Electric conductivity studies of composites based on (Cu₁₋xAgx)₆PS₅I superionic conductors
The composites based on superionic (Cu₁₋xAgx)₆PS₅I solid solutions were prepared by mixing of microcrystalline powder with polyvinylacetate glue. The temperature and frequency behaviour of the total electric conductivity of composites within the frequency range 1.0*10⁶ –1.2*10⁹ Hz and temperatur...
Збережено в:
| Дата: | 2014 |
|---|---|
| Автори: | , , , , , , , |
| Формат: | Стаття |
| Мова: | English |
| Опубліковано: |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2014
|
| Назва видання: | Semiconductor Physics Quantum Electronics & Optoelectronics |
| Онлайн доступ: | http://dspace.nbuv.gov.ua/handle/123456789/118410 |
| Теги: |
Додати тег
Немає тегів, Будьте першим, хто поставить тег для цього запису!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Цитувати: | Electric conductivity studies of composites based on (Cu₁₋xAgx)₆PS₅I superionic conductors / I.P. Studenyak, R.Yu. Buchuk, A.V. Bendak, O.O. Yamkovy, E. Kazakevicius, T. Šalkus, A. Kežionis, A.F. Orliukas // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2014. — Т. 17, № 4. — С. 425-428. — Бібліогр.: 12 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
irk-123456789-118410 |
|---|---|
| record_format |
dspace |
| spelling |
irk-123456789-1184102017-05-31T03:03:46Z Electric conductivity studies of composites based on (Cu₁₋xAgx)₆PS₅I superionic conductors Studenyak, I.P. Buchuk, R.Yu. Bendak, A.V. Yamkovy, O.O. Kazakevicius, E. Šalkus, T. Kežionis, A. Orliukas, A.F. The composites based on superionic (Cu₁₋xAgx)₆PS₅I solid solutions were prepared by mixing of microcrystalline powder with polyvinylacetate glue. The temperature and frequency behaviour of the total electric conductivity of composites within the frequency range 1.0*10⁶ –1.2*10⁹ Hz and temperature range 300 to 420 K were investigated. The linear increase of the total electric conductivity with temperature increase was revealed, as well as the influence of Cu->Ag cation substitution on electrical properties of (Cu₁₋xAgx)₆PS₅I composites was studied. 2014 Article Electric conductivity studies of composites based on (Cu₁₋xAgx)₆PS₅I superionic conductors / I.P. Studenyak, R.Yu. Buchuk, A.V. Bendak, O.O. Yamkovy, E. Kazakevicius, T. Šalkus, A. Kežionis, A.F. Orliukas // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2014. — Т. 17, № 4. — С. 425-428. — Бібліогр.: 12 назв. — англ. 1560-8034 PACS 78.40.Ha, 77.80.Bh http://dspace.nbuv.gov.ua/handle/123456789/118410 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| description |
The composites based on superionic (Cu₁₋xAgx)₆PS₅I solid solutions were
prepared by mixing of microcrystalline powder with polyvinylacetate glue. The
temperature and frequency behaviour of the total electric conductivity of composites
within the frequency range 1.0*10⁶
–1.2*10⁹ Hz and temperature range 300 to 420 K were
investigated. The linear increase of the total electric conductivity with temperature
increase was revealed, as well as the influence of Cu->Ag cation substitution on
electrical properties of (Cu₁₋xAgx)₆PS₅I composites was studied. |
| format |
Article |
| author |
Studenyak, I.P. Buchuk, R.Yu. Bendak, A.V. Yamkovy, O.O. Kazakevicius, E. Šalkus, T. Kežionis, A. Orliukas, A.F. |
| spellingShingle |
Studenyak, I.P. Buchuk, R.Yu. Bendak, A.V. Yamkovy, O.O. Kazakevicius, E. Šalkus, T. Kežionis, A. Orliukas, A.F. Electric conductivity studies of composites based on (Cu₁₋xAgx)₆PS₅I superionic conductors Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Studenyak, I.P. Buchuk, R.Yu. Bendak, A.V. Yamkovy, O.O. Kazakevicius, E. Šalkus, T. Kežionis, A. Orliukas, A.F. |
