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
& Engineering,
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.