Microstructure and Conductivity of Hot-Pressed Si₃N₄ - TiO₂ (TiH₂) Composites Cooled at Different Rates

Abstract

It is established that the cooling rate after hot pressing governs the crystallization and decrystallization in the Si₃N₄ - TiO₂ (TiH₂) composites. The critical cooling rate is 30 K/min for the Si₃N₄-TiO₂ composites and 50 K/min for the Si₃N₄-TiH₂ composites. It is shown that electrical conductivity responds to the evolution of composite microstructure as defect centers appear. The defects are located at the trap levels of 0.4±0.05–1.3±0.05 eV and differ in the mutually perpendicular directions. The best combination of properties is shown by the composites with a mono-trap level with the activation energy of 0.8 ± 0.05 eV. These energy levels supposedly belong to the thin layer of amorphous silicon. The nascent defects are probably point defects or association of point defects because of the low sensitivity of mechanical properties and strong response of electrical conductivity to the cooling rate.