| author_sort |
Studenyak, I.P. |
| title |
Electric conductivity studies of composites based on (Cu₁₋xAgx)₆PS₅I superionic conductors |
| title_short |
Electric conductivity studies of composites based on (Cu₁₋xAgx)₆PS₅I superionic conductors |
| title_full |
Electric conductivity studies of composites based on (Cu₁₋xAgx)₆PS₅I superionic conductors |
| title_fullStr |
Electric conductivity studies of composites based on (Cu₁₋xAgx)₆PS₅I superionic conductors |
| title_full_unstemmed |
Electric conductivity studies of composites based on (Cu₁₋xAgx)₆PS₅I superionic conductors |
| title_sort |
electric conductivity studies of composites based on (cu₁₋xagx)₆ps₅i superionic conductors |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2014 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/118410 |
| citation_txt |
Electric conductivity studies of composites based on (Cu₁₋xAgx)₆PS₅I superionic conductors / I.P. Studenyak, R.Yu. Buchuk, A.V. Bendak, O.O. Yamkovy, E. Kazakevicius, T. Šalkus, A. Kežionis, A.F. Orliukas // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2014. — Т. 17, № 4. — С. 425-428. — Бібліогр.: 12 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
AT studenyakip electricconductivitystudiesofcompositesbasedoncu1xagx6ps5isuperionicconductors AT buchukryu electricconductivitystudiesofcompositesbasedoncu1xagx6ps5isuperionicconductors AT bendakav electricconductivitystudiesofcompositesbasedoncu1xagx6ps5isuperionicconductors AT yamkovyoo electricconductivitystudiesofcompositesbasedoncu1xagx6ps5isuperionicconductors AT kazakeviciuse electricconductivitystudiesofcompositesbasedoncu1xagx6ps5isuperionicconductors AT salkust electricconductivitystudiesofcompositesbasedoncu1xagx6ps5isuperionicconductors AT kezionisa electricconductivitystudiesofcompositesbasedoncu1xagx6ps5isuperionicconductors AT orliukasaf electricconductivitystudiesofcompositesbasedoncu1xagx6ps5isuperionicconductors |
| first_indexed |
2025-07-08T13:55:32Z |
| last_indexed |
2025-07-08T13:55:32Z |
| _version_ |
1837087255825481728 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 425-428.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
425
PACS 78.40.Ha, 77.80.Bh
Electric conductivity studies of composites based
on (Cu1-xAgx)6PS5I superionic conductors
I.P. Studenyak1, R.Yu. Buchuk1, A.V. Bendak1, O.O. Yamkovy1,
E. Kazakevicius2, T. Šalkus2, A. Kežionis2, A.F. Orliukas2
1Uzhhorod National University,
3, Narodna Sq., 88000 Uzhhorod, Ukraine
E-mail: studenyak@dr.com
2Vilnius University, Faculty of Physics,
9, Saulėtekio al., LT-10222 Vilnius, Lithuania
Abstract. The composites based on superionic (Cu1–xAgx)6PS5I solid solutions were
prepared by mixing of microcrystalline powder with polyvinylacetate glue. The
temperature and frequency behaviour of the total electric conductivity of composites
within the frequency range 1.0106–1.2109 Hz and temperature range 300 to 420 K were
investigated. The linear increase of the total electric conductivity with temperature
increase was revealed, as well as the influence of CuAg cation substitution on
electrical properties of (Cu1–xAgx)6PS5I composites was studied.
Keywords: superionic conductor, composite, electric conductivity, cation substitution,
compositional behavior.
Manuscript received 15.04.14; revised version received 20.08.14; accepted for
publication 29.10.14; published online 10.11.14.
1. Introduction
Superionic conductors Cu6РS5I and Ag6PS5I belong to
the family of compounds with argyrodite structure [1, 2].
