Metastable SiCN glass matrices studied by energy-filtered electron diffraction pattern analysis

Bulk SiCN glasses, derived from polymer precursors with tailored architectures, were characterized upon pyrolysis at 1000 °C and subsequent annealing at 1400 °C and 1540 °C. The characterization tools employed were high-resolution transmission electron microscopy (HRTEM) imaging and energy-filtered selected area electron diffraction (EF-SAED). Main emphasis of this work was to verify as to whether the intrinsic amorphous structure of polymer-derived bulk materials exhibits different structural features upon pyrolysis, that depend on the functionalities of the pre-ceramic polymer, and whether such characteristic features are maintained upon high-temperature anneal. HRTEM imaging did not reveal any pronounced variation between the different SiCN glass structures after the organic–inorganic transition at 1000 °C or even upon heat treatment at 1400 °C. However, EF-SAED analysis showed differences in the amorphous structure of the four polymer-derived SiCN glasses studied even upon thermolysis at 1000 °C. The evolution of the electron diffraction intensity profiles of the EF-SAED patterns after subsequent thermal treatment at elevated temperatures showed clear evidence of structural rearrangements within the SiCN glass networks upon annealing at temperatures exceeding the pyrolysis temperature. The experimental results provide evidence that the metastable glass structure of polymer-derived SiCN ceramics depends on the starting polymer employed and, in addition, that the intrinsic glass architecture affects the thermal stability (onset of crystallization) of the amorphous matrix.