Cuscó R, Pellicer-Porres J, Edgar JH, Li J, Segura A, Artús L. Phonons of hexagonal BN under pressure: Effects of isotopic composition. Phys Rev B. 2021;103(8):85204. doi:10.1103/PhysRevB.103.085204
Raman scattering experiments on isotopically enriched hexagonal boron nitride have been performed under pressure up to 11 GPa at room temperature. The sublinear increase of the Raman-active E2g mode frequencies has been characterized. The pressure behavior has been analyzed by means of a bond-stiffness–bond-length scaling parameter ? which takes into consideration the vast differences in a- and c-axis compressibilities. The interlayer shear mode exhibits a ? parameter similar to that of graphite, and the mode frequency in isotopically pure samples separates faster at low pressures as a result of van der Waals interactions. Because of the extremely low a-axis compressibility, the intralayer mode exhibits a rather large scaling parameter. Within experimental uncertainties, no systematic departures related to isotopic mass have been observed.
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