Dielectric Dispersion in Ferroelectric Composite Nanocrystalline Cellulose – Triglycine Sulfate Nguyen H.T., Sidorkin A.S., Milovidova S.D., Rogazinskaya O.V. Voronezh State University Voronezh, Russia
[email protected]
NCC+TGS at room temperature there is a strong dispersion of dielectric permittivity presumably due to the Maxwell-Wagner polarization mechanism [7]. In favour of the specified mechanism, in particular, said the maximum of dielectric loss in the composite NCC+TGS at frequencies close to the reverse charging time of capacitors, that is related to different layers of the composite, through the active circuit resistance. In order to add to the previous study of dielectric dispersion in the composite NCC+TGS in infra-low frequency range in present work we have carried out comparative investigations of dielectric dispersion in pure TGS, NCC, and in ferroelectric composite NCC+TGS in the range of higher frequencies 103 – 106 Hz in a weak electric field (1 V.cm-1) in the range from room temperature to the phase transition temperature of this composite.
Abstract—The dispersion of dielectric permittivity of the composite nanocrystalline cellulose – triglycine sulfate in the frequency range 103 – 106 Hz in a weak electric field in the range from room temperature to the phase transition temperature of this composite (+54 º) was investigated. It was shown that the typical for triglycine sulfate maximum of the imaginary part of dielectric permittivity at frequencies (105 Hz - 106 Hz) in the case of composite nanocrystalline cellulose – triglycine sulfate lies at lower frequencies (104 Hz - 105 Hz). Index Terms— nanocrystalline cellulose, dielectric relaxation, composite, dielectric permittivity.
I. INTRODUCTION The composite materials with ferroelectric inclusions now are the object of study in numerous investigations, that is substantially related to a wide range of their possible applications due to large potential variations in properties of these composites by changing the material characteristics and geometry of the coupling of their components. The most commonly matrices in ferroelectric composites are still porous aluminum oxide, silicon and glass [1 - 3]. Recently, to these traditional matrices added chemically pure nanocrystalline cellulose (NCC) with unique properties, that are approved in various medical and engineering fields [4,5]. The nanocrystalline cellulose belongs to the monoclinic system (d = 0,61 nm), the crystallographic plane (–110) of its unit cell is parallel to the sample surface. The microfibrillar ribbons NCC play a role not only of the reinforcing grid, but also of the hydrophilic layers, which are able to absorb on their surface a large number of water molecules as well as other water-soluble compounds. The sorption and desorption properties of cellulose are explained by the orientation of its microfibrillar ribbons and a large number of nanochannels between them. These ribbons consist of a large number of nanofibrils with a width of 50-100 nm and a length exceeding the width of a thousand or more times, that is formed from the faces (–110) and (110) with high surface energy caused by the primary – groups on these faces [4]. The authors of this paper previously showed the possibility of creating composites based on nanocrystalline cellulose with triglycine sulfate (NCC+TGS) [6,7]. In these studies the expansion of ferroelectric phase in these composites from 5º to 7º as compared with monocrystals TGS ( = +49 º) was found. In low and infra-low frequency range (10-3 – 103 Hz) in
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II. SAMPLE PREPARATION AND METHODS The studied samples were prepared as previously described [6] as follows. From initial NCC gel films water was removed by filter paper to reduce the thickness of the samples approximately by twice. The saturated TGS solution heated to +50º was introduced into these NCC pieces with nanochannels oriented perpendicular to the large surface of the samples, drop by drop in several stages, each time to complete absorption from both sides. The prepared samples were heated to +100º, kept for 3 hours at this temperature and then dried at room temperature. The filling of nanochannels NCC by TGS was controlled by x-ray investigations. The dried composite films with a thickness ~ 0,3 ÷ 0,4 mm were cut into samples with a surface area of ~ 35 mm2. Silver leaf electrodes were applied on the prepared samples by using a conductive glue. The frequency dependence of the real '(f) and the imaginary "(f) parts of the complex dielectric permittivity *(f) = '(f) + j"(f) was measured by using Impedance/GainPhase Analyzer “SOLARTRON SI 1260” with Solartron Dielectric Interface 1296 at frequencies f = 103 – 106 Hz in a weak electric field with an amplitude of 1 V.cm-1. The measurement error did not exceed 1%. The dielectric measurements were carried out in the range from room temperature to the phase transition temperature of this composite (+54 º).
