Transport properties and polarization phenomena in intercalated Ag x HfSe 2 compounds

TL;DR: In this paper, the electrical properties of intercalated Ag and HfSe2 compounds have been investigated for the first time using various current electrodes, which make it possible to pass either the electron current or the ion current across the sample.

Abstract: The electrical properties of intercalated Ag x HfSe2 compounds (x = 0.1, 0.2) have been investigated for the first time. Investigations have been performed using various current electrodes, which make it possible to pass either the electron current or the ion current across the sample. Polarization effects, which indicate the self-consistent migration of charge carriers in the samples, have been found for the samples at room temperature. Based on the characteristic features of polarization decay, coefficients of conjugated chemical diffusion have been evaluated.

Summary

1. INTRODUCTION

• It is known that a large series of compounds con taining copper or silver ions, which possess high mobility, form a whole class of superionic conductors [1–3].
• Some dichalcogenides of transition metals, which are intercalated by lithium ions, are already used as electrodes for chemical cur rent sources [8].
• In contrast to silver and copper chalcogenides, where structural disorder, which leads to a high ion mobility, occurs at elevated temperatures as a result of phase transformations [1, 2], such state in intercalated com pounds can be formed by the change of the concentra tion of the intercalated element at lower temperatures.
• During the intercalation of 3d atoms of transition metals into the TX2 structure, intercalated atoms form the bonds with the atoms of adjoining layers of the parent matrix.

2. SAMPLE PREPARATION AND EXPERIMENTAL TECHNIQUE

• Parent hafnium diselenide was synthesized by the method of solid phase reactions from initial elements in evacuated quartz ampules as it was performed pre viously for the synthesis of titanium dichalcogenides and intercalated materials on their base [9–11].
• Thus prepared HfSe2 was used for the subsequent synthesis of intercalated AgxHfSe2 samples (x = 0.1, 0.2) by the same procedure.
• The X ray diffraction attestation of these samples and the subsequent determination of structural characteristics was performed using a Bruker D8 Advance diffractometer in CuK α radiation.
• The second circuit was the Ag/Ag4RbI5/AgxHfSe2/Ag4RbI5/Ag electrochemical cell, which makes it possible to pass the ion current across the sample and to block the electron transfer.
• To measure the potential differ ence, the authors used electronic measuring probes connected to sample ends and neutral with respect to silver.

3. RESULTS

• The results of X ray diffraction attestation of the samples showed that the structure of all obtained materials corresponded to the CdI2 structural type.
• One can see that it also exhibits the ten dency to the change of the character of the tempera ture dependence from activation (with a very low acti vation energy) to metallic.the authors.
• Figure 2 shows the current–voltage characteristic for the Ag0.1HfSe2 sample during the cyclic (0 Umax 0 –Umax 0) variation of the applied potential difference.
• When passing the electric current across the sam ples, its decrease with time was found, which corre sponds to an increase in effective resistance of the samples at a constant applied potential difference and indicates the appearance of barriers preventing the electron transfer.
• Only the conjugated chemical diffusion coefficients (CCDC) can be found from the presented experimental data.

4. CONCLUSIONS

• The possibility to implement rather high mobility of silver ions in intercalated compounds PHYSICS OF THE SOLID STATE Vol. 55 No. 1 2013 TRANSPORT PROPERTIES AND POLARIZATION.
• PHENOMENA 25 based on hafnium diselenide is investigated for the first time.
• Polarization phenomena associated with the self consistent migration character of silver ions and electrons under applying the external electric field and after its switching off are found for the studied sam ples.
• The established character of time dependences of the potential difference between various sections of the samples corresponds qualitatively to the analysis of the potential distribution in mixed electron–ion con ductors for combinations of current electrodes and measuring probes used by us [24].
• Thus, the obtained data indicate that intercalated AgxHfSe2 compounds posses rather high mobility of silver ions and can be considered as materials with mixed electron–ion conductivity, which is essential, for example, for the development of electrode materi als.

