Positron Annihilation Lifetime Study of Vacancies in Nb-Doped Rutile

Nb-doped rutile produced by sintering at 1400 degrees C in an air atmosphere led to a monotonic increase of the shortest tau(1) lifetime of the major spectral component from 0.17 to 0.25 ns in the Na-22 positron annihilation lifetime spectrum as the Nb doping level was progressively increased to 0.12 formula units, at which stage TiNb2O7 was observed as a second phase. The charge compensators for Nb5+ substituting for Ti4+ are indicated as cation vacancies on the basis of the increase of tau(1).