Crystal chemistry of layered carbide, Ti 3(Si 0.43Ge 0.57)C 2

Abstract

The crystal structure of a layered ternary carbide, Ti 3(Si 0.43Ge 0.57)C 2, was studied with single-crystal X-ray diffraction. The compound has a hexagonal symmetry with space group P6 3/mmc and unit-cell parameters a=3.0823(1) Å, c=17.7702(6) Å, and V=146.21(1) Å 3. The Si and Ge atoms in the structure occupy the same crystallographic site surrounded by six Ti atoms at an average distance of 2.7219 Å, and the C atoms are octahedrally coordinated by two types of symmetrically distinct Ti atoms, with an average C–Ti distance of 2.1429 Å. The atomic displacement parameters for C and Ti are relatively isotropic, whereas those for A (=0.43Si+0.57Ge) are appreciably anisotropic, with U 11 (= U 22) being about three times greater than U 33. Compared to Ti 3SiC 2, the substitution of Ge for Si results in an increase in both A–Ti and C–Ti bond distances. An electron density analysis based on the refined structure shows that each A atom is bonded to 6Ti atoms as well as to its 6 nearest neighbor A site atoms, whether the site is occupied by Si or Ge, suggesting that these bond paths may be significantly involved with electron transport properties.