Analytical transmission electron microscopy and surface spectroscopy of ceramics: The microstructural evolution in titanium-doped chromia polycrystals as a function of sintering conditions

摘要

Titanium-doped chromium oxide has been successfully employed in the form of thick film gas sensing devices where the porosity and surface conditioning are key aspects in providing a measurable gas response. Under normal gaseous atmospheres, where the partial oxygen pressure (p(O-2)) is approximately 0.2 atm, sintering of the host material (alpha-Cr2O3) to high densities is not possible, instead, significant grain growth occurs through evaporation-condensation transport mechanisms owing to the volatility of non-sesquioxide phases formed at high temperatures. The doping of alpha-Cr2O3 with Ti does not significantly affect the sintering behaviour of the host oxide under atmospheric conditions, but instead tends to form a nanodimensional, surface-segregated ternary phase of a nominal composition: Cr2Ti2O7, whilst the composition of grain interiors is close to pure alpha-Cr2O3. By reducing the p(O-2) to similar to 10(-15) atm during sintering, thereby reducing the formation of volatile phases, solid state diffusion mechanisms have been encouraged allowing the densification of green bodies to a density > 99% of the theoretical value. Ceramic bodies obtained by sintering in reduced p(O-2) atmospheres display a single phase solid solution, isostructural with alpha-Cr2O3 (space group R3c). (C) 2004 Kluwer Academic Publishers.