The bulk diffusion coefficients were measured by means of secondary-ion mass spectrometry of Ir single crystals that had been annealed in a so-called technical oil-less vacuum at 1300 to 2000K. The Arrhenius plot could be described by:

D (m2/s) = 1.7 x 10-10exp[-193(kJ/mol)/RT]

Upon diffusion annealing in a technical vacuum, the single crystals picked up impurities which formed stable complexes with vacancies. Under these conditions, the diffusion of substitutional atomic probes was governed by impurity (rather than equilibrium) vacancies which appeared due to the thermal dissociation of vacancy-impurity complexes. The binding energy of the components of the vacancy-impurity complexes was determined to be 116kJ/mol. This value agreed with an assumed linear dependence upon the melting point of transition and noble metals that were alloyed with C and H.

A.V.Ermakov, S.M.Klotsman, S.A.Matveev, G.N.Tatarinova, A.N.Timofeev, V.K.Rudenko, N.I.Timofeev, G.F.Kuzmenko: Physics of Metals and Metallography, 2002, 93[5], 435-42