c-Axis conductivity and conductivity anisotropy in graphite intercalation compounds
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The stage (s) and temperature (4.23xl0 3 1.1X104 2.7 XlO 4 9.6 XlO 4 1.4X105 1.7 XlO 5 1.8 XlO 5 2.3 XlO 5 >10 6
77
J. Mater. Res., Vol. 3, No. 1, Jan/Feb 1988
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E. McRae and J. F. Mareche: Graphite intercalation compounds
TABLE II. Studies relative to 4.2-300 K investigations ofp c (fl cm) and anisotropy. Room temp.
4.2 K Pc
Notes
~3xlO 4 b
0.000 34 1
"based on ourp fl data; b s = 2-5 studied to 77 K: + TCR 2-A; - T C R for* = 5
-5X104
0.38
Inter. K
1 7
0.0008 0.17
5
0.15
KHg
1
KH
1
FeCl3
SbCl5
IC1
OsF.
-0.17 0.6
1 2 3
0.9 1.1 1.3 0.9 0.8 0.9
6 10
31
32
-2X106
33
-130
2 5 9
4
80a
Ref.
2 3 4
1.35 1.5 1.35
1
0.5-0.8
1 2
-0.05 -0.1
1
3-10
1400C
-0.02
-105
-2.5X105
-4X104
0.2 1.55" 1.9"
- 4 . 5 XlO 5
0.3 0.5 0.8 0.7 0.7 0.8
-5X105
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Value from text; experimental curves give — 2400
33 32 34
"1.4-2.6 Rvalues
35
A values to left based on our pa data and RRR = 10
-6X105
0.5 0.8 0.8 5-8X10 4
0.3-0.6
36
37
-3-4 XlO 5
38
-0.002 -0.015
39
0.3-1 X 105
mined in these earlier studies range from ~ 10—10 6 . Both pc and A decrease in stage 1 binary alkali-metal donor compounds with respect to the values for the host material, whereas in all acceptor GIC both of these parameters increase. The AsF 5 compounds have, for the past decade, been looked upon as the most anisotropic. It should be further noted that several other studies in the past have examined pc as a function of concentration, although the samples were not defined in regard to stage. Some works involved only RT measurements, others extended the study to 77 K; a number were based on graphites, the heat treatment temperatures (HTT) of which were considerably below 3000 °C. Among the intercalants are K, Br2, H 2 SO 4 , 29 and FeCl 3 . 30 More recent work has carried the lower- T limit to 4.2 K (in some cases to ~ 1.2 K) and to a wider range of materials and stages as summarized in Table II. 31 " 39 We will return to these results in the discussion below. It might also be noted that a small number of works have also dealt with pc for T> 295 K, notably in the case of the alkali-metal GIC. 40 Finally, we indicate in Table m 4 1 ^ 1 6 the compounds examined to date by our group. Some of the results have been presented elsewhere in greater detail, so we will cite here only the highlights, concentrating 78
c
particularly on the elements that appear to characterize all the materials. In regard to our work on the donor compounds, Fig. 5 gives pc (T) for the Rb-Bi family.42-43 Of the three M-Bi GIC's (M = K, Rb, or Cs), it is the rubidium group that allows synthesis of the widest range of pure stage materials.12 As for pa there is no clearpc (RT) dependence on stage; on the contrary, the
TABLE III. Summary ofpc (T) and A (T) studies carried out in Nancy. Here GBC = graphite bi-intercalation compound containing alternating layers of two different species and NR = new results presented in this article
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