Distribution of H1a-centers in as-grown diamonds of Fe-Ni-C system: FTIR-mapping study

The distribution of main nitrogen defects and H1a-centers in HPHT synthetic diamond grown by temperature gradient method (system Fe-Ni-C) has been studied by FTIR-mapping technique. The IR-peak at 1450 cm(-1) of Hla-centers (di-nitrogen interstitials), appears only in some local areas of octahedral growth sectors where single substitutional nitrogen (C-defects) was partly aggregated into nitrogen pairs (A-defects). It was found that the disappearing of H1a-centers takes place simultaneously with the completion of C -> A transformation. The observed distribution of nitrogen defects in diamonds with transition metals gives strong experimental evidence that the H1a-centers are not a by-product of nitrogen transformation, but are directly involved in the stepwise C -> A nitrogen aggregation process. Prime novelty statement: For HPHT diamond crystals of Fe-Ni-C system, the distribution of H1a centers, studied by FTIR-mapping for the first time, provide a strong argument for the interstitial-related mechanism of nitrogen C -> A aggregation. (C) 2016 Elsevier B.V. All rights reserved.