Influence of Li-TCNQ impurities on dielectric properties of planar-oriented nematic liquid crystal
The dielectric properties of planar-oriented nematic liquid crystal E25M with Li-TCNQ impurities have been investigated within the frequency range 10–1…106 Hz and temperatures 298…343 K. The concentration of impurities varied between 0 and 0.1 wt.%. It has been shown that the presence of a small imp...
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| Опубліковано в: : | Semiconductor Physics Quantum Electronics & Optoelectronics |
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| Дата: | 2018 |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2018
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| Цитувати: | Influence of Li-TCNQ impurities on dielectric properties of planar-oriented nematic liquid crystal / V.E. Vovk, O.V. Kovalchuk, T.M. Kovalchuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2018. — Т. 21, № 4. — С. 397-401. — Бібліогр.: 8 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860479630254800896 |
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| author | Vovk, V.E. Kovalchuk, O.V. Kovalchuk, T.M. |
| author_facet | Vovk, V.E. Kovalchuk, O.V. Kovalchuk, T.M. |
| citation_txt | Influence of Li-TCNQ impurities on dielectric properties of planar-oriented nematic liquid crystal / V.E. Vovk, O.V. Kovalchuk, T.M. Kovalchuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2018. — Т. 21, № 4. — С. 397-401. — Бібліогр.: 8 назв. — англ. |
| collection | DSpace DC |
| container_title | Semiconductor Physics Quantum Electronics & Optoelectronics |
| description | The dielectric properties of planar-oriented nematic liquid crystal E25M with Li-TCNQ impurities have been investigated within the frequency range 10–1…106 Hz and temperatures 298…343 K. The concentration of impurities varied between 0 and 0.1 wt.%. It has been shown that the presence of a small impurity of Li-TCNQ in liquid crystal increases electrical conductivity, influences the value of the conductivity activation energy in the nematic phase, and practically does not change the activation energy in the isotropic phase. The times of dielectric relaxation τ for the low-frequency part of the spectrum of complex dielectric constant components have been estimated. It has been shown that, within the frame of existence of the liquid crystal phase, the temperature dependence of τ–1 linearly depends on the inverse value of the temperature in the Arrhenius coordinates and agrees well with the temperature dependence of conductivity.
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| first_indexed | 2026-03-23T18:47:19Z |
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ISSN 1560-8034, 1605-6582 (On-line), SPQEO, 2018. V. 21, N 4. P. 397-401.
© 2018, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
397
Hetero- and low-dimensional structures
Influence of Li-TCNQ impurities on dielectric properties
of planar-oriented nematic liquid crystal
V.E. Vovk
1
, O.V. Kovalchuk
1,2,3
, T.M. Kovalchuk
4
1
Institute of Physics, National Academy of Sciences of Ukraine, 46, prospect Nauky, 03680 Kyiv, Ukraine
2
Kyiv National University of Technologies and Design, 2, Nemirovich-Danchenko str., 01011 Kyiv, Ukraine
E-mail: akoval@knutd.com.ua
3
National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”
37, prospect Peremohy, 03056 Kyiv, Ukraine
4
V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, 41, prospect Nauky, 03680 Kyiv, Ukraine
Abstract. The dielectric properties of planar-oriented nematic liquid crystal E25M with
Li-TCNQ impurities have been investigated within the frequency range 10
–1
…10
6
Hz and
temperatures 298…343 K. The concentration of impurities varied between 0 and 0.1 wt.%.
It has been shown that the presence of a small impurity of Li-TCNQ in liquid crystal
increases electrical conductivity, influences on the value of the conductivity activation
energy in the nematic phase and practically does not change the activation energy in the
isotropic phase. The times of dielectric relaxation τ for the low-frequency part of the
spectrum of complex dielectric constant components have been estimated. It has been
shown that, within the frame of existence of the liquid crystal phase, the temperature
dependence of τ
–1
linearly depends on the inverse value of the temperature in the Arrhenius
coordinates and is well agreed with the temperature dependence of conductivity.
