Point-Defect Relaxation in Rutile Single Crystals

Abstract

The existence of a well-defined relaxation process was established in internal friction studies of nonstoichiometric rutile, TiO2, crystals. The peak was observed only in crystals which were vacuum reduced to a room-temperature-resistivity value of 21 Ω-cm or less and oriented so that the principle vibrational strain coincided with an ``a'' crystallographic axis. All resistivity measurements were made with the current flowing parallel to the longitudinal specimen axis. For measurements in the frequency range 3 to 10 cps, the peak temperature varied from ≃60 to 85°C and exhibited a dependence on the degree of reduction, i.e., the peak temperature increased with increasing reduction. The average activation energy for the process obtained from peak shift and peak shape determinations was 24 kcal/mole. Crystallographic considerations coupled with the orientation dependence of the peak suggest that the nonstoichiometric defect in vacuum-reduced rutile is the titanium interstitial.