They are chemical and structural analogues (at room
temperature they crystallize in cubic system). Studying
the electrical properties of Cu6РS5I crystals shows that
they possess high value of electric conductivity at room
temperature, which is comparable with the conductivity
of the best superionic conductors [3, 4]. Thus, the
electrical conductivity of mono- and polycrystalline
superionic conductor Cu6PS5I is equal to 1.310–3 and
2.010–4 S/cm, while the electrical conductivity of
polycrystalline Ag6PS5I is equal to 7.410–4 S/cm [5].
Among argyrodite-type superionic conductors, the
most intensively studied is Cu6PS5I crystal. At low
temperatures, in Cu6PS5I crystal two phase transitions
(PTs) occur: structural second-order PT at TII =
(269±2) K, which is accompanied by the symmetry
change cFmF 3434 as well as superionic and
ferroelastic first-order PT at TI = (144±1) K accompanied
by the symmetry change CccF 34 [6, 7]. Optical
absorption edge studies of Cu6PS5I crystal have shown
the existence of bound and free excitons at high
absorption levels at temperatures below the first-order
PT, while in the superionic state the temperature
behaviour of the exponential parts of the absorption edge
is described by the empirical Urbach rule [8, 9]. Some
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 425-428.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
426
electrical, thermodynamic and optical properties of Ag-
containing argyrodite-type superionic conductors are
studied in Refs. [5, 10, 11].
Thus, the presence of high ionic conductivity in
superionic phase determines the prospects of practical
application of argyrodite-type superionic conductors as
electrochemical power sources and sensors. The aim of
this paper is to prepare and investigate the electric
conductivity of composites based on (Cu1–xAgx)6PS5I
superionic conductors.
2. Experimental
To synthesize the polycrystalline samples of the
Cu6PS5I–Ag6PS5I system, the powders of Cu6PS5I and
Ag6PS5I compounds were used. The maximal
temperature of synthesis was 580 °С, duration of the
process was 145 hours, cooling was carried out in the
mode of the eliminated stove. The composite samples
were obtained by mixing the microcrystalline powder,
the average size of particles in which was 50 m, with
polyvinylacetate glue. Mixing was carried out in the
mechanical way in wet medium at room temperature; the
microcrystalline powder and polyvinylacetate glue was
mixed in proportion 90 and 10 wt.%, respectively. After
mixing, the pellets of 8 mm in diameter and 0.2–2 mm
thick were pressed at 150 MPa from as-prepared viscous
samples. The pressed samples were dried at room
temperature for 15 hours.
Measurements of the complex electric conductivity
of (Cu1–xAgx)6PS5I composites were carried out within
the frequency range 1.0106–1.2109 Hz and at the
temperatures from 300 to 420 K by using the coaxial
impedance spectrometer [12].
3. Results and discussion
Frequency dependences of the real part of complex
conductivity for composites based on solid solutions
under investigation are shown in Fig. 1. In the studied
temperature and frequency ranges, two dispersion regions,
caused by the ion transport in the intercrystallite regions
and in the bulk of composite microcrystals, are observed.
These frequency and temperature dependences of
indicate that two types of relaxation processes caused by
ion transport in superionic composites take place. The
high frequency parts of the spectra correspond to
relaxation in the bulk, while the lower parts correspond to
grain boundary processes. Both dispersion areas are
shifted into the high-frequency range with the temperature
increase. The observed dispersions of relaxation type are
confirmed by the impedance frequency dependences
plotted in the complex plane. Typical impedance spectrum
consists of two semicircles superposition, which centers
lie below the real axis. Relaxation process in the bulk
leads to the high frequency arc, while the low-frequency
arc illustrates the relaxation process in the grain boundary
areas of the composites.
Fig. 1. Frequency dependences of the real part of complex
conductivity for composites based on solid solutions:
(Cu0.3Ag0.7)6PS5I (a), (Cu0.5Ag0.5)6PS5I (b), and
(Cu0.7Ag0.3)6PS5I (c) at various temperatures.
Shown in Fig. 2 are the temperature dependences
of the real part of complex conductivity for
composites based on (Cu1–xAgx)6PS5I solid solutions
measured at various frequencies. It was revealed that at
temperature increase the value increases linearly
according to the Arrhenius law:
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 425-428.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
427
kT
E
T
aexp0 , (1)
where ΔEa is the activation energy of total electrical
conductivity, σ0 – constant value, k – Boltzmann
constant, T – temperature. From T dependences, the
activation energy ΔEa for (Cu1–xAgx)6PS5I composites
was determined.