Keywords: dielectric spectroscopy, nematic liquid crystal, Li-TCNQ impurity, activation
energy.
doi: https://doi.org/10.15407/spqeo21.04.397
PACS 77.84.Nh
Manuscript received 23.10.18; revised version received 19.11.18; accepted for publication
29.11.18; published online 03.12.18.
1. Introduction
As it is known, currently liquid crystals are widely used
in display technology. In more than 80% of the displays
made in the whole world, the active element is liquid
crystals. Many publications imply that liquid crystals can
also be used in devices other than device displays. To do
this, one need to somehow change their properties.
Conductivity is one of the important parameters of
liquid crystals. Since the main effect of the display
operation is change in orientation of molecules under the
influence of electric field, in the display technology
developers try to use liquid crystals with low electrical
conductivity. However, an increase in the conductivity of
liquid crystals can significantly to expand opportunities
of practical application of these substances. Therefore,
the search for impurities, with the help of which one can
effectively change conductivity, as well as other
electrical parameters of liquid crystal, is an important
scientific and applied task.
The purpose of this work was to study the
possibility of increasing the conductivity of the liquid
crystal mixture E25M by introducing Li-TCNQ
impurities [1-5]. Earlier [6], we showed that introduction
of the modified C60 impurity into E25M liquid crystal
leads to an increase in the conductivity of liquid crystal.
Since Li-TCNQ impurity, in contrast to the C60 one,
absorbs light better in the visible spectral region, then, in
addition to changing the electrical properties, when this
impurity is introduced into the liquid crystal, the optical
properties of liquid crystal must also change.
2. Materials and methods
For research purposes, we used the nematic liquid crystal
E25M prepared in BDH Chemicals Ltd. For this liquid
crystal, the phase transition from the isotropic phase to
the nematic one is observed at the temperature TIN =
331 K. The studied mixture of liquid crystal with
Li-TCNQ was prepared using direct introduction into
SPQEO, 2018. V. 21, N 4. P. 397-401.
Vovk V.E., Kovalchuk O.V., Kovalchuk T.M. Influence of Li-TCNQ impurities on dielectric properties …
398
10
-1
10
0
10
1
10
2
10
3
10
4
10
5
10
6
10
0
10
1
10
2
10
3
f, Hz
ε'
1
2
Fig. 1. Frequency dependences of the real component of the
complex dielectric permittivity ε' for E25M (1) and E25M +
0.1 wt.% Li-TCNQ (2) at the temperature 298 K (nematic phase
of liquid crystal).
liquid crystal at room temperature T = 293 K. Then the
mixture was stirred mechanically with a magnetic stirrer,
and then it was placed into the ultrasonic disperser
UZDN-2T at the frequency of 22 kHz for 30 min. As the
experiment showed, the solubility of Li-TCNQ in the
liquid crystal is not sufficiently high, therefore, studies
were performed for low concentrations of impurities
within the range 0.003 to 0.1 wt.%.
To investigate dielectric properties, we used
sandwich type glass cells with the thickness 25 µm that
were set by the Teflon substrates. The orientation of the
molecules of liquid crystal in the cells was provided by
depositing the polyamide orienting layer and further
rubbing. The orientation of liquid crystal in the cell was
controlled using the crossed polarizers. The studies have
shown that in all the samples planar orientation of
molecules was provided technologically clearly (long
axes of elliptical molecules were oriented in one
direction parallel to the substrate plane).
For better control of the cell thickness (as well as
the distance between the electrodes), before filling with
liquid crystal, the capacitance of the empty cell C0 was
measured. To avoid edge effects, the cell electrodes were
separated into two parts: the internal (measuring) and
outer ones. During the measurement, the outer electrode
was grounded. The role of the electrode was played by
In2O3 deposited on the glass. The separation of the
electrode into two parts was carried out by etching.
