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In the present study, Cu2SnSe3/x% Ni (x = 0, 1, 2 and 3 wt%) composite thermoelectric were synthesized using solid-state reaction followed by sintering in the mid-temperature range 300–570 K. XRD studies revealed that the samples have a diamond cubic structure with the F4¯3m space group. Scanning Electron Microscopy indicates that the synthesized samples possess homogeneous surfaces with fewer pores. The sample with 3% Ni exhibits an approximately eight-fold increase in electrical conductivity than the pure sample at 307 K. However, the addition of Ni decreased the Seebeck coefficient, resulting in a lower overall power factor (PF) for the composites. The highest PF of ∼420 μW/mK², was observed in the pristine sample at 570 K. Although Ni addition improves electrical properties, it negatively impacts the overall thermoelectric performance due to the significant reduction in Seebeck coefficient, thereby lowering the overall power factor.
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Mater. Res. Express 11 (2024)076302 https://doi.org/10.1088/2053-1591/ad6534
PAPER
Incorporation of Ni in Cu
2
SnSe
3
: An insight into the reduction in
electrical resistivity
Rohith Jagan, Twinkle Gurung, Deepika Shanubhogue U, G Poojitha, Poornesh P
and Ashok Rao
Department of Physics, Manipal Institute of Technology, Manipal Academy of Higher Education Manipal, 576104, Karnataka, India
Authors to whom any correspondence should be addressed.
E-mail: poornesh.p@manipal.edu,poorneshp@gmail.com and a.rao@manipal.edu
Keywords: thermoelectrics, metal composites, carrier concentration, chalcogenides, power factor
Abstract
In the present study, Cu
2
SnSe
3
/x%Ni(x=0, 1, 2 and 3 wt%)composite thermoelectric were
synthesized using solid-state reaction followed by sintering in the mid-temperature range 300570 K.
XRD studies revealed that the samples have a diamond cubic structure with the
¯
F
m43
space group.
Scanning Electron Microscopy indicates that the synthesized samples possess homogeneous surfaces
with fewer pores. The sample with 3% Ni exhibits an approximately eight-fold increase in electrical
conductivity than the pure sample at 307 K. However, the addition of Ni decreased the Seebeck
coefcient, resulting in a lower overall power factor (PF)for the composites. The highest PF of 420
μW/mK
2
, was observed in the pristine sample at 570 K. Although Ni addition improves electrical
properties, it negatively impacts the overall thermoelectric performance due to the signicant
reduction in Seebeck coefcient, thereby lowering the overall power factor.
1. Introduction
The severity of the global energy crisis and environmental pollution is rising along with the development of
modern society [1]. Rising global warming and the energy crisis remain among the worlds most challenging
issues. As a result, sustainable and renewable energy sources have drawn broad enthusiasm from the scientic
society [2]. Based on the well-known Seebeck and Peltier effects, thermoelectric (TE)technology provides a
pollution-free means of directly converting thermal gradient into electrical energy [3,4]. The maximum energy
conversion efciency is primarily determined by the gure of merit (ZT)of the TE materials, which can be
expressed as,
()
s
kk
=
+
ZT ST 1
el
2
where
T
is the absolute temperature, keand klare the electronic and lattice thermal conductivity,
s
is the
electrical conductivity, and Sis the Seebeck coefcient [5]. Decoupling these parameters (
S,
s
,
keand kl)for
simultaneous optimization of electrical and thermal transport properties is challenging due to their inherent
interdependencies [6]. High TE performance materials are crucial for TE applications, but their environmental
friendliness and producibility should also be considered. Many modern materials, including half-Heusler [7],
SnTe [8], PbTe [9], GeTe [10], and CuInTe
2
[11]have been reported to exhibit superior TE performances at
intermediate temperatures [12]. Unfortunately, these materials are expensive and hazardous and they require
complex synthesis processes, which pose problems for their widespread industrial applications [13].
