PPreparation of Color Samples of Graphite Intercalation
Compounds: Analysis and Use of Colors
Rika Matsumoto, Masato Oshima, Katsumi Yamada, Tokio Yukiya, and Masaomi
Sanekata
Tokyo Polytechnic Univ., 1583 Iiyama, Atsugi, Kanagawa 243-0297, Japan
In this study, we prepared color samples of a few typesof GICs and here we summarize their color images
together with their synthetic procedures, structures, andphysical properties. In this presentation, we mainlyintroduce the photographic images and Raman spectra werecorded of the GIC samples.

ABSTRACTGraphite intercalation compounds (GICs) exhibit
various colors depending on the materials used forintercalation and their concentrations. The color of a GIC,
which suggests its electrical properties, is the mostimportant characteristic of a GIC. In this study, we
synthesized graphite compounds with many different
types of intercalated materials, such as alkali metals,
metal chlorides, acids, and amalgams to obtain GICs that
display a range of striking colors. Here we present asummary of the color images of the GICs together with
their synthetic procedures, structures, and selected
physical properties.

2. EXPERIMENTAL
2.1 Samples
The graphite host we used mainly comprised PGS
graphite sheets (Fig.2), which are flexible and highlyoriented thin graphite sheets (Panasonic, 0.1 mm depth).
In addition, other types of graphite such as naturalgraphite powder were also used. The GIC samples weresynthesized by a vapor phase method under vacuum.
Specifically, the graphite and reagents were sealed in a
glass tube under vacuum and heated. Table 1 is the list of
prepared GIC samples with their reaction conditions.

1. INTRODUCTIONGraphite has a layered structure, with each layer
consisting of a sheet of hexagons, each of which contains
six carbon atoms. These layers form a stack of horizontal
sheets that are held together by weak bonds. Thisstructure therefore enables other chemical species toenter the space between consecutive graphite interlayers
to form graphite intercalation compounds (GICs), as
shown in Fig.1. The intercalation process is accompanied
by charge transfer between the graphite layers and theintercalated species and the number of electronic carriers,
i.e., electrons or holes, increases to 102-103 times. As aresult, the GICs have higher electrical conductivities than
the graphite host. Certain GICs have been reported tohave electrical conductivities higher than those of metalliccopper. Therefore, GICs are classified as synthetic
metals.

G01000Carbon AtomGraphite

1400

1600

1800

Raman Shift / cm-1

2000

Fig.2 Image and Raman spectrum of PGS.
Table 1 GIC samples and their reaction conditions.
TypeK-GIC
Rb-GIC
K-Hg-GIC
FeCl3-GIC
MoCl5-GIC
CuCl2-GIC
AlCl3-GIC
H2SO4-GIC*Reagents
HeatingK
200 oC, 24-72h
Rb200 oC, 24-72h
K, Hg
210 oC, 7d
FeCl3300 oC, 15-72h
MoCl5, MoO3300 oC, 24-72h
CuCl2, AlCl3
500 oC, 15h
AlCl3, C4H4ClNO2
115 oC, 24h
H2SO4, HNO3r.t., >3d* Prepared by liquid method.
2.2 Photographic images
As GICs are unstable in air, the GIC samples were kept
encapsulated in the glass tube under vacuum. The imagesof the GIC samples were captured through the glass byusing the camera of an i-Phone 7 mobile device.
2.3 Measurements
Raman spectra of the GIC samples sealed in glass cells
under vacuum were recorded to determine their stage
structure by using an NRS-5500 instrument (Jasco, 532
nm laser line). After each sample was exposed to air, itsIntercalate
Ic0.335 nm

1200

GIC

Fig.1 Graphite and GIC.
Another striking characteristic of a GIC is its color. The
appearance of graphite is black or dark gray with luster.
On the other hand, the color of a GIC depends on theintercalated species and its concentration. The color
change is also derived from charge transfer. Even though
the color of a GIC is one of its most importantcharacteristics, investigations of the color, especially color
images, have rarely been published. We believe thesedata and results to be necessary to advance thedevelopment of GICs.

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P
X-ray diffraction patterns were recorded to detect theperiod (Ic) in which the GIC could be identified. In addition,
electrical properties such as the electrical conductivity
were also measured.

