Nitrogen self-diffusion in silicon nitride

Self-diffusion coefficients of nitrogen in polycrystalline alpha- and beta-silicon nitride were measured by a gas–solid isotope exchange technique using 15N as a tracer at temperatures in the range 1200–1410°C. The diffusion coefficients for single-crystal grains can be expressed as D (cm2/sec) =1.2×10−12 exp(−55 700/RT) for α-Si3N4 and D (cm2/sec) =5.8×10+6 exp(−185 700/RT) for β-Si3N4. The diffusion of nitrogen along grain boundaries in the reaction-sintered materials was considerably faster than the diffusion through the bulk.