Among several thermoelectric materials Cu
2
SnSe
3
is a Cu-based ternary compound having diamond-like
structure. It has emerged as a useful TE material because of its lower thermal conductivity, tuneable electrical
conductivity, and high specic heat [5,14]. Additionally, this class of materials is an economical and
environmentally benecial option for TE applications due to its advantages of low toxicity and high elemental
abundance [15]. The Cu
2
SnSe
3
structure forms an electrically conductive framework because of the Cu-Se bond
network, and it is possible to modify the electrical conductivity of Cu
2
SnSe
3
by partially substituting at the Sn site
OPEN ACCESS
RECEIVED
8 May 2024
REVISED
19 June 2024
ACCEPTED FOR PUBLICATION
18 July 2024
PUBLISHED
29 July 2024
Original content from this
work may be used under
the terms of the Creative
Commons Attribution 4.0
licence.
Any further distribution of
this work must maintain
attribution to the
author(s)and the title of
the work, journal citation
and DOI.
© 2024 The Author(s). Published by IOP Publishing Ltd
[2]. Studies have shown that the properties of thermoelectric materials can be enhanced by the addition of
composites and dopants [16].
Composite engineering has emerged as a compelling approach to maximizing the thermoelectric
performance of materials. Thomas et al integrated SnSe composites into Cu
2
SnSe
3
samples and evaluated their
thermoelectric performance across a 10375 K temperature range. The ndings revealed that increasing the
SnSe content decreased carrier concentration, improving electrical resistivity and the Seebeck coefcient.
Particularly, the sample with x=10% demonstrated a noteworthy power factor of 35 μW/mΚ
2
at 375 K.
Additionally, the Seebeck coefcient of the 10% SnSe sample was approximately 3.6 times higher than that of the
pure material [2]. Zhao et al introduced graphene into Cu
2
SnSe
3
, and their study revealed that increasing the
proportion of graphene in the graphene/Cu
2
SnSe
3
samples resulted in a signicant increase in electrical
conductivity, accompanied by a decrease in the Seebeck coefcient. The integration of graphene nanosheets
effectively reduced thermal conductivity through enhanced phonon scattering at the graphene interface.
However, surpassing a certain threshold led to an elevation in the thermal conductivity of graphene/Cu
2
SnSe
3
composites. Remarkably, the highest achieved ZT for the 0.25 vol % graphene/Cu
2
SnSe
3
composite reached
0.44 at 700 K [17]. Nano-TiO
2
particles were incorporated into the Cu
2
SnSe
3
matrix via ball milling. The 1.4%
TiO
2
/Cu
2
SnSe
3
composite demonstrated enhanced electrical conductivity, but a reduced Seebeck coefcient
compared to pure Cu
2
SnSe
3
. While the Seebeck coefcient of various TiO
2
/Cu
2
SnSe
3
samples improved, their
electrical and thermal conductivities decreased due to reduced carrier conductivity. At 700 K,. achieved a ZT of
0.30 for the 1.0% TiO
2
/Cu
2
SnSe
3
composite [18].
The studies have demonstrated that composite engineering has improved the thermoelectric performance of
Cu
2
SnSe
3
-based materials. In this study, we introduced nickel (Ni)into the Cu
2
SnSe
3
matrix to examine the
impact of varying Ni concentrations on the thermoelectric properties of the resulting composites. We
systematically explored the electrical transport characteristics of Cu
2
SnSe
3
/x% Ni (where x=0, 1, 2, and 3 wt%)
composites across a temperature range spanning from 300 to 570 K. The expectation from the addition of Ni
into the composite is to potentially enhance specic thermoelectric properties such as electrical conductivity,
Seebeck coefcient, and ultimately the Power Factor. Nickels incorporation might introduce additional
scattering mechanisms for phonons and charge carriers, leading to optimized electrical and thermal transport
properties. By carefully tuning the Ni concentration, we aim to achieve an optimal balance between these
properties, thereby investigating the thermoelectric performance of the Cu
2
SnSe
3
-based composite materials.
2. Experimental details
2.1. Synthesis of Cu
2
SnSe
3
/x% Ni composites
Cu
2
SnSe
3
/x% Ni (where x=0, 1, 2, and 3 wt%)were made using the standard solid-state reaction technique.
