Phonon boron compounds

Materials based on boron compounds have been explored for many decades because of their exceptional properties in respect to chemical bonding, crystal structure, and phonon and electron conduction. Especially in the field of energy conversion, electron emission, and neutron absorption, borides occupy many niches of application for which no other material can be employed. Until approximately 1980, the main interest in borides always came, however, from basic research aimed at the understanding of their electronic structure, being either responsible for the unique transport properties or the peculiarities in chemical bonding. It is, therefore, no wonder that the most information about borides was at that time created from the viewpoint of physicists and chemists. 

Table 4.1-32 Phonon wavenumbers/frequencies of boron compounds. Values for hexagonal boron nitride (BNhex) obtained from infrared reflectivity values for boron phosphide (BP) from ab initio pseudopotential calculations...

Indeed, focusing on this low thermal conductivity, Slack et al. have investigated boron cluster compounds like beta boron, YB66 among others, as possible embodiments of the "electron crystal phonon glass" systems that they have proposed (Slack et al., 1971 Cahill et al., 1989). 

Kunii, S., K. Takahashi, and K. Iwashita. 1999. Phonon and specific heat analysis in rare-earth hexaborides. ht Abstracts of the 13th International Symposium on Boron, Borides and Related Compounds, Dinard, France, p. 73. 

Taking as the only experimental parameter the CBC to CBB relation from phonon spectroscopy (53,204), the CBC, CBB and BDB concentration were calculated (Fig. 49). Subsequently the concentrations of B12 and BnC icosahedra (Fig. 50) immediately follow from the stoichiometry of the compound. The calculated BDB concentrations agree with the concentrations of B(3) vacancies determined by neutron diffraction. Compared with Fig. 26 (based on absolute oscillator strengths experimentally determined) the results in Fig. 49 and 50 (based on the quotient of oscillator strengths) show remarkable differences in the more boron-rich range only. The results in Figs. 49 and 50 are more reliable because in the quotient, systematic experimental error is largely eliminated (for details see (202)). 

R Schmechel, H Werheit, K Robberding. IR active phonon spectra of B—C.Al compounds with boron carbide structure. J Solid State Chem 133 254, 1997. 

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