High pressure and high temperature modulation of electrical conductivity in high hardness silicon nitride-carbon composites

Electrically conductive silicon nitride ceramics with both high hardness and electrically conductive properties are promising advancing ceramics. However, ensuring the high hardness while simultaneously enhancing their electrical conductivity poses a great challenge. In this work, Si 3 N 4 -carbon composites with different carbon content were synthesized with diamond phase transformation method under high pressure and high temperature (HPHT). The α→β phase transition in silicon nitride enables the coexistence of α/β phases, offering a hardness of up to 23.15 ± 0.08 GPa, comparable to dense silicon nitride ceramics and significantly higher than synthesized silicon nitride-graphite composites. Diamond uniformly distributed in the silicon nitride matrix is graphitized at high temperatures to form conductive channels, reducing resistivity to 2 × 10 - ⁴ Ω∙m, over a dozen orders of magnitude lower than pristine silicon nitride. This phase transition sinter mechanism provides a method for designing conductive Si₃N₄-based ceramics with high hardness.