Self-diffusion coefficient nitrogen

Silicon nitride is a highly covalent bonded compound with self-diffusion coefficient of the nitrogen atoms of 6.3 x 10 2(1 cm2/s at 1400°C.22 Therefore, densification without any sintering additives is nearly impossible. In 1961, Deeley and Herbert.23 was the first to report that Si3N4 ceramics could be... 

In the past, attempts to prepare such ternary nitrides by reaction of the respective binary nitrides always have failed because the binary nitrides do not melt congruently and also because of the low self-diffusion coefficients of these materials. However, for the synthesis of SiPNj a molecular precursor Cl3SiNPCl3 has been proven to be specifically useful [5]. In this compound the required structural element of two vertex sharing tetrahedra centered by phosphorus and silicon and connected via a common nitrogen atom is pre-organized on a molecular level. The precursor compound is obtained (Scheme 3) in a three-step synthesis starting from ((CH3)3Si)2NH which is commercially available. 

E. B Winn, The Temperature Dependence of the Self-Diffusion Coefficients of Argon, Neon, Nitrogen, Oxygen, Carbon Dioxide, and Methane, Phys. Rev., 80 1024,1950. 

TaWe 1. Self-diffusion coefficients of carbon, nitrogen, and silicon in Si3N4 and SiC [6-8]... 

Gal N/Gal N/Gal N isotope heterostructures were used to study nitrogen self-diffusion by secondary-ion mass spectrometry and thermally activated decomposition. After interdiffusion of Ga N and Ga N layers at between 770 and 970C the diffusion profiles were measured. The temperature dependence of the nitrogen self-diffusion coefficient in hexagonal GaN was described by ... 

Self-diffusion coefficients of nitrogen in polycrystalline alpha- and beta-silicon nitride were measured by using a gas-solid isotope exchange technique with as a tracer at 1200 to 14IOC. The diffusion coefficients for single-crystal grains could be expressed as ... 

It is clear Ifom Fig. 7 that the silicon self-diffusion coefficient in undoped crystals is lower than in doped crystals. An opposite dependence was observed for the carbon self-diffusion coefficient. According to the law of acting masses, the silicon vacancy (acceptor) concentration increases with increasing donor dopant concentration (nitrogen). AU this leads to an increase in the diffusion coefficient in the presence of a vacancy mechanism of self-diffusion. Carbon vacancies are donors, and their concentration decreases when the donor concentration is increased. This leads to a decrease in the carbon self-diffusion coefficient. 

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