β-Si₃N₄ Microcrystals Prepared by Carbothermal Reduction-Nitridation of Quartz

Single phase β-Si₃N₄ with microcrystals was synthesized via carbothermal reduction-nitridation (CRN) of quartz and carbon coke powder as starting materials. The effects of reaction parameters, i.e., heating temperature, holding time, C/SiO₂ ratio, Fe₂O₃ additive and β-Si₃N₄ seeds on the phase transformation and morphology of products were investigated and discussed. Rather than receiving a mixture of both α- and β- phases of Si₃N₄ in the products, we synthesized powders of β-Si₃N₄ single polymorph in this work. The mechanism for the CRN synthesis of β-Si₃N₄ from quartz and the formation mechanism of Fe₃Si droplets were discussed. We also firstly reported the formation of Fe₃Si Archimedean solids from a CRN process where Fe₂O₃ was introduced as additive. Comparing to the gear-like short columnar morphology observed in samples without β-Si₃N₄ seeding, the addition of β-Si₃N₄ seeds led to an elongated morphology of final products and much finer widths. In addition, the β-Si₃N₄ microcrystals exhibited a violet‒blue spectral emission range, which could be highly valuable for their future potential optoelectronic applications.