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Electrical properties of polymer composties: conducting polymer-polyacene quinone radical polymer
Synthetic
ELSEVIER
Metals
Electrical properties of polymer composties: Q.Leia, X.H.Yinb,
69 (1995) 357-358
conducting
K.Kobayashib,
T.Kawaib,
aHarbin Institute of Electrical Technology, department
of Electronic Engineering,
Faculty of Engineering,
polymer-polyacene M.Ozakib
quinone radical polymer
and K.Yoshinob
53 Daqing Road, Harbin 150040, China Osaka University,
2-l Yamada-Oka,
Suita, Osaka 565, Japan
Abstract Unique electrical properties are observed in conducting polymer such as poly(3-alkylthiophene) containing various types of polyacene quinone radical polymers (PAQR) such as PMA+Py. Electrical conductivity and its temperature dependence are strongly dependent on concentration of PAQR. Dependences of dielectric properties of the polymer composite on concentration of PAQR and temperature are also anomalous. The results are discussed in terms of electronic band schemes of both polymers.
1JNTRODUCTION Linearly conjugated polymers named as conducting polymer have attracted much attention because they exhibit various novel electrical and optical properties. Most these conducting polymers are semiconductors or insulators with relatively small band gap and exhibit drastic change in their properties upon doping [ 11. On the other hand, polyacene quinone radical polymer (PAQR) has also attracted much interest, because they consist of a series of condensed aromatic rings and therefore long-range delocalized electron orbital is formed. In PAQR, electrical conductivity is considered to be restricted by the inter-molecular charge transfer rate, and large dielectric constant is also evaluated. Temperature and pressure dependences of properties of PAQR has also been studied. Here, in this paper, properties of PAQR doped conducting polymer, that is, those of conducting polymer-polyacene quinone radical polymer are studied. 2. EXPERIMENTAL Various types of PAQR such as a co-polymer of pyrene with pyromellitic dianhydride and a co-polymer of anthraquinone with pyromellitic dianhydride were prepared by the method already reported[2-41. Among various PAQR, samples which consist of pyrene (Py) and pyromellitic anhydride (PMA) were mainly used in this study. Soluble and fusible conducting polymer, poly(3-alkylthiophene), was prepared utilizing FeCl, as a catalyst and purified by the method already reported[5]. Among various poly(3-alkylthiophene)s, poly(3-hexylthiophene) (PAT-6) was mainly used in this study. Purified PAQR material was ground thoroughly to tine powder and mixed well with poly(3-alkylthiophene) powder by shaking the cell containing mixture strongly. The sample was placed between electrodes, pressed and then heat treated up to melting point of poly(3-alkylthiophene). Electrical conductivity was measured by two probe method. Dielectric constant was evaluated by an impedance analyzer (YHP, 4192A).
0379-6779/95/$09.50
0
1995 Elsevier
SSDI 0379-6779(94)02484-G
Science
S.A.
All
rights reserved
3. RESULTS AND DISCUSSION Figure 1 shows dielectric constant of PAQR as a function of hydrodynamic pressure. The dielectric constant of PAQR was relatively large as expected. It should also be noted that the dielectric constant increases markedly with increasing pressure. That is, our sample exhibits typical dielectric characteristics of PAQR. Figure 2 shows temperature dependences of dielectric constant of PAT-6 containing PAQR (10%) at various frequencies. The dielectric constant of the mixture increased markedly compared with that of pure PAT-6 (about 9 at 1OOHz and 6 at 1OkHz at 20 “C). As shown in Fig.3, frequency dependence of dielectric constant of the mixture does not strongly depend on temperature. It should also be noted, by comparing with the inset of this figure, the frequency dispersion of dielectric constant of the mixture is much different from that of pure PAT-6. These facts suggest that the dielectric behavior of the mixture maintains the characteristic of PAQR itself, except for the enhancement of dielectric constant and suppression of dielectric loss, tan 6, in the mixture. As shown in the inset of Fig.4, a current voltage characteristic is linear in pure PAT-6. On the other hand, PAT-6 containing PAQR PAQR
600
.
f=lkHz
??
.
g 500
2o”c
.
2 400 s .E 300
?? ?? ??
p 200
.er
? ?
A
.
A
A
A
75%
n 100 -z
0’ 0
’
’
2
’
’
4
’
’
6
’
’
8
’
’
10
’
Pressure (kbar)
Figure 1. The dependence of dielectric constant of PAQR on pressure at various temneratures.
358
Q. Lei et nL I Synthetic
A4eta.k 69 (I995)
357-358
PAT-6 ! PAQR
100 .*-**.. 0.
150°C
20
40
60
80
100
120
140
Ill
“, 0,
‘Ok
look
1t.4
Frequency (HI,
?? .
lk
10k
1 OOk
1M
Frequency (Hz)
Temperature (“C)
Figure 2. Temperature dependence of dielectric constant of PAT-6 containing PAQR (10%) at various
Figure 3. Frequency dependence of dielectric constant of the mixture. The inset shows the case of pure PAT-6.
