Crystal structure and properties of Silicon nitride
The longer stacking sequence results in the α-phase having higher hardness than the β-phase. However, the α-phase is chemically unstable compared with the β-phase. When a liquid phase is present at high temperatures, the α-phase always transforms into the β-phase. Therefore, β-Si3N4 is the major form used in Si3N4 ceramics. Abnormal grain growth may occur in doped β-Si3N4, whereby abnormally large elongated grains form in a matrix of finer equiaxed grains and can serve as a technique to enhance