All measurements were performed within the
temperature range 293 to 343 K. The temperature
stabilization error during measurements did not exceed
0.5 K. The frequency dependences of C and R were
measured using the oscilloscopic method [7]. The
alternating voltage of the triangular shape with the
amplitude U0 = 0.25 V within the frequency range ƒ =
10
–1
…10
6
Hz was applied to the sample.
3. Experimental results and discussion
As already noted, Li-TCNQ has a low solubility in the
liquid crystal E25M. In order to avoid the processes of
precipitation of Li-TCNQ molecules on the electrode
surface, we filled up the prepared E25M + Li-TCNQ
mixture into the cell to be examined already before the
measurement itself. In this case, the mixture was heated
to the temperature 343 K (to increase the solubility) and
then, being based on the capillary effect, was filled into
the heated cell. During filling the cell, the liquid crystal
remained in the isotropic phase. Measurements for
various temperatures were performed when the samples
were cooled.
Fig. 1 shows the frequency dependences of the real
component of the complex permittivity ε' for the planar-
oriented nematic liquid crystal E25M (1) and for E25M +
0.1 wt.% Li-TCNQ mixture (2) at the temperature T =
298 K.
As it follows from the analysis of the data shown in
Fig. 1, the entire spectrum of ε' can be separated into
three sections. First, we analyze the spectrum for pure
liquid crystal (curve 1). For the frequencies ƒ < 10 Hz, a
sharp increase of the ε' value with decreasing the
frequency is observed. This low-frequency dispersion is
caused by a change in orientation of molecules in the
near-electrode sections of the liquid crystal under action
of an electric field within the angles corresponding to
fluctuations of the order parameter of the liquid crystal
(several degrees). In order to this process to be effective,
almost all the electric field is applied to a thin (about ten
nanometers) of the near-electrode layer. Since this
process is due to redistribution of the electric field in the
sample, its parameters depend on the conductivity of the
bulk part of the sample.
As shown in Fig. 1, embedding the Li-TCNQ
impurity most significantly affects the parameters of the
low-frequency region of the spectrum for the real
component of complex permittivity. As it will be shown
further, this occurs precisely by increasing the
conductivity of the liquid crystal when introducing the
Li-TCNQ impurity.
From Fig. 1 (curve 1) it follows that, within the
frequency range 10 to 10
5
Hz, the ε' value does not depend
on the frequency. This section of the spectrum corresponds
to the frequencies, at which the electric field is applied to
the bulk part of the sample. In this case, the ε' value
corresponds to the passport data of the liquid crystal. It is
important to note that introduction of Li-TCNQ impurity
leads to a slight decrease in the ε' value, as follows from
the analysis of Fig. 1. Since the liquid crystal mixture
E25M studied by us has a positive value of anisotropy of
the dielectric permittivity (the dielectric permittivity at the
homeotropic orientation is greater than that at the planar
orientation), this effect can be explained by the additional
to the orienting surfaces action ordering of the molecules
under the action of the impurity. Such an effect may be
both bulk (due to interaction of impurity molecules
SPQEO, 2018. V. 21, N 4. P. 397-401.
Vovk V.E., Kovalchuk O.V., Kovalchuk T.M. Influence of Li-TCNQ impurities on dielectric properties …
399
10
-1
10
0
10
1
10
2
10
3
10
4
10
5
10
6
10
-1
10
0
10
1
10
2
10
3
2
f, Hz
ε"
1
Fig. 2. Frequency dependences of the imaginary component of
the complex dielectric permittivity ε'' for E25M (1) and E25M
+ 0.1 wt.% Li-TCNQ (2) at a temperature of 298 K (the
nematic phase of liquid crystal).
with the liquid crystal ones) and the surface one due to
improvement of orienting action of the electrodes
because of adsorption of the impurity molecules on their
surface. We believe that improving the orienting ability
of electrodes in consequence of adsorption of Li-TCNQ
impurity molecules at the electrodes is the main
mechanism for reducing the ε' value.