PAT-6 / PAQR
. -R.T
0.1
3
1
10
Voltage
100
1000
(V)
Figure 4. Current-voltage characteristic in PAT-6 containing PAQR (23%). The inset shows that in pure PAT-6.
(23%) exhibits nonlinear current(I)-voltage(V) characteristics. That is, at high voltage, I=V3R dependence was observed both at low and high temperature. In most cases, these characteristics can be explained in terms of space charge limited current (SCLC) by taking the distribution of trap states into consideration. In this case, this SCLC behavior seems to reflect characteristics of PAQR because, for such a high concentration (23%) of PAQR, percolation path seems to be formed by the PAQR channel of higher conductivity between electrodes. Figure 5 shows temperature dependence of electrical conductivity of the mixtures of various PAQR concentrations. It should be noted in this figure that electrical conductivity in the mixture is much enhanced and temperature dependence of electrical conductivity of the mixture is much different from that of pure PAT-d The anomalous behavior of electrical conductivity of PAT6 in the temperature dependence is common for PAT in the premelting region and interpreted in terms of fluctuation of electronic band scheme with temperature. In the mixture, the temperature dependence of electrical conductivity was much less for high concentration of PAQR. This result also supports that the concept of percolation can be applied to this mixture of even relatively low concentration of PAQR.
2.5
3.0 1000/l
3.5 (K-’
)
Figure 5. Temperature dependence of electrical conductivity of PAT-6-PAQR mixtures at various concentration of PAQR. 4. SUMMARY In summary unique electrical properties were found in PATPAQR mixture depending on PAQR concentration, which were explained in terms of difference in the electrical properties of PAT and PAQR themselves and also by taking the concept of percolation into consideration. Unique characteristics were also found in the electrochemical properties of PAT-PAQR mixture depending on concentration of PAQR. For example, there exist much difference in the cyclic voltammetry of PAT-6 and PAT-6-PAQR (75%) mixture. In the mixture, the effect of electron transfer to PAQR is also interpreted to plays an important role. It should also be mentioned that these electrical and electrochemical characteristics were also depending on the sort of PAQR. REFERENCES 1. K.Yoshino, K.Kaneto and Y.Inuishi, Jpn.J.Appl.Phys.,ZZ (1987) L157. 2. Q.Lei, Y.Fan and S.Shan, Sol.Stat.Commun., 79 (1991) 995. 3. H.A.Phol, A.Rembaum and A.Heney, J.Amer.Chem.Soc., 84 (1962) 2699. 4. H.A.Pohl, J.Polym. Sci., Cl7 (1967) 13. 5. R.Sugimoto, S.Takeda, H.B.Gu and K.Yoshino, Chem.Exp., 1 (1986) 635.
ELSEVIER
Metals
Electrical properties of polymer composties: Q.Leia, X.H.Yinb,
69 (1995) 357-358
conducting
K.Kobayashib,
T.Kawaib,
aHarbin Institute of Electrical Technology, department
of Electronic Engineering,
Faculty of Engineering,
polymer-polyacene M.Ozakib
quinone radical polymer
and K.Yoshinob
53 Daqing Road, Harbin 150040, China Osaka University,
2-l Yamada-Oka,
Suita, Osaka 565, Japan
Abstract Unique electrical properties are observed in conducting polymer such as poly(3-alkylthiophene) containing various types of polyacene quinone radical polymers (PAQR) such as PMA+Py. Electrical conductivity and its temperature dependence are strongly dependent on concentration of PAQR. Dependences of dielectric properties of the polymer composite on concentration of PAQR and temperature are also anomalous. The results are discussed in terms of electronic band schemes of both polymers.
1JNTRODUCTION Linearly conjugated polymers named as conducting polymer have attracted much attention because they exhibit various novel electrical and optical properties. Most these conducting polymers are semiconductors or insulators with relatively small band gap and exhibit drastic change in their properties upon doping [ 11. On the other hand, polyacene quinone radical polymer (PAQR) has also attracted much interest, because they consist of a series of condensed aromatic rings and therefore long-range delocalized electron orbital is formed. In PAQR, electrical conductivity is considered to be restricted by the inter-molecular charge transfer rate, and large dielectric constant is also evaluated. Temperature and pressure dependences of properties of PAQR has also been studied. Here, in this paper, properties of PAQR doped conducting polymer, that is, those of conducting polymer-polyacene quinone radical polymer are studied. 2. EXPERIMENTAL Various types of PAQR such as a co-polymer of pyrene with pyromellitic dianhydride and a co-polymer of anthraquinone with pyromellitic dianhydride were prepared by the method already reported[2-41. Among various PAQR, samples which consist of pyrene (Py) and pyromellitic anhydride (PMA) were mainly used in this study. Soluble and fusible conducting polymer, poly(3-alkylthiophene), was prepared utilizing FeCl, as a catalyst and purified by the method already reported[5]. Among various poly(3-alkylthiophene)s, poly(3-hexylthiophene) (PAT-6) was mainly used in this study. Purified PAQR material was ground thoroughly to tine powder and mixed well with poly(3-alkylthiophene) powder by shaking the cell containing mixture strongly. The sample was placed between electrodes, pressed and then heat treated up to melting point of poly(3-alkylthiophene). Electrical conductivity was measured by two probe method. Dielectric constant was evaluated by an impedance analyzer (YHP, 4192A).
