Amorphous and nanocrystalline titanium nitride and carbonitride materials obtained by solution phase ammonolysis of Ti(NMe2)4

Solution phase reactions between tetrakisdimethylamidotitanium (Ti(NMe2)4) and ammonia yield precipitates with composition TiC0.5N1.1H2.3. Thermogravimetric analysis (TGA) indicates that decomposition of these precursor materials proceeds in two steps to yield rocksalt-structured TiN or Ti(C,N), depending upon the gas atmosphere. Heating to above 700 °C in NH3 yields nearly stoichiometric TiN. However, heating in N2 atmosphere leads to isostructural carbonitrides, approximately TiC0.2N0.8 in composition. The particle sizes of these materials range between 4–12 nm. Heating to a temperature that corresponds to the intermediate plateau in the TGA curve (450 °C) results in a black powder that is X-ray amorphous and is electrically conducting. The bulk chemical composition of this material is found to be TiC0.22N1.01H0.07, or Ti3(C0.17N0.78H0.05)3.96, close to Ti3(C,N)4. Previous workers have suggested that the intermediate compound was an amorphous form of Ti3N4. TEM investigation of the material indicates the presence of nanocrystalline regions <5 nm in dimension embedded in an amorphous matrix. Raman and IR reflectance data indicate some structural similarity with the rocksalt-structured TiN and Ti(C,N) phases, but with disorder and substantial vacancies or other defects. XAS indicates that the local structure of the amorphous solid is based on the rocksalt structure, but with a large proportion of vacancies on both the cation (Ti) and anion (C,N) sites. The first shell Ti coordination is approximately 4.5 and the second-shell coordination ∼5.5 compared with expected values of 6 and 12, respectively, for the ideal rocksalt structure. The material is thus approximately 50% less dense than known Tix(C,N)y crystalline phases.

Amorphous and nanocrystalline titanium nitrides and carbonitrides with a very defect-rich rocksalt structure.Figure optionsDownload as PowerPoint slide