Stochiometric ratios of extremely pure powders of copper (Cu, 99.7%, Loba Chemie), tin (Sn, 99.99%, Thermo
Scientic), and selenium (Se, 99.5%, Alfa Aeser)were weighed. The powders were mixed thoroughly using an
agate mortar and pestle for two and half hours and subjected to a hydraulic press that applied ve tons of
pressure to create rectangular pellets (dimensions: 11 ×6×1.5 mm
3
). Subsequently, the pellets were
pressurized to a high vacuum of 10
5
mbar while being sealed inside a quartz tube and then sintered at 500 °C
for 72 h using a mufe furnace. Then the pure nickel powder (99.9%, Alfa Aeser)was weighed following
stoichiometric ratios ranging from 1 to 3 wt% and added to prepared Cu
2
SnSe
3
samples. The mixture was then
reground for two hours to ensure the formation of homogeneous composites. The pellets were then sintered for
24 h at 400 °C in a pressure vacuum of 10
5
mbar. Cu
2
SnSe
3
with nickel composites were extremely dense and
uniform.
2.2. Characterizations
X-ray diffraction was performed with Cu-K
α
radiation (λ=1.5406 Å)to verify the materials phase formation
using the Rigaku Miniex 600 XRD system. A scanning rate of 1°/min was employed to the 2θrange 10°to 90°,
with a step size of 0.02°. Scanning Electron Microscopy (SEM)and Energy Dispersive Spectroscopy were used to
examine the surface morphology and elemental composition of the sample. SEM EVO MA-18 and Oxford
EDAX systems were utilized for the SEM-EDS measurements High-temperature electrical resistivity and
Seebeck coefcient measurements were conducted using the Linseis LSR-3 system. Hall measurements were
carried out by using the Ecopia HMS-5500 system using Van der Pauw technique to evaluate the carrier
concentration and Hall mobility.
2
Mater. Res. Express 11 (2024)076302 R Jagan et al
3. Results and discussion
3.1. XRD analysis
The x-ray diffraction (XRD)analysis was utilized to determine the crystal structure of Cu
2
SnSe
3
both with and
without the inclusion of Ni. Figure 1illustrates the XRD patterns of Cu
2
SnSe
3
/x% Ni samples and matches well
with JCPDS card no. 04-002-6015 [19], indicating that the structure is cubic with space group F
¯
4
3m which is in
line with previous reports [20,21]. Distinct peaks of high intensity are evident at approximately 2θvalues of
26.6°, 44.7°, 53.1°, 65.2°, and 72.1°[22,23]. In addition to the predominant presence of Cu
2
SnSe
3
,
supplementary phases arising from SnSe and the monoclinic phase of Cu
2
SnSe
3
are also evident. The type and
proportion of these secondary phases vary according to the x% value. Samples with 0% Ni display nearly
negligible secondary phases, indicating a predominance of pure Cu
2
SnSe
3
. Conversely, samples containing 1
and 2 wt% Ni exhibit minor occurrences of monoclinic Cu
2
SnSe
3
and traces of the SnSe phase. Notably, the
sample containing 3% Ni reveals the presence of both SnSe and monoclinic Cu
2
SnSe
3
, with overlap between Ni
and SnSe peaks alongside the major peaks [2,24,25].
Quantitative structural renement of x-ray diffraction (XRD)patterns of the composites was carried out
using Rietveld analysis with the help of FULLPROF software. The analysis focused on Cu
2
SnSe
3
cubic phases
with the (F
¯
4
3m)space group for the renements. A comparison of the simulated and experimental data for
each sample is shown in gure 2. The rened structural parameters and the goodness-of-t indicators like R
p
,
R
wp
,R
exp
, and χ
2
are listed in table 1[2]. There is a small decrease in the lattice parameter for x=1% and 2% Ni
as compared to x=0% Ni which could be due to the off stoichiometry [26], and for x=3% Ni sample lattice
parameter is slightly increased might be due to the Ni atoms occupying the interstitial sites of Cu
2
SnSe
3
[2]. The
lattice parameters found in the literature for Cu
2
SnSe
3
are in good agreement [27,28].
