Takur\o Nakamichi1, Tokujir\o Sat\^o1 and Yukio Nagayama2
1Research Institute for Iron, Steel and Other Metals, Tohoku University, Sendai
Light Figures of (Mg, Mn)O-Al2O3 and Fe3O4 have been studied and new reagent to develop the (100) light figure was obtained for the former. To obtain light figures in (Mg, Mo)O-Al2O3, the formation of thermal etch pits is more effective, giving all of the (100), (110) and (111) light figures. The role of the chemical reagent was also carefully examined in cases of the new reagent for (Mg, Mn)O-Al2O3 and HCl for Fe3O4, and it is concluded that the specific reagent helps one or two specific side planes to develop for etch pit formation. While the character of the side plane to form an etch pit is classified into three categories, deficient, perfect and excessive, according to the crystallographic relation between the side plane itself and the related etch pit and only a perfect-type side plane is able to form a sharp etch pit and therefore a sharp light figure. The lack of the (110) light figure in (Mg, Mn)O-Al2O3 crystals etched by the new reagent and of the (100) light figure in Fe3O4 etched by HCl is interpreted under such a consideration.
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