Development of High Performance Functional Materials by Controlling Grain Boundary Character Distribution and Grain Boundary Geometrical Configuration

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The concept of "grain boundary design and control for development of high performance polycrystalline materials", which was first proposed by the present author and was recently called "Grain Boundary Engineering", has been extensively accepted as a powerful tool for achieving enhanced properties of structural materials. The aim of this project was therefore to apply the grain boundary engineering to develop high performance functional materials. The chief results obtained were as follows:(1) Effect of Magnetic Field on Grain Growth in Nanocrystalline Nickel : It has been found that a magnetic field can produce a uniform grain structure by suppressing abnormal grain growth in nanocrystalline nickel. In addition, the thermal stability of magnetically annealed sample with uniform grain structure was found to be superior to ordinarily annealed one because further grain growth rarely observed after development of a uniform grain structure by application of the magnetic field.(2)Effect of G … More rain Boundary Character/Structure on Electrical Properties of Polycrystalline Silicon : The electron beam induce current (EBIC) technique and Kelvin probe microscopy (KFM) were applied to study electrical properties of individual grain boundaries in polycrystalline silicon whose character was determined by OIM. It was found that electrical activity of grain boundaries decreased with increasing effective interplanar spacing. KFM measurements revealed that the height of potential barrier was twice higher at random boundaries than at special boundaries.(3)Effect of Grain Boundary Geometrical Configuration on Bulk Electrical Property of Polycrystalline Silicon : We introduced a new microstructural parameters "directional grain size (directional grain boundary density) and directional grain boundary character distribution" to quantitatively evaluate grain boundary microstructures with different grain boundary geometrical configuration. We found that the electrical conductivity of polycrystalline silicon decreased with increasing directional grain boundary density and directional grain boundary character distribution.(4)Control of Grain Boundary Microstructure in Iron Based Alloy by Magnetic Crystallization of Amorphous : Magnetic crystallization of amorphous iron based alloy (Fe_<78>Si_9B_<13>) was carried out to more precisely control gain boundary microstructure. It was found that a sharp {110} texture could be introduced by magnetic crystallization, which resulted in enhanced soft-magnetic properties. Less