Abstract:

Dynamical behaviour of intergranular glassy films (IGFs) in undoped and Lu2O3- MgO doped Si3N4 ceramics was studied by using In-situ Transmission Electron Microscope (TEM) techniques. The experiment was performed with a Zeiss-912 (LaB6, Kohler illumination) TEM, heated from room temperature to 950°C, operated at 120 KeV and equipped with an in-column energy filter (Carl Zeiss AG, Germany). Exit wave reconstruction with a set of focal series images at different temperatures was used to get more insights into IGFs. Mean full-width half maximum (FWHM) of phase changes across the IGFs and mean phase difference between adjacent Si3N4 grains and IGFs were used to study the variation during in-situ heating in case of both undoped as well as doped samples. It is shown in the results that in the case of undoped samples, IGFs maintain equilibrium configuration. In contrast, the doped one exhibits some deviation during in-situ heating, which indicates that the mean inner potential has some contribution during heating. Mean inner potential differences between IGFs and adjacent grain of doped sample at room temperature exhibit higher value than that of the undoped one due to rare earth element segregation within IGF which is possibly the cause of the difference in the dynamical behaviour of IGFs observed in the present study.