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In the studied frequency range 103 - 106 Hz the obtained amplitudes of the dispersion of dielectric permittivity in the composite NCC+TGS are small enough as compared with single crystal TGS. Unlike pure TGS, the values of both ' (curve 2, Fig. 1a) and " (curve 2, Fig. 1b) in the composite NCC+TGS at room temperature monotonically decrease with increasing frequency. The typical for single crystal TGS maximum "(f) in the case of composite NCC+TGS at room temperature is absent (curve 2, Fig. 1b). At the same time the Cole-Cole diagram for composite NCC+TGS, similar to the single crystal TGS and has two sections of this dependence (Fig. 2). The first one lies on the arc in the frequency range from 6.3 Hz to 1 Hz (curve 3, Fig. 2) and the second one (1Hz – 3.9 Hz), unlike the single crystal TGS, is a linear dependence of " on ' (curve 4, Fig. 2). According to the experimental data the specified linear dependence "(') in the composite NCC+TGS is observed up to 10 Hz (in Fig. 2 is not shown). The values of " ' in the matrix NCC are small enough as compared with the composite NCC+TGS and single crystal TGS, and practically unchanged when the frequency change (curves 3 in Fig.1a and Fig. 1b). At higher temperatures in the frequency dependencies of the imaginary part of dielectric permittivity "(f) in the composite NCC+TGS the appearance of the typical for single crystal TGS maximum (Fig. 3b) is observed, which becomes more pronounced with increasing temperature. In addition, as shown in the Cole-Cole diagram (Fig. 4), the Debye-like relaxation here dominates and also becomes more pronounced with increasing temperature. Conversely the section of linear dispersion is less pronounced and completely disappears at the phase transition temperature of the composite NCC+TGS (+54 °C) (Fig. 4c). As we have seen that the presence of maximum "(f) and Debye-like relaxation of the composite NCC+TGS in the studied frequency range are typical for single crystal TGS relaxation behavior too. At the same time, the observed maximum "(f) in the composite NCC+TGS lies in the range of lower frequencies (from 104 Hz to 105 Hz) (Fig. 3b) as compared with the single crystal TGS (from 105 Hz to 106 Hz) [8].
III. EXPERIMENTAL RESULTS AND DISCUSSION All the obtained ferroelectric composites nanocrystalline cellulose – triglycine sulfate are characterized by the smearing of the phase transition and its shift to higher temperatures as compared with single crystal TGS. In the entire range of studied temperatures the values of dielectric permittivity of composites NCC+TGS are less than of single crystal TGS [6,7]. The obtained results of frequency dependencies of the real '(f) and the imaginary "(f) parts of the complex dielectric permittivity in single crystal TGS, composite NCC+TGS and matrix NCC at room temperature are shown at Fig. 1. The dielectric dispersion of single crystal TGS in the studied frequency range has Debye-like character [8]. The values of ' monotonically decrease with increasing frequency (curve 1, Fig. 1a) in the presence of a maximum "(f) (curve 1, Fig. 1b). The Cole-Cole diagram for single crystal TGS plotting in the studied frequency range at room temperature are characterized by two arcs (curves 1, 2 in Fig. 2) [8].
a
60
1
45
ε' 30
2 15
3 0
b
10 1
ε" 5
0 3 10
10
ε" 5
0 β 10 20
2
4
f, Hz
10
5
β1
10 kHz
1
30
TGS NCC+TGS
1 kHz
4
40
ε'
50
60
2 β2
70
b 80
90
Fig. 2. The Cole-Cole plots for the single crystal TGS (1, 2) and composite NCC+TGS (3, 4) at room temperature.
3
10
3.9 kHz 6.3 kHz 3
10
6
The smaller values of dielectric permittivity in nanocomposites NCC+TGS in the entire range of studied temperatures are obviously related to the significant influence of chemical hydrogen bonds at boundaries of NCC and nanocrystals TGS, leading to difficulty of the repolarization of electric dipoles of TGS in the measuring field.
Fig. 1. Frequency dependences of the real (a) and the imaginary (b) parts of dielectric permittivity for the single crystal TGS (1), the composite NCC+TGS (2) and NCC (3) at room temperature.
273
a
60
3 50
ε'
The observed smearing of the dielectric permittivity maximum is obviously attributable to a nanochannel diameter dispersion in the initial NCC matrix and its nonuniform filling with TGS nanocrystals. The typical for the single crystal TGS Debye-like relaxation of dielectric permittivity is obviously described by the classical Cole-Cole equation [9]:
54 oC 50 oC 45 oC
2
40
ε * − ε∞ =
1 30
12
ε"
54 oC
3
ε * − ε ∞ lin = ε ∞ lin ( j ωτ
50 oC 45 oC
lin
1 4
kx + η x = 2 Ps E , 3
4
10
10
5
f, Hz
10
Fig. 3. Frequency dependences of the real (a) and the imaginary (b) parts of dielectric permittivity for the composite NCC+TGS at different temperatures.
10
10 kHz
ε" 5
β
0 10 10
20
ε'
40
1 5 .8 k H z
50
β
20
a
30 15.8 kH z
ε" 5 β
ε
20
ε'
50
60
60
4 kH z 1 kH z
45ºC
∞ lin
30
ε'
40
50 50
(4)
Thus the study of the dispersion of dielectric permittivity in the composite nanocrystalline cellulose – triglycine sulfate in the frequency range 103 – 106 Hz showed the presence of two relaxation sections. The Debye-like relaxation is observed at higher frequencies, and the linear dispersion – at lower frequencies due to respectively the reversible and irreversible domain-wall motion of the TGS crystallites introduced into the matrix of nanocrystalline cellulose. The most probable reason of the shift of the maximum "(f) to the range of lower frequencies as compared with the single crystal TGS is an increasing viscosity of the domain-wall motion in the composite.
