Peculiarities in the Raman spectra of ZrB12 and LuB12 single crystals

We have measured Raman spectra of high-quality ZrnatB12, LunatB12 and Lu11B12 single crystals with high resolution, and the observed strong peaks are attributed to specific vibration modes. Besides, there are a number of additional Raman peaks in spectral ranges, where only Raman-inactive vibrations of the atomic arrangement are expected. Accordingly, it is assumed, that the investigated crystals contain intrinsic structural imperfections or distortions in sufficient concentration and efficiency to initiate the observed breaking of phonon selection rules. We suppose boron vacancies, boron isotope effects and displacements of the metal atoms to be reasons for such imperfections.