ELECTRICAL-CONDUCTIVITY BELOW 3-K OF SLIGHTLY REDUCED OXYGEN-DEFICIENT RUTILE TIO(2-X)

From electrical resistivity and Hall coefficient measurements below 3 K on slightly reduced, semiconductive rutile single crystals with oxygen deficiencies O(d) between 3.7 X 10(18)/cm3 and 5.5 X 10(19)/CM3, it is concluded that the electrical conduction takes place by means of a defect-level permutation conduction mechanism involving Ti interstitial donors. In the range of 3.7 X 10(18)/CM3 less-than-or-equal-to O(d) less-than-or-equal-to 2 X 10(19)/CM3 the electrical resistivity decreases with increasing O(d), while in the range of 2 X 10(19)/CM3 less-than-or-equal-to O(d) less-than-or-equal-to 5.5 X 10(19)/cm3 it increases with increasing O(d). Values of O(d) between 8 X 10(18)/CM3 and 2 X 10(19)/CM3 correspond to the so-called intermediate concentration range of the impurity (defect) conduction, but the transition to metallic-type conduction does not occur because of a change in the defect structures, i.e., the formation of planar defects and the clustering of Ti interstitial donors at higher oxygen deficiencies.