Graphite frequency distribution

Fig. 3.53 Frequency distribution of calcite-graphite fractionations (A) with increasing metamorphic grade (after Des Marais 2001)...

For the materials of greatest reactor interest (beryllium and graphite), the assumption of an isotropic frequency distribution of the normal modes is not justified. This is particularly true in graphite, where the lattice has a layer structure. The vibrations in the plane of the layers have a distribution weighted to much higher frequencies than those transverse to the lattice planes. The case of anisotropic frequency distribution with application to graphite has been considered by Schofield [18]. His model has recently... 

Fig. III.4. Frequency distribution of graphite. Drawn after data by Young and...

It is found [138] that the increase of the corrugation due to the inclusion of axially symmetric (experimentally determined bulk) quadrupole moments located at the carbon sites [361] which model the aspheiical charge distribution in the graphite substrate [see (3.9) and (3.10) in Section III.D.l] stabilizes the commensurate herringbone structure. This structure is head-tail-ordered as in Ref. 17 (see Fig. 53a or Fig. 54Z>, where the molecular axes have a systematic out-of-plane tilt) the unit cell is deformed because of the displacement of the molecular centers on the two sublattices. The Brillouin-zone-center frequency gap in the phonon spectrum is estimated [138] to amount to about 10 K in the ground state,... 

Fig. 16. Pore size distribution histograms and accumulated frequency curves of exfoliated graphite prepared by microwave irradiation at room temperature. Reprinted from Ref. [57] with permission from Carbon Society of Japan.

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