The third section of the ε' dispersion begins from
the frequencies ƒ > 10
5
Hz. For this section, a decrease in
the ε' value is typical. As it is known from the theoretical
notions about polarization of liquids, the ε' dispersion for
these frequencies is due to the fact that the molecules do
not have time equal to the change in the voltage of the
measuring signal from zero to the amplitude value to turn
to a certain angle. Since this type of dipole polarization is
characteristic for all liquids, we will not separately
consider its analysis and influence of impurities on the
parameters of this process.
Fig. 2 shows the frequency dependence for the
imaginary component of the complex dielectric
permittivity ε" for E25M (curve 1) and E25M + 0.1 wt.%
Li-TCNQ (curve 2). From the analysis of these data, it
follows that, like to the case of ε', the dielectric spectrum
can be separated into three sections. First, let’s analyze
the second (if the increase in the frequency is taken as the
basis of separation) section of the dielectric spectrum. In
contrast to the spectral dependence of ε' (in the second
section of the dielectric spectrum, the ε' value did not
depend on the frequency) for the second section of the
spectral dependence of ε", as it is evident from Fig. 2, the
inverse proportional dependence of ε" on ƒ is typical.
This dependence of ε" on ƒ corresponds to the condition
that the sample resistance does not depend on the
frequency. In this case, when knowing the resistance
determined in the second section of the frequency
dependence of ε", we can determine the sample
conductivity on the alternating current σAC. To calculate
the conductivity, we used the following relation:
2.9 3.0 3.1 3.2 3.3 3.4
10
-8
10
-7
10
-6
10
-5
10
-4
4
3
2
σ
A
C
,
O
h
m
−
1
m
−
1
10
3
/T, K
−1
1
Fig. 3. Temperature dependence of the conductivity of nematic
liquid crystal E25M with various concentrations of the
Li-TCNQ impurity: 0 (1), 0.003 (2), 0.01 (3), 0.1 (4) wt.%.
ωεεσ ′′= vAC , (1)
where εv is the dielectric constant, and ω = 2πf is the
cyclic frequency.
After determing the magnitude of conductivity, it
was important to analyze its dependence on temperature.
The temperature dependences of conductivity for E25M
with various concentrations of Li-TCNQ impurity are
plotted in Fig. 3.
As it follows from Fig. 3, within the temperature
interval of the existence of a mesophase of liquid crystal,
the conductivity linearly depends on the inverse
temperature in the Arrhenius coordinates. That is, the
temperature dependence of the conductivity can be
described by the relation:
kT
E
AC e
σ
0σσ
∆
−
= , (2)
where σ0 is the conductivity at infinitely high
temperature, ∆Еσ – activation energy for the temperature
dependence of conductivity, and k – Boltzmann’s
constant.
As it follows from the analysis of Fig. 3, the slope
of curve for the temperature dependence of conductivity
in the isotropic phase does not depend on the presence of
an impurity. According to the equation (2), it indicates
that the presence of an impurity in the isotropic phase
does not effect on the activation energy of the
conductivity ∆Еσ. According to our estimations, the ∆Еσ
value for an isotropic phase of liquid crystal is
(0.22 ± 0.06) eV, regardless of the impurity
concentration. This value coincides with our data
obtained for the E25M mixture with modified fullerene
in the work [6].
Also, as it follows from the analysis of Fig. 3, for
the nematic phase the slope of curves in the temperature
dependence for the conductivity changes somewhat
depending on the content of Li-TCNQ in liquid crystal.
SPQEO, 2018. V. 21, N 4. P. 397-401.