4 kHz
40
( 3)
IV. CONCLUSIONS 5 4 ºC
5 0 ºC
0 10
0 10
30
b
ε" 5
10
η x = 2 Ps E .
1 5 .8 k H z
c
(2)
(k and – the quasielastic and viscous effective coefficients respectively, x and x – the displacement and velocity of DW, Ps – the spontaneous polarization, – the measuring electric field), and respectively the irreversible DW motion, that is described by formula:
6
10
) − α lin ,
where the parameters lin, lin, lin have the same meaning as in equation 1. The value of lin is determined from the ColeCole plots. The physical reason of these types of relaxation can be [13,14] reversible motion of domain walls (DW) in ferroelectric TGS, represented by the formula:
2
8
(1)
where = 0 – – the depth of dispersion, 0, – the low and high limits of the Debye-like relaxation region respectively, m – the relaxation time, – parameter of the relaxation time distribution. The linear dispersion laws are well described by the equation corresponding to the form of “universal law” [1012]:
20
b
Δε , 1 + ( jωτ m )1−α
ACKNOWLEDGMENT
60
Fig. 4. The Cole-Cole plots for the composite NCC+TGS at different temperatures.
274
The study was supported by the Russian Science Foundation, project N 14-12-00583.
properties of the composite based on nanocrystalline cellulose and triglycine sulfate,” Ferroelectrics, vol. 469, pp. 116 – 119, 2014. [7] H. T. Nguyen, S. D. Milovidova, A.S. Sidorkin and O.V. Rogazinskaya, “Dielectric properties of composites based on nanocrystalline cellulose with triglycine sulfate,” Physics of the Solid State, vol. 57, pp. 503 – 506, 2015. [8] V. Alexandru, Carmen Mindru and C. Berbecaru, “Dielectric relaxation of TGS crystal in the second order phase transition,” Digest Journal of Nanomaterials and Biostructures, 7, 1353 – 1364, 2012. [9] Y. M. Poplavko, “Physics of dielectrics,” Kiev: Vyshcha shkola., 1980. [10] A.K. Jonscher, “Universal relaxation law,” Nature (London), vol. 267, 1977. [11] A.K. Jonscher, “Dielectric Relaxation in Solids,” Chelsea Dielectric Press (London), 1983. [12] N. M. Galiyarova, “Slow relaxation of the polarization and characteristics of a low-frequency dielectric spectru, of triglycine sulfate in the region of its phase transition,” Physics of the Solid State, vol. 31, pp. 1977 - 1980, 1989. [13] N. M. Galiyarova, “Critical slowing down of relaxing domain walls and interfaces in phase transition vicinities,” Ferroelectrics, vol.170, pp. 111-121, 1995.
REFERENCES [1] O. V. Rogazinskaya, S. D. Milovidova, A. S. Sidorkin, N. G. Popravko, M. A. Bosykh and V. S. Enshina, “Dielectric Properties of Ferroelectric Composites with TGS Inclusions,” Ferroelectrics, vol. 397, pp.191- 197, 2010. [2] S. V. Baryshnikov, E. V. Charnaya, Yu. A. Shatskaya, A. Yu. Milinskiy, M. I. Samoilovich, D. Michel and C. Tien, “Effect of confined geometry on linear and nonlinear dielectric properties of triglycine sulfate near the phase transition,” Physics of the Solid State, vol. 53, pp. 1212-1215, 2011. [3] E. Rysiakiewicz-Pasek, R. Poprawski, J. Polanska, A. Sieradzki and E.B. Radojewska, “Ferroelectric phase transition in triglycine sulphateembedded into porous glasses,” Journal of Non-Crystalline Solids, vol. 351, pp. 2703-2709, 2005. [4] Yu. G. Baklagina, A. K. Khripunov, A. A. Tkachenko, V. V. Kopeikin, N. A. Matveeva, V. K. Lavrentev, V. K. Nilova, T. E. Sukhanova, R. Yu. Smyslov, I. S. Zanaveskina, V.V. Klechkovskaya and L. A. Feigin, “Sorption properties of gel films of bactetial cellulose,” Journal of Applied Chemistry, vol. 78, pp. 1176 – 1181, 2005. [5] A. K. Khripunov, A. A. Tkachenko, Yu. G. Baklagina, L. N. Borovikiva, V. K. Nilova, R. Yu. Smyslov, V.V. Klechkovskaya, N. A. Matveeva, A. Ya. Volkov, V. K. Lavrentev, M. E. Vylegzhanina, T. E. Sukhanova and V. V. Kopeikin, “Formation of a composite from Se0 nanoparticles stabilized with polyvinylpyrrolidone and Acetobacter xylinum cellulose gel films,” Journal of Applied Chemistry, vol. 80, pp. 1549 – 1557, 2007. [6] S. D. Milovidova, O.V. Rogazinskaya, A.S. Sidorkin, Nguyen Hoai Thuong, E.V. Grohotova and N.G. Popravko, “Dielectric
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