AlCl3-GIC

MoCl5-GIC

FeCl3-GIC

3. RESULTS AND DISCUSSIONS
3.1 Alkali-metal GICs
Alkali-metal GICs are the most popular GICs with Li, K,Rb, and Cs easily being intercalated into the interlayers ofthe graphite structure. Figure 3 shows samples of thestage 1 and 2 structures of K-GIC prepared from PGS.
Alkali-metal GICs have a golden color in stage 1 (thecomposition is KC8) and appear blue in stage 2 (KC24).
The higher stage structures appear more dark blue toblack.
Figure 4 shows the Raman spectra of stage 1 and 2 for
Rb-GIC. The G0 band at 1580 cm-1 of the graphite
structure shifts as a result of intercalation, and the G1 andG2 bands appear at 1600 cm-1 and 1620 cm-1, respectively.
However, stage 1 alkali-metal GICs are known to exhibit
quite different Raman shifts, caused by an in-planestructure that differs from those of the higher stages [1].

Fig.5 Images of stage 1 FeCl3-, MoCl5-, and AlCl3-GICs.
G2

Stage 1
G1Stage 2
1400

1500

G2

G016001700

1800

Raman Shift / cm-1

Fig.6 Raman spectra of stage 1 and 2 MoCl5-GICs.
3.3 Other GICs
The molecules of certain acids can intercalate withgraphite. Here, we prepared H2SO4-GIC. The GIC
structure containing H2SO4 was obtained by simply
submerging a piece of graphite into a liquid mixture of
H2SO4 and HNO3 in ambient atmosphere. The resulting
GIC was blue-green in color with a slight metallic luster asshown in Fig.7 and the structure was stage 1.
Amalgams with alkali metals are also well-known
intercalates of GICs, with K amalgams reported to be pinkin color. In this work, we attempted to prepare the K-Hg
GIC with the composition KHgC4 and succeeded inconfirming the bronze-pink color, as shown in Fig.7.

Stage 1Stage 2Fig.3 Photographic images of stage 1 and 2 K-GICs.
567 cm-1
1460 cm-1

Stage 1 (RbC8)
G1

H2SO4-GIC
K-Hg-GIC
Fig.7 Images of H2SO4- and K-Hg-GIC.

Stage 2 (RbC24)

400

600

800

10001200

Raman Shift / cm-1

1400

1600

4. SUMMARY
GICs with alkali metals, metal chlorides, acids, andamalgams were synthesized by using PGS graphite
sheets and color photographic images of these GICs weretaken. In addition, their structures and properties wereinvestigated. The study is presently continuing and we aimto conduct various measurements in future. We plan toprepare additional beautiful GIC samples with HOPG
(highly oriented pyrolytic graphite) and to capture images
and carry out color measurements. We also aim toestimate the magnitude of electron transfer by measuring
the magnetoelectric properties to briefly assess therelationship between the color and these properties.

1800

Fig.4 Raman spectra of stage 1 and 2 Rb-GICs.
3.2 Metal Chloride GICs
Many kinds of metal chlorides can be intercalated toform GICs. We selected FeCl3, CuCl2, MoCl5, and AlCl3
GICs for our work, because these are easily synthesizedand form the stage 1 structure. Images of these GiCs areshown in Fig.5. The colors of metal chloride GICs, which
are darker compared with those of alkali-metal GICs, aremostly blueish green with a slight metallic luster, while
AlCl3-GIC is dark blue. The surface morphology is unevenbecause of bubbles of chlorine gas generated during thereaction. The three GICs, FeCl3-, MoCl5-, and AlCl3-GICs,
almost have the same Ic values and electrical conductivity.
Figure 6 shows the Raman spectra of the stage 1 and 2
MoCl5-GIC. Stage 1 exhibits only the G2 band, whereas
stage 2 mainly exhibits the G1 band. The stage 2 MoCl5-GIC is gray in color.

ACKNOWLEGEMENTS
The authors thank Dr. N. Akuzawa for his support insynthesizing of K-Hg-GIC samples.
REFERENCES[1] M.S. Dresselhaus, G. Dresselhaus, “Intercalation
compounds of graphite,” Adv. Phys. 30, 139-326(1981).

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