It should be noted that the above mentioned
frequency regions are observed as maxima on the spectra
of imaginary part of complex impedance Z (Fig. 3).
From the frequency position of the high-frequency peak
of Z the relaxation frequencies fb of the relaxation
process in the bulk of composites were determined. It
was shown that the temperature dependences of fb
(Fig. 4) are well described by the equation:
kT
E
ff b
b exp0 , (2)
where ΔEb is the activation energy of fb, f0 – attempt
frequency related to the lattice vibrations. The obtained
from Eq. (2) values of ΔEb as well as ΔEa for
(Cu1–xAgx)6PS5I composites are presented in Fig. 5. It was
shown that the activation energy of total conductivity ΔEa
and bulk conductivity ΔEb in the superionic phase with
increasing the silver atoms content in (Cu1–xAgx)6PS5I
composites nonlinearly increases in the compositional
range x =0…0.7, at x = 0.7 they reach maxima and then
nonlinearly decreases. Besides, the bulk activation energy
ΔEb is lower than ΔEa.
It should be noted that substitution of Cu atoms by
the Ag ones leads to a nonlinear decrease of the real part
of complex conductivity within the compositional
interval x = 0…0.6, at x = 0.6 the minimum on the
compositional dependence is observed, at x > 0.6 the
electric conductivity increases.
Fig. 2. Temperature dependences of the real part of complex
conductivity for (Cu1–xAgx)6PS5I composites at the
frequency 10 MHz: (Cu0.3Ag0.7)6PS5I (1), (Cu0.5Ag0.5)6PS5I (2)
and (Cu0.7Ag0.3)6PS5I (3).
Fig. 3. Frequency dependences of the imaginary part of
impedance Z for (Cu1–xAgx)6PS5I composites at various
temperatures: (Cu0.3Ag0.7)6PS5I (a), (Cu0.5Ag0.5)6PS5I (b), and
(Cu0.7Ag0.3)6PS5I (c).
Fig. 4. Temperature dependences of the relaxation frequency fb
for (Cu1–xAgx)6PS5I composites: (Cu0.1Ag0.9)6PS5I (1),
(Cu0.3Ag0.7)6PS5I (2), (Cu0.5Ag0.5)6PS5I (3) and
(Cu0.7Ag0.3)6PS5I (4).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 425-428.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
428
Fig. 5. Compositional dependences of the real part of complex
conductivity at the frequency 10 MHz (a) and activation
energy (b) of the total electric conductivity Ea (1) as well as
the bulk activation energy Eb (2) of (Cu1–xAgx)6PS5I
composites at the temperature T = 300 K.
4. Conclusions
Composites based on (Cu1–xAgx)6PS5I superionic
conductors were prepared by mixing the micro-
crystalline powder with polyvinylacetate glue. The
complex electrical conductivity of (Cu1–xAgx)6PS5I
composites was measured within the temperature range
300 to 420 K and frequency one from 1 MHz to
1.2 GHz. The results have shown that substitution of
Cu atoms by the Ag ones leads to a nonlinear, with
downward bowing, increase of the real part of complex
conductivity . It has been observed that with the
temperature growth the value increases linearly
according to the Arrhenius law. It has been revealed
that, with increasing the frequency, the conductivity
value increases. Moreover, two dispersion areas,
caused by the ion transport at the grain boundaries and
in the bulk, are observed. With the temperature, both
parts are shifted to the high frequency range due to the
thermally activated mechanism of the above mentioned
processes.
References
1. W.F. Kuhs, R. Nitsche, K. Scheunemann, Vapour
growth and lattice data of new compounds with
icosahedral structure of the type Cu6PS5Hal (Hal =
Cl, Br, I) // Mater. Res. Bull. 11, p. 1115-1124 (1976).
2. T. Nilges, A. Pfitzner, A structural differentiation of
quaternary copper argyrodites: Structure – property
relations of high temperature ion conductors // Z.