Figures

Fig. 2. Current–voltage characteristics of the Ag0.1HfSe2 sample at temperatures of 290 and 90 K (in inset).

Fig. 1. Temperature dependences of the resistivity of the AgxHfSe2 samples: (a) x = 0.1 and (b) 0.2. The same dependence for the AgxHfSe2 sample at x = 0 is shown in the inset.

Fig. 4. Curves of (1) establishing polarization under pass ing the ion current and (2) its decay after switching off the current for the Ag0.2HfSe2 sample. The measuring circuit is shown in the inset, F = Ag4RbI5.

Fig. 3. Polarization decay curves for the Ag0.1HfSe2 sample after passing the electron current in two opposite direc tions.

Full text

ISSN 10637834, Physics of the Solid State, 2013, Vol. 55, No. 1, pp. 21–25. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © V.G. Pleshchev, N.V. Selezneva, N.V. Baranov, 2013, published in Fizika Tverdogo Tela, 2013, Vol. 55, No. 1, pp. 14–18.
21
1. INTRODUCTION
It is known that a large series of compounds con
taining copper or silver ions, which possess high
mobility, form a whole class of superionic conductors
[1–3]. The nature of this phenomenon is associated
with the existence of the intrinsic structural disorder in
them, at which the copper and silver ions are weakly
bonded with a crystalline skeleton, and a large number
of equivalent sites separated by insignificant potential
barriers exist in them. A similar situation can be imple
mented for intercalated dichalcogenides of transition
metals
TX
2
(
T
is the transition metal of Group IV or V,
and
X
is the chalcogen). The main feature of their
crystalline structure is the presence of a weak van der
Waals bond between
X
–
T
–
X
threelayer blocks, which
allows us to intercalate atoms of other elements into
the interlayer spacing [4–7]. Some dichalcogenides of
transition metals, which are intercalated by lithium
ions, are already used as electrodes for chemical cur
rent sources [8]. Intercalated atoms can occupy only
some equivalent sites in the van der Waals gap depend
ing on their concentration in the
TX
2
structure. In
contrast to silver and copper chalcogenides, where
structural disorder, which leads to a high ion mobility,
occurs at elevated temperatures as a result of phase
transformations [1, 2], such state in intercalated com
pounds can be formed by the change of the concentra
tion of the intercalated element at lower temperatures.
The structure and physical properties of interca
lated
M
x
TX
2
compounds after the intercalation of
M
atoms can differ considerably from those characteris
tic of the initial compounds [7, 9, 10]. During the
intercalation of 3
d
atoms of transition metals into the
TX
2
structure, intercalated atoms form the bonds with
the atoms of adjoining layers of the parent matrix. The
