffusion of interstitial impurities in metals