0)b-SiC),
dashed lines show the carbon interlayer.ARRANGEMENT OF SUPERSTOICHIOMETRIC CARBON IN STRUCTURE OF SIC
O. Mykhaylyk, M. P. Gadzira
Institute for
Problems of Materials Science, Ukrainian National Academy of
Sciences, Krzhyzhanivskogo 3, 252680 Kyiv, Ukraine
Silicon carbide (SiC), existing in a number of
different polytypic forms, have small deviations from
stoichiometric composition SiC-C, which practically do not
influence on lattice parameter [1]. However, the existence of SiC
with superstoichiometric carbon occupying the silicon sublattice
sites (Csi or carbon antisites) was demonstrated in
[2] where by alteration of deposited gas mixture in CVD process
was created pirolitic SiC with carbon rich layers characterised
by decreased lattice parameter (a ³ 4.347 Å) in comparison
with standard cubic b-SiC one (a = 4.359 Å). This opportunity of SiC-C solid
solution formation is confirmed by the theoretical work [3] where
it is shown that among native defects of SiC structure the minima
energy formation has Csi.
Fig. The model of SiC-C structure (projection
onto (10)b-SiC),
dashed lines show the carbon interlayer.
Recently [4,5], we had synthesised the SiC-C
fine powder, where carbon in reaction mixture was in unusual
state (wrinkled graphite layers produced by the thermal expanding
of sulphuric graphite). This synthesised powder material allow to
carry out different structure investigation, in particularly,
X-ray microstructure analysis and lattice parameter measurements.
The synthesised SiC-C is characterised by the lattice parameter a
= 4.3540(2) Å and mean-squared strain <e2>1/2
= 1.3´10-3 (the strain field model suggested in [6]
was used). The presence of the first and the second class defects
(Krivoglaz classification) in structure simultaneously could be
described by the correlated between one another first class
defects (in particularly, Csi). The suggested model (Fig.) is
based on the location of superstoichiometric carbon along silicon
carbide's close-packed planes of {111}. Considerably less
interatomic C-C distance in comparison with Si-C one leads to the
decrease of the lattice parameter and, in addition, the infinite
carbon interlayers create the strain fields. Thus, the solid
solutions row of silicon carbide with diamond-like structure
compounds (SiC-AlN, SiC-BeO) could be added by SiC-C (silicon
carbide-diamond).
On the bases of microstructure analysis and
precision lattice parameter measurements it is revealed that
SiC-C is destroyed at heating in vacuum in temperature range of
graphitization of diamond. After sintering at high pressure (4-8
GPa) and high temperature (1673-2073 K) SiC-C is maintained. In
addition, the microstructure investigations of the sintered
samples shown, that the superstoichiometric carbon atoms in SiC
structure arrange not only as planar defects but as
non-correlated point defects. The last followed by decreasing
lattice parameter simultaneously (down to 4.35234(5) Å).