Isotopic phonon effects in boron-rich solids

The isotopic phonon effects in β-rhombohedral boron, boron carbide (B4.3C – B10C) and LuB12 and ZrB12 dodecaborides are analysed. Phonons based on simple movements of atoms fit the virtual crystal approximation, while complex modes deviate more or less significantly. In boron carbide these deviations are evidently mainly due to anharmonic effects, in agreement with theory. Hence the analysis of isotopic phonon shifts makes anharmonic effects measurable. Polarisation effects, stated by theory, appear to be comparably small in boron-rich structures. Phonon shifts due to isotopic disorder are determined. – The isotopic phonon effects yield valuable specific information on the nature of the different phonon modes.

Graphical abstractIsotopic phonon effects in β-rhombohedral boron.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Isotopic phonon effects in β-rhombohedral boron, boron carbide and dodecaborides. ► Separation of four different isotopic phonon effects. ► □ Boron carbide: correlations between isotopic effects and structural elements. ► Agreement between experimentally determined anharmonicity and theory.