Polymeric precursors to Si3N4 were mixed with Si3N4 powder, in various combinations, to form coatings in Si3N4 and to control microstructure of Si3N4. The microstructure of polymer-derived ceramic and preceramic materials was examined by transmission electron microscopy (TEM) after heat treatment at 900°C and 1200°C and sintering at 1650°C. The observed micro-structure suggests that the polymer-derived-material properties will approach those of conventionally formed Si3N4. With proper viscosity control, gaps between α-Si3N4 powder particles as narrow as 5 to 10 nm are filled by the polymer-derived-material, ensuring full wetting of the α-Si3N4. Voids as large as 0.3 μm between (α-Si3N4 particles are filled by the ceramic precursor, reducing the size of pores formed during subsequent sintering processes. Intimate bonding between the amorphous, polymer-derived-material and the crystalline Si3N4 grains is observed after heat treatments or sintering, a necessary condition for achieving high-quality properties similar to conventional material. Acicular grains of α-Si3N4 formed from the equiaxed β-Si3N4 powder/PCMS mixture upon sintering are also observed.