To obtain the precise crystallite size Scherrer, W-H, and Size-Strain methods, were employed.
()
l
bq
=Dk
Cos 2
()bqleq=+
k
D
Cos 4 sin 3
⎜⎟
() () ()/bql bq
le=+dk
D
d
cos cos 24
222
where
q
is the Bragg angle,
k
=0.9 is the shape factor, bis the corrected full width at half maximum
(FWHM)in radian,
l
is the x-ray wavelength in nm,
e
is the strain,
d
is the interplanar spacing in nm and
D
is
the crystallite size in nm [29,30]. The crystallite size obtained is tabulated in table 2. Crystallite sizes ranging
from 22 to 26 nm, 56 to 93 nm, and 69 to 140 nm were determined using the Scherrer, Size-Strain Plot (SSP), and
Figure 1. X-ray diffraction prole of Cu
2
SnSe
3
/x% Ni (where x =0, 1, 2, and 3 wt%)where ()shows the presence of SnSe phase, ()
shows the presence of monoclinic Cu
2
SnSe
3
phase and (#)shows the presence of Ni peak.
3
Mater. Res. Express 11 (2024)076302 R Jagan et al
WilliamsonHall (W-H)methods, respectively. The results obtained from the SSP method and W-H method
are illustrated in gure 3. A large difference in the crystallite size is observed between Scherrer and W-H method.
It is attributed to the introduction of defects or dislocations in the crystal structure with the addition of Ni. These
defects can affect the peak broadening in XRD patterns, inuencing the WH method results more than the
Scherrer method, which assumes ideal crystal conditions without considering defects. Considering the delity of
the ts achieved, we conclude that the crystallite size and micro-strain derived through the SSP method exhibit
superior reliability compared to the other two methodologies applied to the samples under current
investigation.
Figure 2. Rietveld rened analysis of Cu
2
SnSe
3
/x% Ni (x=0, 1, 2, and 3 wt%).
Table 1. Rietveld rened parameters of Cu
2
SnSe
3
/x% Ni (x=0, 1, 2, and
3 wt%).
Cu
2
SnSe
3
/x%Ni x=0% x=1% x=2% x=3%
System Cubic Cubic Cubic Cubic
Space group
¯
43m ¯
43m ¯
43m ¯
F
43m
a=b=c(Å)5.695
(0.0001)
5.694
(0.0001)
5.693
(0.0001)
5.695
(0.0001)
α=β=γ(°)90 90 90 90
Cell volume (Å
3
)184.70
(0.04)
184.56
(0.04)
184.53
(0.04)
184.69
(0.05)
R
p
5.35 5.14 5.61 5.97
R
wp
6.93 6.70 7.48 8.60
R
exp
4.60 4.69 4.79 4.51
χ
2
2.27 2.04 2.43 3.63
4
Mater. Res. Express 11 (2024)076302 R Jagan et al
3.2. SEM-EDS analysis
The surface morphology of Cu
2
SnSe
3
/x% Ni (where x=0, 1, 2, and 3 wt%)are shown in gure 4. The sample
surface is homogenous and uniform. With the increasing concentration of Ni, there is a decrease in the porosity.
Incorporating Nickel into the Cu
2
SnSe
3
matrix establishes a conductive framework favourable to the transport
of charge carriers within these materials. The acquired data aligns with the results obtained from Hall
measurements (table 4), conrming the effectiveness of this addition in facilitating charge carrier transport. The
presence of Cu, Sn, Se, and Ni is conrmed with EDS analysis, given in gure 5. The x-ray elemental mapping
reveals a consistent and homogeneous distribution of the constituent elements (Cu, Sn, Se, and Ni)across
specic areas of the samples, conrming their chemical and structural uniformity, as depicted in the gure 6[31]
and the prepared samples chemical composition is shown in table 3.
