Organometallic precursors, an alternative route for the doping of silicon nitride powders?

Two silicon nitride powders prepared by diimide precipitation and direct nitridation were doped with 5 vol.% yttria using (i) a commercial Y2O3 powder and (ii) a soluble Y-organometallic compound as additive. The aim of this work was a direct comparison between those two doping methods. Homogeneity of additive distribution was characterized by Fourier transform infra-red spectroscopy (FT-IR), photo electron spectroscopy (XPS) and transmission electron microscopy (TEM). Depending on the doping technique used, no major difference in sintering behavior and microstructure evolution were monitored. However, chemical doping results in (i) an enhanced densification rate in the early stage of sintering, (ii) a slight shift of the densification rate maximum (ds/dt) to higher temperatures, and (iii) in a slightly finer final microstructure. Note that doping via organometallic precursors can only be successfully applied, when the powder particle surface reveals the presence of silanol groups, as in case of diimide starting powders. Electron microscopy, Organometallic dopants, Sintering, Si3N4