Abstract
Using synthetic near-ideal graphite obtained by hot-pressing and annealing pyrolytic material, we have prepared graphite nitrates from the first to the fourth sequence, under controlled conditions. For the first sequence compound, present determinations on form I (room temperature) agree with previous publications and confirm the stacking sequence
A
|
A
|
A
|
A
. Form I sequences 2, 3 and 4 show well defined stacking of the graphite networks, characterized by X-ray methods as follows: sequence network stacking* system unit cell (Å) space group 2
A
|
AB
|
BC
|
CA
|
A
rhombohedral
a
H
= 2⋅46
R
3
¯
m
c
H
= 33⋅45 3
A
|
ABA
|
ACA
|
A
orthorhombic
a
= 2⋅46
Cmc
2
1
b
= 4⋅26
c
= 28⋅96 4
A
|
ABAB
|
BCBC
|
CACA
|
A
rhombohedral
a
H
= 2⋅46
R
3
¯
m
c
H
= 53⋅5 * The vertical lines imply layers of intercalate. In all these compounds, the stacking sequences found can be generated from the stacking in normal graphite,
ABAB
, if the change
AB
→
A
|
A
on entry of successive intercalate layers involves the movement of a boundary dislocation through the structure. Since it is observed that the end-product (sequence
N
) under any given conditions is formed by way of a systematic numerical succession of higher sequence compounds (
N
+2,
N
+1) as intermediates, this fundamental stacking change must reverse so that
AB
⇌
A
|
A
. When any of these sequences of graphite nitrate are cooled through a
λ
transformation around —20°C, increased ordering appears in the low temperature structures (form II). Each intercalate layer now exhibits two-dimensional long range order. In addition, successive intercalated layers within any crystallite are stacked in a non-random way, which in the case of the first sequence compound implies a structure that is periodic in three dimensions. Within any intercalated layer in form I, the molecular packing resembles that in liquids. In a given crystal compound the numerical sequence of such layers is regular, and successive intercalate layers occur after
N
carbon hexagon planes. In form II, molecular packing in the intercalated layers is crystalline. Some correlation also appears between the occupied sites in different filled layers. Implications of this order-disorder transformation are briefly discussed.
Reference14 articles.
1. Proc. Roy;Soc. A,1964
2. B ottom ely M. J . P a rry G. S. U bbelohde A. R . & Y oung D. A. 1963Chem. Soc. p. 5674.
3. Proc. Roy;Cimino A.;Soc. A,1959
4. Colwell J . H . Gill E . K . & M orrison J . A. 1962 J . Chem. P hys. 36 2223.
5. H eerschap M. D elavignette P . & A m elinckx S. 1964 Carbon 1 235.
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