The enthalpies of formation of traditional and reconstructed small defects, having both oxygen vacancy and cation interstitial natures, were calculated for non-stoichiometric rutile. Reconstructed interstitial defects, consisting of two pairs of face-shared octahedra linked by a string of cation Frenkel defects, prove to have significantly lower formation enthalpies (per eliminated oxygen), confirming recent interpretations of electrical conductivity and high-resolution electron microscopic results.

Formation Energies of Small Defects in Non-Stoichiometric Rutile. Shen, G.J., Bursill, L.A.: Proceedings of the Royal Society A, 1986, 405[1829], 275-87