Effect of synthesis conditions of BCNO on the formation and structural ordering of boron nitride at high temperatures

Highlights: • Correlation between BCNO synthesis conditions&BN formation at high temperatures. • Increase in H₃BO₃:C₃H₆N₆ ratio promotes BN formation and its structural ordering. • Increase in post heating temperature promotes BN formation. • BN synthesis with varied 3-D structural ordering, particle size and morphologies. -- Abstract: We have investigated the effect of synthesis conditions of BCNO compounds on BN formation and its structural ordering. BCNO compounds were synthesized from boric acid (H₃BO₃)-melamine (C₃H₆N₆) mixtures with various molar ratios (H₃BO₃:C₃H₆N₆ = 1:1 to 6:1) at 400 °C. The BCNO compounds were then subjected to post heating between 1400 °C and 1800 °C under argon flow. The final products were crystalline BN with hexagonal symmetry exhibiting varying degrees of structural ordering. As the H₃BO₃ to C₃H₆N₆ ratio in the starting composition is increased, BN formation temperature decreases and the structural ordering of BN increases. Post heating at higher temperature also promotes BN formation and structural ordering. The findings indicate that synthesis and structural ordering of BN can be tailored by controlling starting composition and post heating temperature. These observations may provide a guideline to synthesize high or low-density polymorphs of BN at reduced pressure, temperature, or both.