Proceedings of 2nd International Symposium for Color Science and Art 2020-2021

Preparation 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, Japansynthesis procedures, structures, and physical properties
are presented. In this presentation, we e mainly provide
the photographic images, Raman spectra, and reflectancespectra we recorded of the GIC samples.

ABSTRACT
Graphite 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 intercalating materials, such as alkali metals,metal chlorides, acids, and amalgams, to obtain GICs that
display a range of different colors. Herein, we present asummary of the colored images of the GICs together with
their synthesis procedures, structures, and selected
physical properties.

2. EXPERIMENTAL
2.1 Samples
The graphite host we used were mainly PGS graphitesheets (Fig. 2), which are flexible and highly oriented thingraphite sheets (Panasonic, 0.1 mm depth). In addition,other types of graphite such as natural graphite powder
were also used. The GIC samples were mainly
synthesized using a vapor phase method under a vacuum.
Specifically, the graphite and intercalate materials weresealed in a glass tube under a vacuum and heated.

1. INTRODUCTION
Graphite has a layered structure wherein each layer
consists 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. This
structure 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 a charge transfer between the graphite layers and theintercalated species, and the number of electronic carriers,
i.e., electrons (n-type) or holes (p-type), increases by 102
to 103 times. As a result, GICs have higher electricalconductivities than their graphite hosts. Certain GICs havebeen reported to have electrical conductivities higher thanthose of metallic copper structures. Therefore, GICs areclassified as synthetic metals.

1579

PGS
2717

500

Carbon AtomGraphite

1500

2000

2500

3000

Raman shift / cm-1

Fig.2 Image and Raman spectrum of PGS.
2.2 Photographic images
As GICs are unstable in air, the samples were kept
encapsulated in the glass tube under vacuum. The imagesof the GIC samples were captured through the glass.
2.3 Measurements
Raman spectra of the GIC samples sealed in glass cells
under a vacuum were recorded to determine theirstructure using an NRS-5500 instrument (Jasco, 532-nm
laser line). Reflectance spectra were also measured usinga thin-film measurement system F20 (FILMETRICS). Aftereach sample was exposed to air, its X-ray diffraction
patterns were recorded to detect the period (Ic) in which
the GIC could be identified.

Intercalate
Ic0.335 nm

1000

GIC

Fig.1 Graphite and GIC.

3. RESULTS AND DISCUSSIONS
Table 1 presents a list of prepared GIC samples with
their compositions [1] and colors.
3.1 Alkali-metal GICs
Alkali-metal GICs are the most widely-used GICs.
Figure 3 shows samples of the stage 1 and 2 structures ofK-GICs prepared from various graphite materials.
Alkali-metal GICs have a golden color in stage 1 and ablue color in stage 2. The alkali-metal atoms intercalate all

Another striking characteristic of a GIC is its color. The
appearance of graphite is black or dark gray with luster. In
contrast, the color of a GIC depends on the intercalated
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 important characteristics, their color
images have rarely been published. We believe these data
to be necessary to advance the development of GICs.
In this study, we prepared color samples of several
types of GICs and their color images together with their25

Proceedings of 2nd International Symposium for Color Science and Art 2020-2021
generated during the reaction. The three GICs, namely
FeCl3-, MoCl5-, and AlCl3-GICs, have almost identical Ic
values and electrical conductivities.

interlayers in the stage 1 structure and are present inevery other interlayer in stage 2.
Figure 4 shows the reflectance spectra of stages 1 and2 for AM-GICs with AM = K, Rb, and Cs. The golden color
in stage 1 reflects wavelengths longer than 480 nm, while
the blue stage 2 compounds reflect light with wavelengths
longer than 750 nm.

1632

H2SO4-PGS
1632

AlCl3-PGS

Table 1 GIC samples prepared in the present study.
TypeIntercalate
LiComposition
LiC6
LiC18
AM = K, Rb, Cs AMC8AMC24Ca
CaC6K-Hg
KHgC4
FeCl3
C6.1FeCl3
MoCl5
CxMoCl5
CuCl2C4.9CuCl2
AlCl3
C8.3AlCl3
AlCl3-CuCl2--H2SO4--Br2---np1624

MoCl5-PGS

ColorGoldBlue
GoldBlue
SilverGold ~ Pink
Blue-green
Blue-green?
Blue
Blue-green
Blue-green
Black

1623

FeCl3-PGS
1500

AlCl3-GIC

3.3 Other GICs
The molecules of certain acids can intercalate withgraphite. Here, we prepared H2SO4-GIC using a liquid
method. The GIC structure containing H2SO4 wasobtained by simply submerging a piece of graphite into aliquid mixture of H2SO4 and HNO3 in an ambient
atmosphere. The resulting GIC was blue-green in color
with a slight metallic luster as shown in Fig. 6, and thestructure was stage 1 considering the Raman spectrum
shown in Fig. 5.
Amalgams with alkali metals are also well-known
intercalates of GICs, and K amalgams have been reported
to be pink in color. In this work, we attempted to prepare
the stage 1 structure of K-Hg-GIC with the composition
KHgC4 and succeeded in confirming its bronze-pink color.

Reflectance

Reflectance

KC24

RbC8

RbC24

CsC8
CsC24500

600700

Wavelength / nm

800900500

600700800

H2SO4-GICFeCl3-GI
C Photographic images of p-type GICs.
Fig.6

Stage 2KC81800

Fig.5 Raman spectra of p-type GICs.

Fig.3 Photographic images of stage 1 and 2 K-GICs.
Stage 11700

Raman shift / cm-1

Stage
2Stage11600

4. SUMMARY
GICs with alkali metals, metal chlorides, acids, andamalgams were synthesized using PGS graphite sheets
and colored photographic images of these GICs wereobtained. In addition, their structures and properties wereinvestigated. This study is still ongoing, and we plan toprepare additional GIC samples with highly orientedpyrolytic graphite (HOPG) and to obtain images of thesesamples. We also aim to estimate the magnitude ofelectron transfer to briefly assess the relationship between
the color and these properties.

900

Wavelength / nm

Fig.4 Reflectance spectra of stage 1 and 2 AM-GICs.
3.2 Metal Chloride GICs
Many kinds of metal chlorides can be intercalated toform GICs. We selected FeCl3, CuCl2, MoCl5, andAlCl3-GICs in this study because they are easily
synthesized and form stage 1 structures. Figure 5 showstheir Raman spectra. The GICs with a stage 1 structure
exhibit only the G2 band around 1620 cm-1.
Images of these GICs are shown in Fig. 6. The colors ofthe metal chloride GICs, which are darker compared withthose of alkali-metal GICs, are mostly blueish green with aslight metallic luster, while AlCl3-GIC is dark blue.
Therefore, their reflectance spectra measurements weredifficult to obtain. In addition, the surface morphology isuneven due to bubbles of chlorine gas that wereACKNOWLEGEMENTS
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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