The 29Si MAS-NMR spectra of the 3C, 6H, and 15R silicon carbide polytypes are presented and interpreted. It is shown that there are a finite number of inequivalent silicon sites which are determined by the second-and third-order carbon and first-and second-order silicon coordinations. The spectra of any other S i c polytype may now be predicted.
IntroductionHigh-resolution solid-state 29Si magic angle sample spinning nuclear magnetic resonance (MAS-NMR) spectroscopy has become a powerful and popular tool for investigating structures particularly in silicates and zeolites. This technique is equally useful for the study of non-oxide materials. To date, only 3C and 6H S i c polytypes have been studied by MAS-NMR. In this paper
The lattice dynamics and elastic moduli of diamond are reinvestigated using a method based upon an ab initio valence force field obtained for the neopentane molecule. The calculated phonon dispersion relations are in very good agreement with experiment particularly with respect to the LA, LO, TO vibrational modes. The results demonstrate the transferability of force fields from ab initio calculations on suitably chosen molecular clusters to condensed phases, and also show that a five-parameter valence force field model is sufficient to reproduce most of the features of the lattice dynamics of diamond. Excellent agreement was found between calculated and experimental bulk moduli indicating adequate modelling of the bond stretching interactions. Deviations of the transverse acoustical vibration modes at low frequencies and the remaining elastic moduli are associated with bond angle interaction terms, which may be due to the omission of a longer range interaction force constant.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.