Phonons of hexagonal BN under pressure: Effects of isotopic composition

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 ${E}_{2g}$ mode frequencies has characterized. behavior analyzed by means a bond-stiffness--bond-length scaling parameter $\ensuremath{\gamma}$ which takes into consideration vast differences in $a$- and $c$-axis compressibilities. interlayer shear exhibits similar that graphite, frequency pure samples separates faster low pressures as result van der Waals interactions. Because extremely $a$-axis compressibility, intralayer rather large parameter. Within experimental uncertainties, no systematic departures related isotopic mass observed.