V.N. Kaigorodov

NGR Investigation of Grain-Boundary Diffusion in Poly- and Nanocrystalline Nb

The properties of grain boundary cores and adjacent areas in polycrystalline Nb manufactured by rolling with subsequent recrystallization annealing and nanocrystalline Nb obtained by high pressure torsion have been investigated by the Mössbauer emission spectroscopy on 119mSn nuclei.

Segregation of 57Co Atomic Probes in the Cores of Grain Boundaries in d-Transition Metals

A new method, which has been developed to examine the structure and physical properties of cores of grain boundaries (GBs) (S.M. Klotsman, Sov. Phys. Uspech. 33, 55 (1990); V.N. Kaigorodov and S.M. Klotsman, Phys. Rev. B 49 (1994)), was used to study segregats localized in two discrete regions of polycrystals: cores of GBs and two-dimensional regions of the lattice adjacent to the GBs. This paper reports and discusses results of investigations of segregation of 57Co atomic probes in cores of GBs in the d-transition metals Cr, Ta and W. The interaction of 57Co APs with GBs cores in metals is similar to their interaction with vacancies, because GBs cores are characterized, as vacancies in metals, by an excess volume and a negative charge. GBs are enriched with 57Co in chromium and tungsten. The activation enthalpy of the 57Co atomic probes segregation at GBs in Cr and W is proportional tothe local magnetic moment of 57Co atomic probes. GBs cores are found to be depleted of 57Co atomic probes in Ta.

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 Mössbauer spectroscopy. Poly-Ir becomes alloyed with oxygen during annealing even in an ultrahigh vacuum already at a temperature of 0.18Tm (Tm 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 Mössbauer spectra of 57Fe APs become equal to “intrinsic” isomer shifts δintrs, 2 of the Mössbauer 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.

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

Composition and properties of cores of crystallite-conjugation regions (CCRs) formed during annealing of polycrystalline iridium (poly-Ir) in an ultrahigh vacuum (UHV) have been studied using the method of intercrystalline diffusion in combination with Mössbauer spectroscopy (ID+MS) that has been developed in our previous works. Upon annealing in a UHV, poly-Ir is doped with oxygen from the atmosphere of the vacuum chamber. Complexes containing two vacancies per oxygen atom are formed in the CCR cores of poly-Ir because of a rearrangement of the atomic structure of the CCR cores upon their doping with oxygen. Using the ID+MS method, we for the first time revealed a “compensated” state of CCR cores in poly-Ir samples annealed in a UHV and of CCR cores in poly-Cr annealed in technical vacuum. The cause of the appearance of “compensated” states in CCR cores is the mutual compensation of relaxation volumes with opposite signs characteristic of different point defects. The relaxation volume of an oxygen atom in the CCR core of poly-Ir is by an order of magnitude greater than that in poly-Cr.

Mössbauer spectroscopy of interphase boundaries of Co/CoO bilayers

Co films and Co/CoO bilayers that were deposited by the method of magnetron sputtering on the MgO(100) and Al2O3(110) single-crystal substrates have been studied using electron microscopy and Mössbauer spectroscopy. The surface, bulk, and interphase Mössbauer spectra of the layers and bilayers under examination have been investigated. It is shown that the 57Co(57Fe) atoms located in the region of a Co/CoO interphase boundary can be in different magnetic states and have different valences and chemical surroundings.

Super-High Concentrations of Vacancies in Regions of High Concentration of Point Defects and Composition of Vacancy-Oxygen Complexes in These Regions in Pd, Ta, W and Pt Polycrystals

The delivery of vacancies from the core of crystallite conjugation regions (CCRs) to the region in the crystallite volume with a high concentration of point defects (HCPD), which is adjacent to the CCRs core, limits the formation of oxygen-vacancy complexes in the HCPD region in Pd, Ta, W and Pt. The number of partners in complexes having a minimum size, which depended on the formation temperature of the complexes, was estimated. At a temperature sufficient for full compensation of relaxation volumes of point defects in the HCPDR lattice, the complexes consisted of one oxygen impurity and three vacancies. At the detection threshold temperature, the complexes included only one vacancy and two oxygen impurities. The formation activation enthalpy of the vacancies in the HCPD region accounted for about 15% of the formation activation enthalpy of equilibrium vacancies in the bulk and exhibited a linear dependence on universal homologous tempera-