Low-Temperature Dissipation Peak in Niobium

Abstract

The energy dissipation coefficient ${Q}^{\ensuremath{-}1}$ and the resonant frequency of a circular plate of niobium have been measured as a function of temperature in the range 60-300\ifmmode^\circ\else\textdegree\fi{}K. The measurements have been carried out at four different frequencies from 18 kc ${\mathrm{sec}}^{\ensuremath{-}1}$ to 174 kc ${\mathrm{sec}}^{\ensuremath{-}1}$ with strain amplitudes smaller than ${10}^{\ensuremath{-}7}$. For each vibration mode a pronounced peak is found for the dissipation coefficient while the frequency-temperature curves show a corresponding inflection. The temperature ${T}_{m}$ of the dissipation peak depends on the vibration frequency according to an Arrhenius equation which characterizes the thermally activated relaxation effects.The activation energy $\overline{W}$ and the limiting relaxation time ${\overline{\ensuremath{\tau}}}_{0}$ of the process have been computed and these values [$\overline{W}=0.265$ ev and ${({\overline{\ensuremath{\tau}}}_{0})}^{\ensuremath{-}1}=61\ifmmode\times\else\texttimes\fi{}{10}^{11}$ ${\mathrm{sec}}^{\ensuremath{-}1}$] are in agreement with the values previously found in some fcc metals for the relaxation effect due to the motion of dislocations.The value of $\overline{W}$ found in niobium shows that the effect cannot be directly produced by the motion of interstitial atoms of hydrogen.