What is the Crystal Structure of Titanium Silicide?

Titanium silicide(Ti₅Si₃) has a complex hexagonal structure which refers to the Mn₅Si₃ type of structure(D8₈ structure in the Schoenflies notation) with the space group P6₃ /mcm. The crystal structure is characterized by two distinct atomic chains extending along the c-axis, as shown in the figure below^[1]. 

One is a linear chain which consists of metal atoms A(1) located at (1/3, 2/3, z) where z = 0, 1/2. These A(1) atoms are coordinated by six Si atoms which, in turn, form irregular polyhedra. The other linear chain possesses A(2) atoms of trigonal antiprisms in the corners of the unit cell. The silicon atoms form interchain bonds between the A(1) and A(2) atoms to tie together the structure. Because of the complex crystal structure, titanium silicide is expected to have limitations with respect to fracture toughness and ductility at ambient temperatures in the monolithic form. Indeed, most studies on this silicide have focused on utilizing the silicide as a strengthening phase in composite forms, except the work of Frommeyer et al. and Umakoshi and Nakashima. Frommeyer et al. concluded that deformation of polycrystalline titanium silicide occurring only above 1000 °C is carried by thermally activated slip and twinning. Umakoshi and Nakashima later reported that deformation twinning of the {1¯102}<¯1101>-type is operative in single crystals with some limited loading axis orientations at high temperature above 1300 °C in compression. But, neither other slip systems nor their critical resolved shear stresses have been quantitatively identified for titanium silicide. Hence, almost nothing is known about the deformation mechanisms of titanium silicide in the monolithic form.

Reference

[1] Plastic deformation of single crystals of Ti₅Si₃ with the hexagonal D8₈ structure. Acta Materialia, Volume 58, Issue 3, February 2010, Pages 846-857.

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