nature of such bonds depends on the sort of 3
d
atoms
and the chalcogen type in the
TX
2
matrix. Particularly,
as it was established for intercalated titanium dichal
cogenides, the degree of covalence of the bonds
increases as the atomic number of chalcogen increases
in a series TiS
2
–TiSe
2
–TiTe
2
[9, 11]. The preferen
tially covalent character of bonds in
M
x
Ti
X
2
systems
manifests itself in a decrease in unit cell parameter
c
during intercalation as compared with the initial com
pounds [9–11]. As opposed to this fact, copper and
silver atoms, due to a spherical symmetry of 4
s
and 5
s
states, correspondingly, do not possess the tendency to
establishment of such bonds, and their intercalation
leads to an increase in parameter
c
as a rule. This was
particularly shown in calculations of the distribution
of the electron density in the Cu
x
TiS
2
compounds
[12]; it also follows from the data on the determination
of concentration dependences of unit cell parameters
in the Cu
x
TiS
2
, Cu
x
TiSe
2
, and Cu
x
HfSe
2
compounds
[13–15].
There are several articles devoted to the investigation
of kinetic properties of compounds intercalated with
silver (Ag
x
TX
2
), where the data on high mobility of silver
ions in these compounds were obtained along with the
characteristics of the electron transfer [16–19]. Physi
cal properties of intercalated compounds based on
hafnium dichalcogenides are much less studied; how
ever, there are the articles devoted to the synthesis and
investigation of silvercontaining phases such as the
Ag
2
HfS
3
and Ag
4
HfS
8
compounds, which also have the
layered structure and possess rather high ion conductiv
SEMICONDUCTORS
Transport Properties and Polarization Phenomena
in Intercalated Ag
x
HfSe
2
Compounds
V. G. Pleshchev
a
, N. V. Selezneva
a
, and N. V. Baranov
a
,
b
a
Institute of Natural Science, Ural Federal University,
pr. Lenina 51, Yekaterinburg, 620083 Russia
* email: Valery.Pleschov@usu.ru
b
Institute of Metal Physics, Ural Branch of the Russian Academy of Sciences,
ul. S. Kovalevskoi 18, Yekaterinburg, 620990 Russia
Received April 23, 2012
Abstract
—The electrical properties of intercalated Ag
x
HfSe
2
compounds (
x
= 0.1, 0.2) have been investi
gated for the first time. Investigations have been performed using various current electrodes, which make it
possible to pass either the electron current or the ion current across the sample. Polarization effects, which
indicate the selfconsistent migration of charge carriers in the samples, have been found for the samples at
room temperature. Based on the characteristic features of polarization decay, coefficients of conjugated
chemical diffusion have been evaluated.
DOI:
10.1134/S1063783413010253

