IR-Active Phonons of Boron and Boron Carbide

Abstract

The possible IR- and Raman-active phonons of α-boron. β-boron, and boron carbide have been obtained by group theoretical methods. Reflectivity and absorption measurements in the spectral range from 10 to 1450 cm

Lattice Vibrations, MIR and FIR Optical Properties of Boron and Icosahedral Boron-Rich Borides II. β-Rhombohedral Structure Group

“…When this conception is applied to boron carbide and ß-rhombohedral boron, from In ^-rhombohedral boron it must be taken into account that the central atom B (15) In boron carbide, accordingly the 410 cm" 1 phonon (recent precise determination) can be attributed to this bending vibration of the C-B-C chain respectively of its central atom. The predominant E u character of this vibration was already stated in [36] (spectral positions there less precisely assumed at 390 cm -1 ).…”

“…As already shown in [36] the number of experimentally found distinctly discernable vibrations is considerably lower (about 24 A 2u and 25 E u ), which could be caused by different reasons:…”

“…Because of the low vibrating mass, in both cases the vibrations are distinctly shifted towards higher frequencies. It was already shown in [36] that in the dispersion analysis this absorption band cannot be described by a single vibration, but must be attributed to a double band. After in [44] the dependence of the phonon frequencies of the mass of isotopes was determined, it is possible to attribute both phonons to the 10 (4) agrees with the general isotope shift of phonon frequencies obtained in [44] (misprint in [44]: correct 1.043 instead of 1.0043).…”

“…In isotope-enriched /i-rhombohedral boron the phonon frequencies are shifted without essential change of the oscillator strength and the attenuation [44], In Fig. 5 the polarisation dependent spectra of IRactive optical phonons in pure single crystals [36] are presented as standards for the subsequent comparison with doped material. Figure 6 shows the series of spectra of Mn doped ß-rhombohedral boron.…”

“…The numbers of vibration species, which are to be expected in the main representative structures, were calculated according to the procedure described in I and [36], The first essential step is to determinate the atoms, which remain undisplaced during the different symmetry operations (Table 3). The accordingly derived numbers of vibrations in the ^-rhombohedral structure group are listed in Table 4.…”