Impurity states in grain boundaries and adjacent crystalline regions. III. Structure and physical properties of states localized in the cores of grain boundaries in metals.

Abstract

This paper presents the results of an investigation of the structure and physical properties of the grain boundary (GB) core in polycrystals of bcc and fcc metals by nuclear \ensuremath{\gamma}-resonance spectroscopy. The atomic probes, introduced by diffusion in the core of the GB, populate, in the polycrystals investigated here, only one state of the interstitial type. In metals, the atomic probe $^{57}\mathrm{Co}$ is a small-radius impurity, which in the GB core forms a mixed split interstitial. The average density of electrons in the GB is lower than in the lattice, which causes the Curie temperature to decrease in the GB core as compared to adjacent crystallite regions. The ``intrinsic'' properties of the GB core are modified during interstitial impurity segregation, which allows us to investigate the regularities of this important phenomenon.