22
PHYSICS OF THE SOLID STATE
Vol. 55
No. 1
2013
PLESHCHEV et al.
ity. For example, it is noted that the ion conductivity in
the Ag
2
HfS
3
compound is ~10
–3
(
Ω
cm)
–1
at room tem
perature, while the transfer number of silver ions is
close to unity [20, 21].
The data available in publications show that the
further studies of silvercontaining transition metal
chalcogenide compounds are of doubtless interest. In
this connection, our study is devoted to the investiga
tion of chargetransfer phenomena in hafnium dise
lenide intercalated by silver ions.
2. SAMPLE PREPARATION
AND EXPERIMENTAL TECHNIQUE
Parent hafnium diselenide was synthesized by the
method of solidphase reactions from initial elements
in evacuated quartz ampules as it was performed pre
viously for the synthesis of titanium dichalcogenides
and intercalated materials on their base [9–11]. Thus
prepared HfSe
2
was used for the subsequent synthesis
of intercalated Ag
x
HfSe
2
samples (
x
= 0.1, 0.2) by the
same procedure. The Xray diffraction attestation of
these samples and the subsequent determination of
structural characteristics was performed using a
Bruker D8 Advance diffractometer in Cu
K
α
radiation.
To investigate the charge transfer in materials
with the electron–ionic conductivity, several meth
ods differing by various combinations of current
electrodes and measuring probes is used. We used
two circuits in this work. The first one is a standard
fourprobe circuit with electron current leads block
ing the transfer of silver ions and electron measuring
probes. It allowed us to determine the characteristics
of the electron charge transfer. Measurements using
this circuit were performed for compacted and
annealed cylindrical samples 4.2 mm in diameter
and 8 mm in length. The second circuit was the
Ag/Ag
4
RbI
5
/Ag
x
HfSe
2
/Ag
4
RbI
5
/Ag electrochemical
cell, which makes it possible to pass the ion current
across the sample and to block the electron transfer.
The Ag
4
RbI
5
compound is one of better ion conduc
tors, which can be used at room temperature, when its
ion conductivity is ~0.3 (
Ω
cm)
–1
[2]. The sample was
a pellet 10 mm in diameter and 2 mm thick in this case.
The Ag
4
RbI
5
pellets had the same diameter and a
thickness of 1.8 mm. To measure the potential differ
ence, we used electronic measuring probes connected
to sample ends and neutral with respect to silver. Elec
tric resistance was measured in a temperature range of
10–300 K, and polarization phenomena were investi
gated at room temperature.
3. RESULTS
The results of Xray diffraction attestation of the
samples showed that the structure of all obtained
materials corresponded to the CdI
2
structural type. It
was established by the phase analysis that the samples
were almost singlephased. Only a small (no larger
than 5%) amount of the HfO
2
phase was found as a
foreign impurity apparently introduced with metal
hafnium when it was milled during the sample prepa
ration. The data obtained by the Xray diffraction
analysis for the parent hafnium diselenide and
Ag
x
HfSe
2
samples are tabulated. Unit cell parameters
of parent hafnium diselenide correspond to these
found previously in [4, 5], while the data for interca
lated samples (similarly to the Cu
x
HfSe
2
system [15])
indicate an increase in parameters during intercalating
the samples.
The results of studying the temperature depen
dences of electrical resistance
ρ
(
T
) of the Ag
x
HfSe
2
samples performed using the first circuit give the infor
mation on the features of the electron transfer (Fig. 1).
An increase in the silver content in the samples leads
to a decrease in electrical resistance, which, as it was
mentioned for Ag
0.33
TiS
2
[16], can be associated with
the transfer of 5
s
electrons of silver into 5
d
band of
hafnium. Measurements of thermopower for both
samples indicate the electron type of charge carriers. It
is seen from Fig. 1 that the character of dependence
ρ
(
T
) for the Ag
0.1
HfSe
2
sample changes from the acti
vation at low temperatures to metallic in the interme
diate region (120–250 K). Above 250 K, its electrical
resistance starts to decrease again. The activation
energy of conductivity for the Ag
0.1
HfSe
2
sample in a
lowtemperature region is very low (~10
–4
eV).
Despite the fact that electrical conductivity of the
3002001000
T
, K
65
60
55
50
45
7.5
7.0
6.5
ρ
,
Ω
cm
ρ
,
Ω
cm
(a)
(b)
Ag
0.1
HfSe
2
Ag
0.2
HfSe
2
300250200150
T
, K
HfSe
2
10
5
0
ρ
, k
Ω
m
Fig. 1.
Temperature dependences of the resistivity of the
Ag
x
HfSe
2
samples: (a)
x
= 0.1 and (b) 0.2. The same
dependence for the Ag
x
HfSe
2
sample at
x
= 0 is shown in
the inset.

