Crystal structures and thermal properties of titanium carbo-deuterides as prepared by combustion synthesis

Titanium carbo-deuterides of various compositions have been prepared by thermal radiation and cold syntheses, and by self-propagating high-temperature synthesis. While the former methods favored the formation of a cubic structure of composition TiC0.48(1)D0.60(2) (Fm3-bar m, a=4.30963(3) A) the latter yielded a trigonal structure of composition TiC0.50(-)D0.707(4) (P3-bar m1, a=3.08208(2), c=5.04052(6) A). Differential thermal analysis and thermogravimetry data suggest the cubic structure to be thermally less stable (desorption onset temperature 823 K) than the trigonal structure (1093 K). Joint Rietveld structure refinements based on neutron and X-ray powder diffraction data show that carbon occupies octahedral interstices in the f.c.c. and h.c.p. metal atom networks of the cubic and trigonal phase, respectively, while deuterium occupies both octahedral and tetrahedral interstices in the cubic but tetrahedral interstices only in the trigonal phase. The different thermal stability of the compounds is attributed to these structural differences