Raman scattering by crystals of rare-earth hexaborides with different isotopes of boron

Monocrystals of lanthanum hexaboride LaB$_6$ containing both natural boron and its isotopes $^{10}$B and $^{11}$B have been produced using the solution-melt method. Polyelement hexaboride rare-earths have been grown and the corresponding ceramics have been synthesized for the first time. All these crystals have been studied by means of various techniques, generally using Raman scattering. The Raman spectra attributed to various spectral lines corresponding to nonanalyzable representations have been obtained and interpreted. Frequencies and half-widths of spectral lines have been obtained, the removal of degeneracy and the development of respective splitting of degenerate oscillations induced by defects, mainly by boron isotope inclusions, have been identified. The influence of defects on the Raman spectra has been determined.