High-resolution electron microscopy studies of the microstructure in C₄₉-TiSi₂ crystals

Abstract

The microstructure in C₄₉-TiSi₂ crystals has been studied by high-resolution electron microscopy (HREM) and electron microdiffraction. HREM images show that the crystals of C₄₉-TiSi₂ were heavily faulted on (010) planes, with a displacement of ½(a+c). In addition, 90[ddot] domains exist, which relate to the faults with a displacement of ½(a+c). There are two types of 90[ddot] domain boundary parallel to (100) or (001) plane. Type I has a sharp interface and type II has a transition zone between [100] and [001] domains, which may be explained in the light of the richness and dilution of Si atoms at the boundaries. New structures have been found which depend on the arrangement sequence of the layers with a displacement of ½(a+c) along the [010] direction of C₄₉-TiSi₂. The structure P has the Cmmm space group and the same cell dimension as C₄₉-TiSi₂, with a_p//a₄₉, b_p//b₄₉ and c_p//c₄₉. The structure S, a superstructure of TiSi₂, is formed with one unit cell of C₄₉-TiSi₂ overlapping another unit cell with a displacement of ½(a+c). The formation of the two structures is discussed.