Li self-diffusion in Li 2O-deficient LiNbO 3 single crystals is investigated in the temperature range between 423 and 773 K (150-500 °C) by secondary ion mass spectrometry. A thin layer of ion-beam sputtered isotope enriched 6LiNbO 3 was used as a tracer source, which allows one to study pure isotope interdiffusion. The diffusivities can be described by the Arrhenius law with an activation enthalpy of (1.33 ± 0.03) eV, which is in acceptable agreement with the migration energy of a single Li vacancy as determined by ab initio calculations given in the literature. Charge diffusivities as derived from impedance spectroscopy measurements on the same type of samples are identical to the tracer diffusivities within error limits. No indication of the formation of defect-complexes at low temperatures could be found in the diffusion behaviour. © 2012 the Owner Societies.