Dynamical behavior of intergranular glassy films (IGFs) in undoped and Lu2O3– MgO doped Si3N4 ceramics was studied by reconstructing complex-valued exit wave using focal series bright field images acquired at different temperatures during heating in-situ within transmission electron microscope (TEM). Width and value of retrieved phase change of the complex-valued exit wave across the IGFs were used to study changes that occur during in–situ heating until 950 °C. Results revealed that the IGF of an undoped sample maintains its equilibrium configuration. In the case of doped one, the phase difference between adjacent grains with IGF decreases but at the same time width of IGF increases during in-situ heating. Collectively, these two trends are indicative of the change in the mean inner potential of IGF during heating which in turn reveals that IGF in Lu2O3– MgO doped Si3N4 does not maintain equilibrium configuration. Mean inner potential differences between IGF and adjacent grain of doped samples at room temperature exhibit a higher value than that of the undoped one due to rare earth element segregation within IGF. This might be the cause of the difference in the dynamical behavior of IGFs observed in the present study. © 2019 Elsevier B.V.