PHYSICS OF THE SOLID STATE
Vol. 55
No. 1
2013
TRANSPORT PROPERTIES AND POLARIZATION PHENOMENA 23
Ag
0.2
HfSe
2
samples varies rather weakly as the temper
ature increases, we can see that it also exhibits the ten
dency to the change of the character of the tempera
ture dependence from activation (with a very low acti
vation energy) to metallic. Taking into account that
the temperature regions of the transition from the acti
vation dependence to the metallic one almost coincide
for both samples, we can assume the general nature of
such a transition. Since the activation energy of con
duction in a lowtemperature region is very low, this
region is associated probably with the electron excita
tion from impurity centers into the conduction band,
and scattering of charge carriers in this band at thermal
oscillations prevails starting from a certain tempera
ture. In view of low excitation energy of charge carri
ers, the change of the character of the
ρ
(
T
) depen
dence in a region of 120–250 K can correspond to the
depletion of impurities known for semiconductors. To
clarify if the transition from the metallictype depen
dence to the activation dependence at temperatures
above 250 K is the consequence of the change in the
atomic structure, we performed Xray diffraction
investigations of the sample with
x
= 0.1 at 290 and
113 K. These investigations had not revealed the qual
itative structural changes excluding an increase in unit
cell parameters with an increase in temperature (see
table). It follows from here that this transition is not
associated with structural transformations. When
measuring electrical resistance of intercalated sam
ples, we noted that the roomtemperature magnitude
of the electric current passing across the samples was
unstable and varied as the polarity of the supplied volt
age changed. It is possible that the interaction of the
electron and ion charge carriers starts to manifest itself
in this temperature region.
In order to investigate the chargetransfer phe
nomena in more detail, we measured the current–
voltage characteristics of the samples. It was found
that they are nonlinear at room temperature and
exhibit the hysteresis as the direction of the applied
field changes. Figure 2 shows the current–voltage
characteristic for the Ag
0.1
HfSe
2
sample during the
cyclic (0
U
max
0 –
U
max
0) variation of
the applied potential difference. As the temperature
decreases, the shape of the current–voltage character
istic approaches the linear one, while the hysteresis
almost disappears. Based on this fact, we can assume
the occurrence of certain relaxation processes, which
are associated with migration of silver ions under the
applied electric field. Since this migration should have
the activation character, it is suppressed at low tem
peratures, and the current–voltage characteristic
becomes ohmic.
When passing the electric current across the sam
ples, its decrease with time was found, which corre
sponds to an increase in effective resistance of the
samples at a constant applied potential difference and
indicates the appearance of barriers preventing the
electron transfer. Such processes are characteristic of
the materials which manifest dielectric properties,
including ionic conductors, and, as was mentioned in
[22, 23], they can be associated with the polarization
and the formation of a bulk charge near blocking elec
trodes.
With switching off the current after the establish
ment of the steady polarization, the measured poten
tial difference abruptly decreased to a certain residual
value
U
res
(0) and then tended to zero with time. Fig
ure 3 shows the dependences
U
res
(
t
) for the Ag
0.1
HfSe
2
sample after passing the current in two opposite direc
tions. The difference of electric potentials measured
experimentally reflects the difference of electrochem
ical potentials of electrons, which is in turn governed
by the difference in the concentration of silver ions
over the sample length, which appears during the
polarization. The observed dependences
U
res
(
t
) can be
considered as a consequence of the polarization decay,
when the chargecarrier concentration over the sam
ple length is leveled as a result of diffusion processes.
The difference of electrochemical potentials of elec
trons also disappears in this case. It should be specially
noted that the sign of the residual potential difference
coincides with the sign of the potential difference dur
ing passing the current. Such characteristic signs of the
polarization decay for this measuring circuit (electron
electrodes and electron probes) were established by
the theoretical analysis of the potential distribution in
Unit cell parameters
a
and
c
of the Ag
x
HfSe
2
samples found
at room temperature (the values found at
T
= 113 K are
shown in parentheses)
xa
, Å
c
, Å
0 3.7428 6.1553
0.1 3.7444 (3.7442) 6.1563 (6.1548)
0.2 3.7449 6.1567
80
40
0
−
40
−
80
I
, mA
12840
−
4
−
8
U
, V
1680
−
8
−
16
U
, V
30
0
−
30
−
60
T
= 90 K
I
, mA
T
= 290 K
Fig. 2.
Current–voltage characteristics of the Ag
0.1
HfSe
2
sample at temperatures of 290 and 90 K (in inset).

