Correlation between the Nitrogen Impurity Content and the Crystal Habit of Synthetic Diamond

Abstract

THE presence of nitrogen in diamond has provided an explanation for some of the variations which are observed in the physical properties of this material^1–3. The nitrogen impurity can exist either as dispersed substitutional donors, in which case electron spin resonance is observed², or as non-paramagnetic aggregates of atoms³. Absorption peaks in the infrared can be obtained from nitrogen in either form⁴. Peaks at 1,129 cm⁻¹ and 1,345 cm⁻¹, coupled by a broad saddle which is peaked at 1,290 cm⁻¹, are characteristic of the paramagnetic centres. In contrast, aggregates of nitrogen give a single peak at 1,280 cm⁻¹. Dyer et al.4 have shown that the two forms of nitrogen can be distinguished even if they co-exist in a particular specimen. In most cases, however, the nitrogen exists predominantly in one form and the diamond is classified either as type 1a or as type 1b. In type 1a diamond, the aggregates of nitrogen are in a majority and in type 1b diamond the concentration of dispersed nitrogen is the larger.