Kristallogr. 220, p. 281-294 (2005).
3. V.V. Panko, I.P. Studenyak, V.S. Dyordyay, Gy.Sh.
Kovacs, A.N. Boretc, Y.V. Voroshilov, Influence of
technological condition on optical properties of
Cu6PS5Hal crystals // Neorganicheskie Materialy,
24, p. 120-123 (1988), in Russian.
4. I.P. Studenyak, M. Kranjčec, Gy.Sh. Kovacs, I.D.
Desnica, V.V. Panko, V.Yu. Slivka, Influence of
compositional disorder on optical absorption
processes in Cu6P(S1–xSex)5I crystals // J. Mat. Res.
16, p. 1600-1608 (2001).
5. R.B. Beeken, J.J. Garbe, J.M. Gillis, N.R. Petersen,
B.W. Podoll, M.R. Stoneman, Electrical
conductivities of the Ag6PS5X and the Cu6PSe5X
(X = Br, I) argyrodites // J. Phys. Chem. Solids, 66,
p. 882-886 (2005).
6. I.P. Studenyak, V.O. Stefanovich, M. Kranjčec,
I.D. Desnica, Yu.M. Azhnyuk, Gy.Sh. Kovacs,
V.V. Panko, Raman scattering studies of
Cu6PS5Hal (Hal = Cl, Br, I) fast-ion conductors //
Solid State Ionics, 95, p. 221-225 (1997).
7. A. Gagor, A. Pietraszko, D. Kaynts, Diffusion
paths formation for Cu ions in superionic Cu6PS5I
single crystals studied in terms of structural phase
transition // J. Solid State Chem. 178, p. 3366-3375
(2005).
8. I.P. Studenyak, M. Kranjčec, Gy.S. Kovacs,
V.V. Panko, I.D. Desnica, A.G. Slivka, P.P. Guranich,
The effect of temperature and pressure on the optical
absorption edge in Cu6PS5X (X = Cl, Br, I) crystals //
J. Phys. Chem. Solids, 60, p. 1897-1904 (1999).
9. I.P. Studenyak, M. Kranjčec, M.V. Kurik, Urbach rule
and disordering processes in Cu6P(S1–xSex)5Br1–yIy
superionic conductors // J. Phys. Chem. Solids, 67,
p. 807-817 (2006).
10. S. Fiechter, E. Gmelin, Thermochemical data of
argyrodite-type ionic conductors: Cu6PS5Hal
(Hal = Cl, Br, I) // Thermochim. Acta, 85, p. 155-
158 (1985).
11. J. Shamir, S. Fiechter, and H. Wetzel, Raman
spectra of argyrodites, M6PS5X (M = Cu and Ag;
X = Cl, Br and I), and some related thiophosphates
// J. Raman Spectroscopy, 17, p. 217-219 (1986).
12. A.F. Orliukas, A. Kezionis, E. Kazakevicius,
Impedance spectroscopy of solid electrolytes in the
radio frequency range // Solid State Ionics, 176,
p. 2037-2043 (2005).
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 425-428.
PACS 78.40.Ha, 77.80.Bh
electric conductivity studies of composites based
on (Cu1-xAgx)6PS5I superionic conductors
I.P. Studenyak1, R.Yu. Buchuk1, A.V. Bendak1, O.O. Yamkovy1,
E. Kazakevicius2, T. Šalkus2, A. Kežionis2, A.F. Orliukas2
1Uzhhorod National University,
3, Narodna Sq., 88000 Uzhhorod, Ukraine
E-mail: studenyak@dr.com
2Vilnius University, Faculty of Physics,
9, Saulėtekio al., LT-10222 Vilnius, Lithuania
Abstract. The composites based on superionic (Cu1–xAgx)6PS5I solid solutions were prepared by mixing of microcrystalline powder with polyvinylacetate glue. The temperature and frequency behaviour of the total electric conductivity of composites within the frequency range 1.0(106–1.2(109 Hz and temperature range 300 to 420 K were investigated. The linear increase of the total electric conductivity with temperature increase was revealed, as well as the influence of Cu(Ag cation substitution on electrical properties of (Cu1–xAgx)6PS5I composites was studied.