24
PHYSICS OF THE SOLID STATE
Vol. 55
No. 1
2013
PLESHCHEV et al.
mixed electron–ion conductors [24] and verified
experimentally for silver chalcogenides [24, 25]. When
analyzing the presented dependences, it was shown
that they follow the exponential dependence of the
U
res
(
t
) ~ exp(–
t
/
τ
) type, which corresponds to the
solution of the second Fick law (inset in Fig. 3), where
τ
is the relaxation time, which is 80 s for the made eval
uation.
Polarization phenomena were also investigated
using the second circuit, in which the charge transfer
could be performed only by silver ions. The phenom
ena indicating the appearing polarization in the sam
ples were also observed during passing the ion current
across the cell. Time dependences of the potential dif
ference during passing the current for the Ag
0.2
HfSe
2
sample, which correspond to the process of establish
ment of polarization (curve
1
) and describing the
polarization decay after switching off the current
(curve
2
) are also shown in Fig. 4. It is seen that after
switching off the current, the potential difference
between the measuring probes changed the sign (in
contrast to similar measurements performed using the
first circuit upon passing the electron current) and
tended to zero with time. These data also qualitatively
correspond to the results obtained for the case of ion
current electrodes and electron measuring probes
[24]. The curves of polarization establishment and
decay, which are presented in Fig. 4, were described
satisfactorily by the exponential function. In this case,
characteristic relaxation times
τ
for both processes
were approximately the same and equal to 180–200 s.
When analyzing these results, we should take into
account the fact that two types of charged particles,
namely, electrons and silver ions, the migration of
which is selfconsistent, are present in the samples
under study. In this case, only the conjugated chemical
diffusion coefficients (CCDC) can be found from the
presented experimental data. We determined the
CCDC values using the expression following from the
solution of the second Fick equation:
D
* =
L
2
/
π
2
t
,
where
L
is the diffusion length and
t
is the time of
reaching the steady state. This time was determined
from the polarization decay curves (Figs. 3, 4) and
constitutes approximately 500 s for the Ag
0.1
HfSe
2
sample and 1300 s for the Ag
0.2
HfSe
2
sample. When
calculating diffusion coefficients, we found the values
of 1.2
×
10
–5
cm
2
/s for Ag
0.1
HfSe
2
and 3.0
×
10
–6
cm
2
/s
for Ag
0.2
HfSe
2
. According to the conceptions devel
oped for materials with mixed conductivity [26, 27],
the values of CCDC reflect the migration of both sorts
of diffusing particles and can be represented in a form
D
* =
z
e
D
i
+
z
i
D
e
, where
z
e
and
z
i
are the transfer num
bers for electrons and ions, respectively; and
D
i
and
D
e
are the partial diffusion coefficients for ions and elec
trons, respectively. We can isolate the ion diffusion
coefficient from the presented expression only if
z
e
~ 1.
Since we had not found the data on the investigation of
transfer phenomena in compounds under consider
ation, it seems impossible to do this based on the
results found in our study only.
The fact seems to be unusual that a smaller diffusion
coefficient is found for the sample with a higher silver
concentration. However, allowing for the expression
describing the CCDC, this situation can be realistic
with a certain variation in the ratio of transfer numbers
from one hand and partial diffusion coefficients from
the other hand. One possible cause is that as the silver
concentration increases, the fraction of free sites in the
van der Waals gap per one silver ion decreases, which
can lead to a decrease in their mobility.
4. CONCLUSIONS
In this study, the possibility to implement rather
high mobility of silver ions in intercalated compounds
2
–4
0
–2
U
res
, mV
−
6
−
8
−
10
−
12
ln
U
res
[V]
10008006004002000
t
, s
4503001500
t
, s
Fig. 3.
Polarization decay curves for the Ag
0.1
HfSe
2
sample
after passing the electron current in two opposite direc
tions.
100806040200
t
, min
3
–1
2
1
0
U
, mV
1
2
Ag
FF
AgAg
0.2
HfSe
2
Fig. 4.
Curves of (
1
) establishing polarization under pass
ing the ion current and (
2
) its decay after switching off the
current for the Ag
0.2
HfSe
2
sample. The measuring circuit
is shown in the inset,
F
= Ag
4
RbI
5
.

