D R. Riede y H Fig. 1. Crystal structure of trigonal a-Si, Na(P31c). View nearly along z-axis. Silicon atoms in red and nitrogen atoms in Fig. 2. Crystal structure of hexagonal B-Si, N,(P63). View nearly along z-axis. Silicon atoms in red and nitrogen atoms In green.14 W. Dressier, R. Riedel H ! ..J Z Fig. 1. Fig. 2. Crystal structure of trigonal ~-Si,N4 (P31c). View nearly along z-axis. Silicon atoms in red and nitrogen atoms in green. Crystal structure of hexagonal/~-Si3N4 (P6~). View nearly along z-axis. Silicon atoms in red and nitrogen atoms in green