N. Takahashi et M. Shiojiri, STACKING-FAULTS IN HEXAGONAL AND RHOMBOHEDRAL MOS2 CRYSTALS PRODUCED BY MECHANICAL OPERATION IN RELATION TO LUBRICATION, Wear, 167(2), 1993, pp. 163-171
The crystal structure of synthesized MoS2 was observed by high resolut
ion transmission electron microscopy to have a rhombohedral lattice of
three sandwich S-Mo-S layers of ABC stacking uniformly spaced through
0.615 nm. An extra half-plane observed in the layer lattice image fro
m an ultramicrotomed section of this crystal suggested the appearance
of a stacking fault due to a Shockley partial dislocation as in the ca
se of h.c.p. MoS2 (molybdenite). The direction of the occurrence of tr
ansformation was reversed to that in the h.c.p. MoS2 case (h.c.p.-->rh
ombohedral) by missing one layer in the rhombohedral stacking and this
transformation leads to the appearance of a stacking fault, slip, twi
nning and h.c.p. lattice formation in the slip regions, due to S-S gli
de. All these transformations have been observed in the well-determine
d orientation [2110BAR] parallel to the electron beam on an atomic sca
le. The slip mechanism was interpreted in terms of the fundamental uni
t common to f.c.c., h.c.p. and rhombohedral lattices, elucidating the
origin of easy glide in the characteristic crystal structure of MoS2.
Mo-S glide which entails deformation of the MoS2 trigonal prism was pr
oposed to form an S vacancy.