Vovk V.E., Kovalchuk O.V., Kovalchuk T.M. Influence of Li-TCNQ impurities on dielectric properties …
400
According to our estimations, for E25M the ∆Еσ value in
the nematic phase is (0.55 ± 0.06) eV, and for
E25M + 0.1 wt.% Li-TCNQ ∆Еσ = (0.3 ± 0.06) eV. In
our previous studies, for the E25M mixture with
modified fullerene [6], we did not observe the effect of
the impurity on the activation energy of conductivity in
the nematic phase at planar orientation of molecules. In
the work [6], the effect of impurity on the activation
energy of conductivity was observed at the homotropic
orientation of molecules. We can assume that this
difference between the results is caused by different
interaction of the modified fullerene and Li-TCNQ with
the molecules of liquid crystal.
After analyzing the second section of the dielectric
spectrum, we will consider the first section in more
detail. As it was noted above, the relaxation process in
the first section of the spectrum of components of the
complex dielectric constant is caused by fluctuation of
dipolar molecules in the near-electrode region within the
angles equal to fluctuations of the order parameter. Our
analysis shows that this relaxation process corresponds to
the Debye dispersion and is described by the relation
tiω+
ε−ε
ε=ε ∞
∞
∗
1
0
, (3)
where ε* is the dielectric permittivity, ε0 and ε∞ are
dielectric permittivity for the frequencies f = 0 and f = ∞,
respectively, and τ is the relaxation time.
The performed by us analysis of the relaxation
process caused by rotation of the dipolar molecules in the
near-electrode area of the sample shows that the
relaxation time should be inversely proportional to the
conductivity of the sample. Therefore, to confirm the
assumption about the nature of relaxation process in the
first section of the dielectric spectrum shown in Figs. 1
and 2, we have analyzed the temperature dependence of
inverse relaxation time 1/τ. The temperature dependence
of 1/τ of liquid crystal E25M with various concentrations
of Li-TCNQ impurity is shown in Fig. 4.
2.9 3.0 3.1 3.2 3.3 3.4
10
-1
10
0
10
1
10
2
10
3
10
4
4
3
2
NI
τ−
1
,
s−
1
10
3
/T, K
−1
1
Fig. 4. Temperature dependences of inverse relaxation time τ–1
for nematic liquid crystal E25M with various concentrations of
Li-TCNQ impurity: 0 (1), 0.003 (2), 0.01 (3), 0.1 (4) wt.%.
If we compare the temperature dependences of the
conductivity σАС and inverse relaxation time τ
–1
(Figs. 3
and 4), one can note rather good correlation between
these dependences. This reaffirms our assumption that
the relaxation process in the first section of the dielectric
spectrum is caused by the change in orientation of the
molecular dipoles in the near-electrode region of the
spectrum due to oscillations within the angles
corresponding to fluctuations of the order parameter.
Let’s briefly analyze the third section of the
dielectric spectrum for ƒ > 10
5
Hz. Our analysis shows
that the third section can also be described by the relation
(3). It is known from the theory that this relaxation
process is due to the fact that the molecular dipoles do
not have time to turn to a certain angle during the change
in the voltage of the measuring signal. Since, as noted
above, this process is inherent to any liquids and has
been studied in detail, we did not analyze it.
4. Conclusions
1. Dielectric spectra of components of complex
dielectric permittivity for the mixtures of planar-oriented
nematic liquid crystal E25M with a low concentration of
Li-TCNQ impurities at the temperatures 298 to 343 K
and within the frequency range 10
–1
…10
6
Hz have been
investigated. It has been shown that the whole dielectric
spectrum can be separated into three sections. For low
frequencies (in the case of E25M without impurities it is
for ƒ < 10 Hz), the essential dependence of the dielectric
permittivity on the frequency is caused by redistribution
of the electric field to provide current in the near-
electrode sections of the sample as a result of oscillation
of the molecular dipoles within the angles equal to
fluctuations of the order parameter. At the medium
frequencies, the electric field is applied to the whole
volume. It allows us to find the conductivity and
dielectric permittivity of the sample. The third section of
the dielectric spectrum begins at the frequencies
ƒ > 10
5
Hz. The third section, like to the first one, of the
dielectric spectra is described by the Debye equation and
is caused by the fact that during the time of change in
voltage of the measuring signal the molecule dipoles do
not have time to turn to a certain angle.
