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Hexagonal boron nitride (hBN) crystals enriched in 10B and 11B isotopes were synthesized using a high temperature (1500° C) Ni-Cr-B reactive-precipitation growth under a N2 atmosphere. Two growth mechanisms were observed: conventional defect-facilitated bulk growth which produced crystals with a platelet-like habit with width and thickness of 20-30 μm and 5 μm, respectively, and vapor-liquid-solid interface growth of hBN whiskers with lengths and diameters as large as 70 μm and 5 μm, respectively. Similar growth mechanisms were seen for samples enriched in either isotope. Isotopic analysis via secondary-ion mass spectrometry showed boron concentrations of 84.4 at% and 93.0 at% for the majority isotopes in the 10B-rich and 11B-rich samples, respectively. Raman spectroscopy showed an increase in peak Raman shift for the 10B-rich sample, having two barely resolved peaks at 1393.5 and 1388.8 cm-1, and a decrease for the 11B-rich sample, having peak at 1359.5 cm-1 (FWHM of 9.4 cm-1), compared to that of natural hBN, with its peak at 1365.8 cm-1 (FWHM of 10.3 cm-1). Raman shift showed a linear trend with increasing 10B concentration allowing for a calibration curve to be developed to estimate 10B enrichment in hBN using non-destructive methods.

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