Structure and crystal chemistry of Ti3SiC2

Carbide-derived layered Ti3SiCz has an unusual combination of electrical, thermal and mechanical properties. The structure of Ti3SiC2 has been refined from Rietveld analysis of neutron diffraction patterns. The c-axis stacking sequence includes double layers of distorted edge-sharing CTi6 octahedra, reminiscent of the TiC structure. The double layers are separated by square-planar Si sheets. Bond lengths and angles were measured to greater accuracy than in previous studies. The refined structure is used in conjunction with data from X-ray photoelectron spectroscopy (XPS) to hypothesize that the origin of the observed high electrical conductivity is with the Ti-C blocks. The XPS analysis shows that both Ti and C species are exceptionally well screened, even in comparison with other carbides. Also, surface-specific compositional analysis by XPS shows that freshly prepared fracture faces exhibit relatively high Ti abundance while the Si abundance is low, in comparison with expected bulk stoichiometry. (C) 1998 Elsevier Science Ltd. All rights reserved.