Keywords: superionic conductor, composite, electric conductivity, cation substitution, compositional behavior.
Manuscript received 15.04.14; revised version received 20.08.14; accepted for publication 29.10.14; published online 10.11.14.
1. Introduction
Superionic conductors Cu6РS5I and Ag6PS5I belong to the family of compounds with argyrodite structure [1, 2]. They are chemical and structural analogues (at room temperature they crystallize in cubic system). Studying the electrical properties of Cu6РS5I crystals shows that they possess high value of electric conductivity at room temperature, which is comparable with the conductivity of the best superionic conductors [3, 4]. Thus, the electrical conductivity of mono- and polycrystalline superionic conductor Cu6PS5I is equal to 1.3(10–3 and 2.0(10–4 S/cm, while the electrical conductivity of polycrystalline Ag6PS5I is equal to 7.4(10–4 S/cm [5].
Among argyrodite-type superionic conductors, the most intensively studied is Cu6PS5I crystal. At low temperatures, in Cu6PS5I crystal two phase transitions (PTs) occur: structural second-order PT at TII = (269±2) K, which is accompanied by the symmetry change
c
F
m
F
3
4
3
4
®
as well as superionic and ferroelastic first-order PT at TI = (144±1) K accompanied by the symmetry change
Cc
c
F
®
3
4
[6, 7]. Optical absorption edge studies of Cu6PS5I crystal have shown the existence of bound and free excitons at high absorption levels at temperatures below the first-order PT, while in the superionic state the temperature behaviour of the exponential parts of the absorption edge is described by the empirical Urbach rule [8, 9]. Some electrical, thermodynamic and optical properties of Ag-containing argyrodite-type superionic conductors are studied in Refs. [5, 10, 11].
Thus, the presence of high ionic conductivity in superionic phase determines the prospects of practical application of argyrodite-type superionic conductors as electrochemical power sources and sensors. The aim of this paper is to prepare and investigate the electric conductivity of composites based on (Cu1–xAgx)6PS5I superionic conductors.
2. Experimental
To synthesize the polycrystalline samples of the Cu6PS5I–Ag6PS5I system, the powders of Cu6PS5I and Ag6PS5I compounds were used. The maximal temperature of synthesis was 580 °С, duration of the process was 145 hours, cooling was carried out in the mode of the eliminated stove. The composite samples were obtained by mixing the microcrystalline powder, the average size of particles in which was 50 (m, with polyvinylacetate glue. Mixing was carried out in the mechanical way in wet medium at room temperature; the microcrystalline powder and polyvinylacetate glue was mixed in proportion 90 and 10 wt.%, respectively. After mixing, the pellets of 8 mm in diameter and 0.2–2 mm thick were pressed at 150 MPa from as-prepared viscous samples. The pressed samples were dried at room temperature for 15 hours.
Measurements of the complex electric conductivity of (Cu1–xAgx)6PS5I composites were carried out within the frequency range 1.0(106–1.2(109 Hz and at the temperatures from 300 to 420 K by using the coaxial impedance spectrometer [12].
3. Results and discussion
Frequency dependences of the real part of complex conductivity
s
¢
for composites based on solid solutions under investigation are shown in Fig. 1. In the studied temperature and frequency ranges, two dispersion regions, caused by the ion transport in the intercrystallite regions and in the bulk of composite microcrystals, are observed. These frequency and temperature dependences of
s
¢
indicate that two types of relaxation processes caused by ion transport in superionic composites take place. The high frequency parts of the spectra correspond to relaxation in the bulk, while the lower parts correspond to grain boundary processes. Both dispersion areas are shifted into the high-frequency range with the temperature increase. The observed dispersions of relaxation type are confirmed by the impedance frequency dependences plotted in the complex plane. Typical impedance spectrum consists of two semicircles superposition, which centers lie below the real axis. Relaxation process in the bulk leads to the high frequency arc, while the low-frequency arc illustrates the relaxation process in the grain boundary areas of the composites.
