Phonon spectra and thermodynamic properties of rare-earth hexaborides

The phonon spectra g(ν) of rare-earth hexaborides MeB₃ are calculated both in the approximation MeB* + B (B* = B₆) without regard for bonding between metal and boron atoms and in the approximation making allowance for this bonding. The temperature dependences of the heat capacity are calculated from the dependences g(ν), and the results obtained are compared with the experimental data in the range 5–300 K. It is found that stretching vibrations in the metal and boron sublattices and between these sublattices variously affect the thermodynamic functions of hexaborides at low and high temperatures.