2. The conductivity σАС of both pure liquid crystal
E25M and that with Li-TCNQ impurities is linearly
dependent on the inverse temperature value in the
Arrhenius coordinates ( ( )1ln −σ TAC ). It has been shown
that the activation energy of conductivity in the isotropic
phase of liquid crystal does not depend on the
concentration of the impurity and is equal to Еσ =
(0.22 ± 0.06) eV. In the case of the nematic phase, the
activation energy of the conductivity decreases with
increasing the concentration of the impurity from Еσ =
(0.55 ± 0.06) eV for pure E25M to Еσ = (0.3 ± 0.06) eV
for E25M + 0.1 wt.% Li-TCNQ.
3. The times of dielectric relaxation τ for the
relaxation process caused by rotation of the molecular
dipoles in the near-electrode regions of the samples
within the angles corresponding to fluctuations of the
SPQEO, 2018. V. 21, N 4. P. 397-401.
Vovk V.E., Kovalchuk O.V., Kovalchuk T.M. Influence of Li-TCNQ impurities on dielectric properties …
401
order parameter have been estimated. It has been shown
that the temperature dependence of inverse relaxation
time τ
–1
has a linear form in the Arrhenius coordinates
and is well agreed with the temperature dependence of
the conductivity σAС. This fact confirms the proposed
mechanism of the low-frequency relaxation process.
References
1. Afify H.H., Abdel-Kerim F.M., Aly H.F., Shabaka
A.A. The electrical conductivity of some alkali- and
divalent transition metal TCNQ salts. Z.
Naturfotschung. 1978. 33a. P. 344–346.
2. Chen Y., Manzhos S. A computational study of
lithium interaction with tetracyanoethylene (TCNE)
and tetracyaniquinodimethane (TCNQ) molecules.
Phys. Chem. Chem. Phys. 2016. 18. P. 1470–1477.
3. Fadly M. Effect of light and temperature on the
electrical resistivity of PMMA doped with charge
transfer complexes. Polymer. plast. technol. Eng.
1995. 34. P. 17–28.
4. Khanna S.K., Ehrenfreud E., Rybachewski E.F.,
Etemad S. Magnetic resonance studies in LiTCNQ.
AIP Conference Proc. 1973. 10. P. 1509–1513.
5. Li Z.-J., Li Z.-R., Wang F.-F., Ma F., Huang X.-R.
The charge transfer anion-radical alkali-metal salts
M
+
TCNQ
–
(M = Li, Na, K): The structures and
static hyperpolarizabilities. Chem. Phys. Lett. 2009.
468. P. 319–324.
6. Vovk V.E., Koval’chuk A.V., Lebovka N. Impact
of homeotropic and planar alignment of liquid
crystalline medium on the structure and dielectric
properties of modified fullerene mC60 + E25M
mixtures. Liquid Crystal. 2012. 39. P. 77–86.
7. Twarowski A.J., Albrecht A.C. Depletion layer in
organic films: Low frequency measurements in
polycrystalline tetracene J. Chem. Phys. 1979. 20.
P. 2255–2261.
8. Gornitska O.P., Koval’chuk A.V., Koval’chuk
T.M., Kopcansky P., Timko M., Zavisiva V.,
Komeracka M., Tomasovicova N., Jadsyn J.,
Studenyak I.P. Dielectric properties of nematic
liquid crystal with Fe2O3 nanoparticles in direct
magnetic field. SPQEO. 2009. 12. P. 309–314.
