Electrical Conductivity of Single and Polycrystalline Near‐Stoichiometric Rutile in the Range 600° to 1400°C

The electrical conductivity of both single‐crystal and sintered near‐stoichiometric rutile was investigated over the range 600° to 1400°C and the oxygen pressure range 0.005 to 1.0 atm. Above 1200°C, the conductivity of single‐crystal and sintered rutile obeys the relation σ∼ P o 2 −1/4 . This can be explained on the basis of the excitation of the first electron from an oxygen ion vacancy‐two trapped electron defect associated with a departure from stoichiometry. The attendant activation energy for this mechanism is 1.8 ± 0.1 ev as calculated from the In σ vs. 1 /T curves. The conductivity below about 900°C is independent of oxygen pressure and has been associated with impurity controlled defects. Activation energies of 1.0 ± 0.05 ev for the c direction and 1.5 ± 0.05 ev for the a direction and for sintered specimens were obtained for this mechanism. The electrical conductivity in the range 900° to 1200°C can be interpreted on the basis that the preceding two mechanisms act in parallel.