Crystallite-conjugation regions and adjacent lattice regions in polycrystalline iridium: I. Composition and properties of adjacent lattice regions formed in polycrystalline iridium during annealing in an ultrahigh vacuum

In this work, we have studied the characteristics of regions in which atomic probes (APs) 57Co(57Fe) were diffusionally localized in polycrystalline iridium (poly-Ir) using a previously developed method based on Mossbauer spectroscopy. Poly-Ir becomes alloyed with oxygen during annealing even in an ultrahigh vacuum already at a temperature of 0.18T m (T m is the melting point of the matrix). After the annealing temperature reaches a certain value, there arises a “compensated” state of lattice regions adjacent to crystallite-conjugation regions (“adjacent zones,” or AZs) in poly-Ir. Such a state of AZs arises due to the mutual compensation of positive relaxation volumes of oxygen atoms and negative relaxation volumes of oxygen-vacancy complexes that are formed during each annealing. Therefore, in the “compensated” state of AZs the isomer shifts δ2 of components 2 of Mossbauer spectra of 57Fe APs become equal to “intrinsic” isomer shifts δintrs, 2 of the Mossbauer spectra of 57Fe APs located in the AZs of impurity-free metals. The “intrinsic” isomer shifts depend parabolically on the charges Z of the matrix-atom nuclei.