Authors and CV
Vladislav E. Vovk, Junior Researcher
at the Molecular Photoelectronics
Department, Institute of Physics, NAS
of Ukraine. Authored 4 articles, 4
theses. The area of scientific interests
is liquid crystals, dielectric
spectroscopy, heterostructures, solar
cells, molecular photoelectronics,
self-organization of molecular systems.
Oleksandr V. Kovalchuk, Doctor of
Physical and Mathematical Sciences,
senior scientific researcher at the
Molecular Photoelectronics
Department, Institute of Physics, NAS
of Ukraine; Head of the Department
of Physics, professor at the Kyiv
National University of Technologies
and Design and National Technical University of
Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”.
Authored over 150 articles, 8 patents. The area of
scientific interests is dielectric spectroscopy of liquid
crystals and composites.
E-mail: akoval@knutd.com.ua
Tetiana M. Kovalchuk, scientific
researcher at V. Lashkaryov Institute
of Semiconductor Physics, NAS of
Ukraine. Authored over 20 articles.
The area of scientific interests is
dielectric spectroscopy of liquid
crystals and composites.
|
| id | nasplib_isofts_kiev_ua-123456789-215320 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1560-8034 |
| language | English |
| last_indexed | 2026-03-23T18:47:19Z |
| publishDate | 2018 |
| publisher | Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| record_format | dspace |
| spelling | Vovk, V.E. Kovalchuk, O.V. Kovalchuk, T.M. 2026-03-12T08:53:37Z 2018 Influence of Li-TCNQ impurities on dielectric properties of planar-oriented nematic liquid crystal / V.E. Vovk, O.V. Kovalchuk, T.M. Kovalchuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2018. — Т. 21, № 4. — С. 397-401. — Бібліогр.: 8 назв. — англ. 1560-8034 PACS: 77.84.Nh https://nasplib.isofts.kiev.ua/handle/123456789/215320 https://doi.org/10.15407/spqeo21.04.397 The dielectric properties of planar-oriented nematic liquid crystal E25M with Li-TCNQ impurities have been investigated within the frequency range 10–1…106 Hz and temperatures 298…343 K. The concentration of impurities varied between 0 and 0.1 wt.%. It has been shown that the presence of a small impurity of Li-TCNQ in liquid crystal increases electrical conductivity, influences the value of the conductivity activation energy in the nematic phase, and practically does not change the activation energy in the isotropic phase. The times of dielectric relaxation τ for the low-frequency part of the spectrum of complex dielectric constant components have been estimated. It has been shown that, within the frame of existence of the liquid crystal phase, the temperature dependence of τ–1 linearly depends on the inverse value of the temperature in the Arrhenius coordinates and agrees well with the temperature dependence of conductivity. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics Hetero- and low-dimensional structures Influence of Li-TCNQ impurities on dielectric properties of planar-oriented nematic liquid crystal Article published earlier |
| spellingShingle | Influence of Li-TCNQ impurities on dielectric properties of planar-oriented nematic liquid crystal Vovk, V.E. Kovalchuk, O.V. Kovalchuk, T.M. Hetero- and low-dimensional structures |
| title | Influence of Li-TCNQ impurities on dielectric properties of planar-oriented nematic liquid crystal |
| title_full | Influence of Li-TCNQ impurities on dielectric properties of planar-oriented nematic liquid crystal |
| title_fullStr | Influence of Li-TCNQ impurities on dielectric properties of planar-oriented nematic liquid crystal |
| title_full_unstemmed | Influence of Li-TCNQ impurities on dielectric properties of planar-oriented nematic liquid crystal |
| title_short | Influence of Li-TCNQ impurities on dielectric properties of planar-oriented nematic liquid crystal |
| title_sort | influence of li-tcnq impurities on dielectric properties of planar-oriented nematic liquid crystal |
| topic | Hetero- and low-dimensional structures |
| topic_facet | Hetero- and low-dimensional structures |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/215320 |
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