LATTICE VIBRATIONS OF BORON CARBIDES

摘要

The internal friction at low temperatures has been measured on polycrystalline samples of beta-B, B4C, B13C2, and B9C. As the carbon deficiency increases in the boron carbides, the internal friction approaches that of amorphous solids, For comparison, the internal friction of amorphous B9C, produced as a thin film by e-beam evaporation on a Si double-paddle oscillator, has also been measured, It is very similar to that of the polycrystalline B9C sample. The results are discussed in terms of glass-like lattice vibrations which have been noted before in highly disordered crystals, e.g., Ba1-yLaxF2x. It is concluded that the low thermal conductivity of B9C near room temperature which has been observed previously is indeed equal to its theoretical lower limit. (C) 1997 Academic Press. [References: 32]