0379-6779/95/$09.50
0
1995 Elsevier
SSDI 0379-6779(94)02484-G
Science
S.A.
All
rights reserved
3. RESULTS AND DISCUSSION Figure 1 shows dielectric constant of PAQR as a function of hydrodynamic pressure. The dielectric constant of PAQR was relatively large as expected. It should also be noted that the dielectric constant increases markedly with increasing pressure. That is, our sample exhibits typical dielectric characteristics of PAQR. Figure 2 shows temperature dependences of dielectric constant of PAT-6 containing PAQR (10%) at various frequencies. The dielectric constant of the mixture increased markedly compared with that of pure PAT-6 (about 9 at 1OOHz and 6 at 1OkHz at 20 “C). As shown in Fig.3, frequency dependence of dielectric constant of the mixture does not strongly depend on temperature. It should also be noted, by comparing with the inset of this figure, the frequency dispersion of dielectric constant of the mixture is much different from that of pure PAT-6. These facts suggest that the dielectric behavior of the mixture maintains the characteristic of PAQR itself, except for the enhancement of dielectric constant and suppression of dielectric loss, tan 6, in the mixture. As shown in the inset of Fig.4, a current voltage characteristic is linear in pure PAT-6. On the other hand, PAT-6 containing PAQR PAQR
600
.
f=lkHz
??
.
g 500
2o”c
.
2 400 s .E 300
?? ?? ??
p 200
.er
? ?
A
.
A
A
A
75%
n 100 -z
0’ 0
’
’
2
’
’
4
’
’
6
’
’
8
’
’
10
’
Pressure (kbar)
Figure 1. The dependence of dielectric constant of PAQR on pressure at various temneratures.
358
Q. Lei et nL I Synthetic
A4eta.k 69 (I995)
357-358
PAT-6 ! PAQR
100 .*-**.. 0.
150°C
20
40
60
80
100
120
140
Ill
“, 0,
‘Ok
look
1t.4
Frequency (HI,
?? .
lk
10k
1 OOk
1M
Frequency (Hz)
Temperature (“C)
Figure 2. Temperature dependence of dielectric constant of PAT-6 containing PAQR (10%) at various
Figure 3. Frequency dependence of dielectric constant of the mixture. The inset shows the case of pure PAT-6.
PAT-6 / PAQR
. -R.T
0.1
3
1
10
Voltage
100
1000
(V)
Figure 4. Current-voltage characteristic in PAT-6 containing PAQR (23%). The inset shows that in pure PAT-6.
(23%) exhibits nonlinear current(I)-voltage(V) characteristics. That is, at high voltage, I=V3R dependence was observed both at low and high temperature. In most cases, these characteristics can be explained in terms of space charge limited current (SCLC) by taking the distribution of trap states into consideration. In this case, this SCLC behavior seems to reflect characteristics of PAQR because, for such a high concentration (23%) of PAQR, percolation path seems to be formed by the PAQR channel of higher conductivity between electrodes. Figure 5 shows temperature dependence of electrical conductivity of the mixtures of various PAQR concentrations. It should be noted in this figure that electrical conductivity in the mixture is much enhanced and temperature dependence of electrical conductivity of the mixture is much different from that of pure PAT-d The anomalous behavior of electrical conductivity of PAT6 in the temperature dependence is common for PAT in the premelting region and interpreted in terms of fluctuation of electronic band scheme with temperature. In the mixture, the temperature dependence of electrical conductivity was much less for high concentration of PAQR. This result also supports that the concept of percolation can be applied to this mixture of even relatively low concentration of PAQR.
2.5
3.0 1000/l
3.5 (K-’
)
Figure 5. Temperature dependence of electrical conductivity of PAT-6-PAQR mixtures at various concentration of PAQR. 4. SUMMARY In summary unique electrical properties were found in PATPAQR mixture depending on PAQR concentration, which were explained in terms of difference in the electrical properties of PAT and PAQR themselves and also by taking the concept of percolation into consideration. Unique characteristics were also found in the electrochemical properties of PAT-PAQR mixture depending on concentration of PAQR. For example, there exist much difference in the cyclic voltammetry of PAT-6 and PAT-6-PAQR (75%) mixture. In the mixture, the effect of electron transfer to PAQR is also interpreted to plays an important role. It should also be mentioned that these electrical and electrochemical characteristics were also depending on the sort of PAQR. REFERENCES 1. K.Yoshino, K.Kaneto and Y.Inuishi, Jpn.J.Appl.Phys.,ZZ (1987) L157. 2. Q.Lei, Y.Fan and S.Shan, Sol.Stat.Commun., 79 (1991) 995. 3. H.A.Phol, A.Rembaum and A.Heney, J.Amer.Chem.Soc., 84 (1962) 2699. 4. H.A.Pohl, J.Polym. Sci., Cl7 (1967) 13. 5. R.Sugimoto, S.Takeda, H.B.Gu and K.Yoshino, Chem.Exp., 1 (1986) 635.