MOTION OF OXYGEN IN VANADIUM AND NIOBIUM STUDIED BY NUCLEAR-MAGNETIC-RESONANCE

The motion of oxygen in solid vanadium and niobium, containing differe nt amounts of oxygen (0.26 3.40 at.%), was studied by means of V-51 an d Nb-93 nuclear spin relaxation (NSR) measurements at 300 K < T < 1400 K. In the entire temperature range the Zeeman NSR rate 1/T1 is determ ined by fluctuations of the conduction electron nucleus interaction. T he rotating frame NSR rates 1/T1rho, however, exhibit three distinct m axima at elevated temperatures, in addition to the conduction electron induced contribution. These NSR peaks are shown to be caused by fluct uations of the nuclear quadrupole interaction of the probe nuclei due to migration of interstitial oxygen atoms. From the experimental data the corresponding activation energies E(a) and pre-exponential factors tau0 for the respective oxygen jump rates have been determined. We fo und that the atomic jump rates differ in tau0 basically, while the act ivation energies are nearly identical for all three relaxation mechani sms (almost-equal-to 1 eV). The results are discussed in the framework of three existing models for the diffusion of interstitial impurities in metals.