EFFECT OF PLASTIC DEFORMATION ON THE PARAMETERS OF THE RELAXATION PEAK IN NIOBIUM IN THE TEMPERATURE RANGE 180-220K
P.P. Pal-Val, L.N. Pal-Val, V.D. Natsik, Yu.A. Semerenko
B.Verkin Institute for Low Temperature Physics
An influence of preliminary plastic deformation and low-temperature recovery on the amplitude, width and location temperature of the absorbtion peak in niobium polycrystals is investigated in the temperature range 80-300K. The measurement were carried out by the two-component oscillator technique at the frequencies of the torsional and longitudinal forced vibrations in the interval 42-370 kHz, for which peak temperature is observed within 180K<Tp<220K. The investigated samples had a resistivity ratio R300/R4.2=60 and initial dislocation dencity of order of 10-5 cm-2. Fresh dislocations were introduced by torsional deformation up to 5% at room temperature. The activation energy U=0.27 eV and the attack Frequency n0=9.2·1012 s-1 were determined from the shift of the Tp with the change of the vibration frequency. Plastic deformation results in essential increase of the amplitude, width and location temperature of the peak, while the long-term exposure at room temperature leads to a noticeable recovery of the parameters mentioned. A suggested theoretical analysis shows, that the transformation of the peak parameters may be due to a change of the dispersion of the activation energy distribution function of a corresponding relaxation process. It seems reasonable to assume, that the change is caused by dislocations introduced during plastic deformation. Dislocations provide the additional number of elementary centres of relaxation and change the dispersion of internal stresses in crystal.
Processing of the experimental data using numerical methods has allowed us to estimate parameters of the function of distribution of the activation energy local values for the samples with the different pre-history.