Authors: Vera G. Sursaeva
Abstract: When a bicrystal or polycrystal are subjected to a change in temperature, the individual responses of the two adjoining crystals may differ in a manner, which tends to produce a dilatational mismatch along grain boundaries. If compatibility is to be retained along the interface, an additional set of stresses must then be generated in order to conserve this compatibility. ‘Compatibility stresses’ will also be generated whenever a polycrystal is heated or cooled and the thermal expansion coefficients of the individual grains are different due to thermal expansion anisotropy. In such cases adjacent grains will attempt to change dimensions and develop mismatches by amounts controlled by the parameter Δa*ΔΤ, where Δa is the difference between the thermal expansion coefficients in the appropriate directions, and ΔΤ is the temperature change. These ‘compatibility stresses’ may be relieves if grain boundary motion, triple junction migration and grain growth are possible. These ‘compatibility stresses’ may play important role in the kinetic
behavior of the microstructure ranging from influencing the behavior of lattice dislocations near the grain boundaries to promoting grain boundary and triple junction dragging or moving. The motion of the ‘special’ grain boundaries, triple junctions with ‘special’ grain boundaries and twins under the influence of internal mechanical stresses is the main subject of this paper.
801
Authors: Cheng Ju Zhang, Jin Feng Wang, Wen Bin Su, Guo Zhong Zang, Hong Cun Chen
Abstract: The effects of Pr on the microstructure and nonlinear electrical properties of the (Co,Ta)-doped SnO2 varistors were investigated. It was found by characterizing the samples sintered at 1350 oC that the breakdown voltage increases significantly from 500v/mm to 1200v/mm, and the relative permittivity decreased rapidly from 2525 to 1199 with increasing Pr6O11 concentration from 0 to 1.20 mol%. The
analysis of samples’ microscopic structure showed that the grain size of SnO2 rapidly decreases from 5.1 to 3.7 µm with increasing Pr6O11 concentration from 0 to 1.20mol% .The significant decrease of SnO2 grain size is the main reason for raising breakdown voltage and reducing permittivity.
275
Authors: Vladimir V. Popov
Abstract: Possibilities of grain-boundary diffusion and segregation studies using nuclear gammaresonance
spectroscopy (NGR) are considered. It is shown that the results of the Mössbauer
investigations testify the necessity to specify the classical Fisher’s model of grain-boundary
diffusion, and a possible way of such specification is suggested. It is demonstrated that
investigation of grain boundaries using emission Mössbauer spectroscopy appreciably supplement
the information obtained from the diffusion profiles analysis. In particular, Mössbauer
investigations make it possible to evaluate directly the grain-boundary segregation factor, to
determine the grain-boundary diffusion mechanism, to estimate the rate of the diffusant pumping
from a grain boundary core into the bulk, etc.
497
Authors: Hidehiro Yoshida, Koji Morita, Byung Nam Kim, Keijiro Hiraga, Takahisa Yamamoto, Taketo Sakuma
997
Authors: Yoshiaki Kinemuchi, Hisashi Kaga, Satoshi Tanaka, Keizo Uematsu, Hiromi Nakano, Koji Watari
Abstract: Thermoelectric properties of zinc oxide ceramics are largely influenced by the mobility
variation because of the formation of double Schottky barrier at grain boundary. It was demonstrated
that magnetic texturing enabled to fabricate highly c-axis oriented ceramics with orientation degree of
100 MRD. This high orientation of grains resulted in periodic grain boundary structures along ab
-plane, which was confirmed by edge-on HRTEM images. Hall measurement revealed that the
mobility was enhanced at 80% by the magnetic texturing. Furthermore, it was estimated that the effect
of magnetic texturing was equivalent to the reduction in the density of trap by 5.9×1012 cm-2.
581