PHYSICS OF THE SOLID STATE
Vol. 55
No. 1
2013
TRANSPORT PROPERTIES AND POLARIZATION PHENOMENA 25
based on hafnium diselenide is investigated for the first
time. Polarization phenomena associated with the
selfconsistent migration character of silver ions and
electrons under applying the external electric field and
after its switching off are found for the studied sam
ples. The established character of time dependences of
the potential difference between various sections of
the samples corresponds qualitatively to the analysis of
the potential distribution in mixed electron–ion con
ductors for combinations of current electrodes and
measuring probes used by us [24].
Thus, the obtained data indicate that intercalated
Ag
x
HfSe
2
compounds posses rather high mobility of
silver ions and can be considered as materials with
mixed electron–ion conductivity, which is essential,
for example, for the development of electrode materi
als. To determine diffusion coefficients of silver ions
and the magnitude of ion conductivity directly, addi
tional experiments should be performed.
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Translated by N. Korovin

Frequently asked questions

Q1. What are the contributions in this paper?

In this paper, the electrical properties of intercalated AgxHfSe2 compounds ( x = 0.1, 0.2 ) have been investi gated for the first time. 

Q2. What are the future works in this paper?

In this study, the possibility to implement rather high mobility of silver ions in intercalated compounds PHYSICS OF THE SOLID STATE Vol. 55 No. 1 2013 TRANSPORT PROPERTIES AND POLARIZATION The established character of time dependences of the potential difference between various sections of the samples corresponds qualitatively to the analysis of the potential distribution in mixed electron–ion con ductors for combinations of current electrodes and measuring probes used by us [ 24 ]. Thus, the obtained data indicate that intercalated AgxHfSe2 compounds posses rather high mobility of silver ions and can be considered as materials with mixed electron–ion conductivity, which is essential, for example, for the development of electrode materi als. 

Q3. What is the main feature of the crystalline structure of transition metals?

The main feature of their crystalline structure is the presence of a weak van der Waals bond between X–T–X three layer blocks, which allows us to intercalate atoms of other elements into the interlayer spacing [4–7]. 

Q4. What is the effect of the change in the character of the depen dence?

In view of low excitation energy of charge carri ers, the change of the character of the ρ(T) depen dence in a region of 120–250 K can correspond to the depletion of impurities known for semiconductors. 

Q5. What is the ion conducive value of the Ag4RbI5 compound?

The Ag4RbI5 compound is one of better ion conduc tors, which can be used at room temperature, when its ion conductivity is ~0.3 (Ω cm)–1 [2]. 

Q6. What is the nature of the intercalated dichalcogenides?

Some dichalcogenides of transition metals, which are intercalated by lithium ions, are already used as electrodes for chemical cur rent sources [8]. 

Q7. How did the authors determine the CCDC values for Ag0?

The authors determined theCCDC values using the expression following from the solution of the second Fick equation: D* = L2/π2t, where L is the diffusion length and t is the time of reaching the steady state. 

Q8. What is the effect of the polarization decay on the sam ple?

The observed dependences Ures(t) can be considered as a consequence of the polarization decay, when the charge carrier concentration over the sam ple length is leveled as a result of diffusion processes. 

Q9. How can the authors determine diffusion coefficients of silver ions?

To determine diffusion coefficients of silver ions and the magnitude of ion conductivity directly, addi tional experiments should be performed. 

Q10. What is the first circuit used in this work?

The first one is a standardfour probe circuit with electron current leads block ing the transfer of silver ions and electron measuring probes. 

Q11. What is the CCDC value for Ag0?

According to the conceptions devel oped for materials with mixed conductivity [26, 27], the values of CCDC reflect the migration of both sorts of diffusing particles and can be represented in a form D* = zeDi + ziDe, where ze and zi are the transfer num bers for electrons and ions, respectively; and Di and De are the partial diffusion coefficients for ions and elec trons, respectively. 

Q12. What is the nature of the intrinsic structural disorder in transition metals?

The nature of this phenomenon is associated with the existence of the intrinsic structural disorder in them, at which the copper and silver ions are weakly bonded with a crystalline skeleton, and a large number of equivalent sites separated by insignificant potential barriers exist in them. 

Q13. What is the effect of the change in the atomic structure of the sample?

To clarify if the transition from the metallic type depen dence to the activation dependence at temperatures above 250 K is the consequence of the change in the atomic structure, the authors performed X ray diffraction investigations of the sample with x = 0.1 at 290 and 113 K. 

Q14. What is the reason for the high mobility of silver ions in intercalated AgxH?

the obtained data indicate that intercalated AgxHfSe2 compounds posses rather high mobility of silver ions and can be considered as materials with mixed electron–ion conductivity, which is essential, for example, for the development of electrode materi als. 

Q15. What was the X ray diffraction attestation of these samples?

The X ray diffraction attestation of these samples and the subsequent determination of structural characteristics was performed using a Bruker D8 Advance diffractometer in CuKα radiation. 

Q16. What is the difference between the two measuring probes?

4. It is seen that after switching off the current, the potential difference between the measuring probes changed the sign (in contrast to similar measurements performed using the first circuit upon passing the electron current) and tended to zero with time.