Fig. 1. Frequency dependences of the real part of complex conductivity (( for composites based on solid solutions: (Cu0.3Ag0.7)6PS5I (a), (Cu0.5Ag0.5)6PS5I (b), and (Cu0.7Ag0.3)6PS5I (c) at various temperatures.
Shown in Fig. 2 are the temperature dependences of the real part of complex conductivity
s
¢
for composites based on (Cu1–xAgx)6PS5I solid solutions measured at various frequencies. It was revealed that at temperature increase the
s
¢
value increases linearly according to the Arrhenius law:
÷
ø
ö
ç
è
æ
D
-
s
=
s
¢
kT
E
T
a
exp
0
,
(1)
where ΔEa is the activation energy of total electrical conductivity, σ0 – constant value, k – Boltzmann constant, T – temperature. From
(
)
T
s
¢
dependences, the activation energy ΔEa for (Cu1–xAgx)6PS5I composites was determined.
It should be noted that the above mentioned frequency regions are observed as maxima on the spectra of imaginary part of complex impedance
Z
¢
¢
(Fig. 3). From the frequency position of the high-frequency peak of
Z
¢
¢
the relaxation frequencies fb of the relaxation process in the bulk of composites were determined. It was shown that the temperature dependences of fb (Fig. 4) are well described by the equation:
÷
ø
ö
ç
è
æ
D
-
=
kT
E
f
f
b
b
exp
0
,
(2)
where ΔEb is the activation energy of fb, f0 – attempt frequency related to the lattice vibrations. The obtained from Eq. (2) values of ΔEb as well as ΔEa for
(Cu1–xAgx)6PS5I composites are presented in Fig. 5. It was shown that the activation energy of total conductivity ΔEa and bulk conductivity ΔEb in the superionic phase with increasing the silver atoms content in (Cu1–xAgx)6PS5I composites nonlinearly increases in the compositional range x =0…0.7, at x = 0.7 they reach maxima and then nonlinearly decreases. Besides, the bulk activation energy ΔEb is lower than ΔEa.
It should be noted that substitution of Cu atoms by the Ag ones leads to a nonlinear decrease of the real part of complex conductivity
s
¢
within the compositional interval x = 0…0.6, at x = 0.6 the minimum on the compositional dependence is observed, at x > 0.6 the electric conductivity increases.
Fig. 2. Temperature dependences of the real part of complex conductivity
s
¢
for (Cu1–xAgx)6PS5I composites at the frequency 10 MHz: (Cu0.3Ag0.7)6PS5I (1), (Cu0.5Ag0.5)6PS5I (2) and (Cu0.7Ag0.3)6PS5I (3).
Fig. 3. Frequency dependences of the imaginary part of impedance
Z
¢
¢
for (Cu1–xAgx)6PS5I composites at various temperatures: (Cu0.3Ag0.7)6PS5I (a), (Cu0.5Ag0.5)6PS5I (b), and (Cu0.7Ag0.3)6PS5I (c).
Fig. 4. Temperature dependences of the relaxation frequency fb for (Cu1–xAgx)6PS5I composites: (Cu0.1Ag0.9)6PS5I (1), (Cu0.3Ag0.7)6PS5I (2), (Cu0.5Ag0.5)6PS5I (3) and (Cu0.7Ag0.3)6PS5I (4).
Fig. 5. Compositional dependences of the real part of complex conductivity (( at the frequency 10 MHz (a) and activation energy (b) of the total electric conductivity (Ea (1) as well as the bulk activation energy (Eb (2) of (Cu1–xAgx)6PS5I composites at the temperature T = 300 K.
4. Conclusions
Composites based on (Cu1–xAgx)6PS5I superionic conductors were prepared by mixing the micro-crystalline powder with polyvinylacetate glue. The complex electrical conductivity of (Cu1–xAgx)6PS5I composites was measured within the temperature range 300 to 420 K and frequency one from 1 MHz to 1.2 GHz. The results have shown that substitution of Cu atoms by the Ag ones leads to a nonlinear, with downward bowing, increase of the real part of complex conductivity
s
¢
. It has been observed that with the temperature growth the
s
¢
value increases linearly according to the Arrhenius law. It has been revealed that, with increasing the frequency, the conductivity value increases. Moreover, two dispersion areas, caused by the ion transport at the grain boundaries and in the bulk, are observed. With the temperature, both parts are shifted to the high frequency range due to the thermally activated mechanism of the above mentioned processes.
