It was recalled that this material exhibited an anelastic relaxation which involved the motion of an O atom or defect. This relaxation had been studied at temperatures ranging from 200 to 550C by using internal friction techniques. Measurements of this relaxation were here extended to a new temperature regime and relaxation time range by using the mechanical after-effect method. The results covered an additional 3 orders of magnitude of relaxation time at temperatures ranging from 50 to 110C. The Arrhenius plot, when combined with internal friction results, then covered 11 orders of magnitude of relaxation time. These data could be characterized by an activation energy of 1.12eV and a pre-exponential factor of 1.9 x 10-13s. The isothermal mechanical relaxation curves which were measured here always spanned longer times than were predicted by a simple exponential relaxation. This indicated that the process was controlled by a relatively wide spectrum of relaxation times. The best approximation to this spectrum was calculated by deconvoluting the mechanical after-effect curves. The resultant distribution was symmetrical in the logarithm of the relaxation time, with a width at half-height which was a factor of 20 in relaxation time. The results were explained in terms of O mobility.

J.R.Cost, J.T.Stanley: Materials Science Forum, 1993, 119-121, 623-30