Crystal Structures of Silicon Nitride

Abstract

VASSILIOU and Wilde¹ have recently reported a hexagonal silicon nitride, the X-ray diffraction pattern of which differs from that of the ‘orthorhombic’ silicon nitride extracted from silicon steels by Leslie, Carroll and Fisher². After preliminary evidence of two different nitrides³, Turkdogan, Bills and Tippett⁴ have now definitely established the existence of two forms of silicon nitride, designated as α and β, with the same chemical compositions (Si₃N₄) and the same measured densities (3.19 ± 0.01 gm./ml.). Even more recently, the same two phases, I and II, as observed by Vassiliou and Wilde have been claimed by Popper and Ruddlesden⁵ to be orthorhombic and rhombohedral respectively.