Structural Approach to the Problem of Oxygen Content in Alpha Silicon Nitride

The crystal structure of α‐Si 3 N 4 was reinvestigated by an X‐ray method using a single‐crystal specimen prepared by chemical vapor deposition. The oxygen content of the specimen (0.05 ± 0.03%) was determined by 14 MeV neutron activation analysis. The α form crystallizes in the space group P31c with uniteell dimensions a =7.818 ± 0.003 Å and c = 5.591 ± 0.004 Å. The structure was refined by the full‐matrix least‐squares method using 1143 observed structure factors. The Si‐N distances determind ranged from 1.715 to 1.759 Å, and the final value of R was 0.041. Structural evidences indicated that the α form is essentially pure Si 3 N 4 .