References
1.
W.F. Kuhs, R. Nitsche, K. Scheunemann, Vapour growth and lattice data of new compounds with icosahedral structure of the type Cu6PS5Hal (Hal = Cl, Br, I) // Mater. Res. Bull. 11, p. 1115-1124 (1976).
2.
T. Nilges, A. Pfitzner, A structural differentiation of quaternary copper argyrodites: Structure – property relations of high temperature ion conductors // Z. Kristallogr. 220, p. 281-294 (2005).
3.
V.V. Panko, I.P. Studenyak, V.S. Dyordyay, Gy.Sh. Kovacs, A.N. Boretc, Y.V. Voroshilov, Influence of technological condition on optical properties of Cu6PS5Hal crystals // Neorganicheskie Materialy, 24, p. 120-123 (1988), in Russian.
4.
I.P. Studenyak, M. Kranjčec, Gy.Sh. Kovacs, I.D. Desnica, V.V. Panko, V.Yu. Slivka, Influence of compositional disorder on optical absorption processes in Cu6P(S1–xSex)5I crystals // J. Mat. Res. 16, p. 1600-1608 (2001).
5.
R.B. Beeken, J.J. Garbe, J.M. Gillis, N.R. Petersen, B.W. Podoll, M.R. Stoneman, Electrical conductivities of the Ag6PS5X and the Cu6PSe5X (X = Br, I) argyrodites // J. Phys. Chem. Solids, 66, p. 882-886 (2005).
6.
I.P. Studenyak, V.O. Stefanovich, M. Kranjčec, I.D. Desnica, Yu.M. Azhnyuk, Gy.Sh. Kovacs, V.V. Panko, Raman scattering studies of Cu6PS5Hal (Hal = Cl, Br, I) fast-ion conductors // Solid State Ionics, 95, p. 221-225 (1997).
7.
A. Gagor, A. Pietraszko, D. Kaynts, Diffusion paths formation for Cu ions in superionic Cu6PS5I single crystals studied in terms of structural phase transition // J. Solid State Chem. 178, p. 3366-3375 (2005).
8.
I.P. Studenyak, M. Kranjčec, Gy.S. Kovacs, V.V. Panko, I.D. Desnica, A.G. Slivka, P.P. Guranich, The effect of temperature and pressure on the optical absorption edge in Cu6PS5X (X = Cl, Br, I) crystals // J. Phys. Chem. Solids, 60, p. 1897-1904 (1999).
9.
I.P. Studenyak, M. Kranjčec, M.V. Kurik, Urbach rule and disordering processes in Cu6P(S1–xSex)5Br1–yIy superionic conductors // J. Phys. Chem. Solids, 67, p. 807-817 (2006).
10.
S. Fiechter, E. Gmelin, Thermochemical data of argyrodite-type ionic conductors: Cu6PS5Hal (Hal = Cl, Br, I) // Thermochim. Acta, 85, p. 155-158 (1985).
11.
J. Shamir, S. Fiechter, and H. Wetzel, Raman spectra of argyrodites, M6PS5X (M = Cu and Ag; X = Cl, Br and I), and some related thiophosphates // J. Raman Spectroscopy, 17, p. 217-219 (1986).
12. A.F. Orliukas, A. Kezionis, E. Kazakevicius, Impedance spectroscopy of solid electrolytes in the radio frequency range // Solid State Ionics, 176, p. 2037-2043 (2005).
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
425
_1477996899.unknown
_1477999551.unknown
_1477999552.unknown
_1477996926.unknown
_1477996947.unknown
_1477997028.unknown
_1477996944.unknown
_1477996907.unknown
_1477996778.unknown
_1477996883.unknown
_1477996888.unknown
_1477996870.unknown
_1477498678.unknown
_1477930849.unknown
_1477157844.unknown
_1477163073.unknown
|