Structural Study of High Temperature Metal-Rich Titanium Sulfide Phases

摘要

Ti sub 2 S and Ti sub 8 S sub 3 have been prepared by high temperature annealing techniques. The crystal structures of these two phases have been determined from single crystal x-ray diffraction data. Both structures were refined using a full-matrix least-squares treatment of positional parameters and isotropic temperature factor coefficients. Ti sub 2 S crystallizes with orthorhombic symmetry, space group Pnnm, having unit cell dimensions a = 11.367A, b= 14.060A, and c = 3.326A. Ti sub 2 S is isostructural with Ta sub 2 P. Ti sub 8 S sub 3 crystallizes with monoclinic symmetry, space group C2/m, a = 32.69A, b = 3.327A, c = 19.35A, beta = 139.9 exp 0 (b - unique). Ti sub 2 S and Ti sub 8 S sub 3 have structural features similar to the features of a large number of metal-rich transition-metal chalcogenides and pnictides. These various structure types have been characterized in terms of nonmetal trigonal prismatic coordination polyhedra, eight different metal partial coordination polyhedra, a short (approximately equal to 3.4A) crystallographic axis, two unique layers of atoms containing both metal and nonmetal atom positions, and mirror planes coincident with the two layers of atom positions. The existence of a variety of structures with these structural features has led to their consideration as a unique structural class. The structural similarities and differences between the structure types of this class have been discussed in detail. Comparison of different structure types emphasized the importance of the metal bonding contribution in understanding the structural features and suggested limitations on qualitative bonding models used to understand the structural-chemical principles underlying structure stability. (ERA citation 04:019892)