Study of grain boundaries in polycrystalline Cr, Ta and W using nuclear gamma-resonance spectroscopy: Formation enthalpies of vacancy-oxygen complexes and single vacancies in grain boundaries, and dynamic properties of the grain boundary core in polycryst

The formation of complexes of vacancies with oxygen atoms (complexes-VacO) in the core of grain-boundary (GB) leads to a dependency of the isomer shifts δ1 of components-1 in NGR emission spectra of 57Co(57Fe) atomic probes localized in the GB core on the annealing temperature of polycrystalline metals in a technical vacuum. The formation enthalpies of complexes-VacO, Qcmpl,1, and single vacancies, QVac,1, in the GB core (states-1) in Cr, Ta and W polycrystals have been measured for the first time. Dynamic contributions to formation enthalpies QVac,1 of single vacancies localized in the GB core in the state-1 and dynamic contributions to formation enthalpies Qcmpl,i of complexes-VacO, which were localized in the lattice regions adjacent to GB’s (Adjacent Lattice Regions, ALR’s), states-2, and in the GB core, states-1, have been separated. The dynamic contribution to the formation enthalpy QVac,1 of vacancies and Qcmpl,1 of complexes-VacO in the GB core was several times smaller than the contribution to the formation enthalpy QVac,vol of vacancies in the bulk of the crystallites because of low-frequency resonance modes of local collective vibrations of intrinsic atoms in the GB core. C 2005 Springer Science + Business Media, Inc.