3.3. Electrical transport studies
3.3.1. Electrical resistivity
The electrical resistivity of Cu
2
SnSe
3
samples with x=0, 1, 2, and 3 wt% Ni composites was measured across the
temperature range of 300570 K and depicted in gure 7(a). The resistivity of the pristine sample at room
temperature was found to be 3 ×10
3
μΩ-m which is in accordance with the already existing data [26]. As the
temperature increased, the resistivity of each sample gradually decreased, indicating a non-degenerate
semiconductor behaviour consistent with earlier reports [28,32]. The introduction of Ni into Cu
2
SnSe
3
samples
has a notable impact on their resistivity. Specically, the sample containing 3% Ni exhibits an approximately
eight-fold decrease in electrical resistivity compared to the pure sample at room temperature (See gure 7(b)).
This reduction in resistivity suggests the effective activation of Ni atoms as electron donors within the material.
The observed decrease in resistivity with Ni composites can be attributed to the additional electrons or free
charge carriers contributed by Ni to the Fermi level [33]. Also, this linear decline in electrical resistivity with
increasing nickel content corresponds to the concurrent rise in carrier concentration,
n
and the decrease in
mobility (μ), as indicated in table 4[34,35].
3.3.2. Seebeck coefcient
The Seebeck coefcient, Sof Cu
2
SnSe
3
/x% Ni (where x=0, 1, 2, and 3 wt%)between the temperature range
300570 K is shown in gure 8(a). The results showed that most charge carriers are holes indicating the sample
synthesized is a p-type semiconductor. It is reected in the Hall measurements where we have obtained a positive
Figure 3. (a)Size-strain and(b)WH plot of Cu
2
SnSe
3
/x% Ni (x=0, 1, 2, and 3 wt%).
Table 2. Crystallite size estimated using different methods.
Nickel concentration (x%)Scherrer method W-H method Size -strain method
Crystallite size (nm)Crystallite size (nm)Strain (10
3
)Crystallite size (nm)Strain (10
3
)
0% 25 ±185±8 2.05 80 ±5 2.08
1% 22 ±169±7 2.42 56 ±5 2.21
2% 26 ±1 140 ±14 2.33 93 ±14 2.16
3% 26 ±2 101 ±10 2.13 79 ±10 2.01
5
Mater. Res. Express 11 (2024)076302 R Jagan et al
value of carrier concentration for all the synthesized samples as shown in table 4[2]. At room temperature, the S
value of 378 μV/K is obtained, in line with the earlier reports [36,37]. The addition of Ni has signicantly
reduced the Seebeck coefcient as shown in gure 8(b)attributed to the increase in charge carrier density
()
n
as
described in Motts law.
Motts elucidation of the diffusion thermoelectric power within the framework of the degenerate free-
electron approximation, as given in equation (5)[30,38].
(()) ()
pse
e
=-
seknE
3
ln 5
BF
22
where
()
s
e
denotes the electrical conductivity at the Fermi level, erepresents the elementary charge,
kB
is the
Boltzmann constant, and
E
F
indicating the Fermi energy. Within pure metallic systems, particularly within the
Figure 4. SEM images of Cu
2
SnSe
3
/x% Ni (x=0, 1, 2, and 3 wt%).
Figure 5. Representative EDS spectra of (a)Cu
2
SnSe
3
/0% Ni and (b)Cu
2
SnSe
3
/1% Ni.
6
Mater. Res. Express 11 (2024)076302 R Jagan et al
Figure 6. EDS mapping of the Cu
2
SnSe
3
/x% Ni (where x =0 and 1 wt%).
Figure 7. (a)Temperature-dependent electrical resistivity data of Cu
2
SnSe
3
/x% Ni (where x =0, 1, 2, and 3 wt%)and (b)Resistivity as
a function of x % Ni concentration.
Table 3. EDS results of Cu
2
SnSe
3
/x% Ni (where x =0, 1, 2, and 3 wt%).
Samples Cu (Atomic %)Sn (Atomic %)Se (Atomic %)Ni (Atomic %)
x=0% 35.22 18.12 46.66 0
x=1% 36.87 15.76 45.04 2.33
x=2% 38.85 15.07 41.90 4.19
x=3% 38.85 14.68 40.80 5.66
Table 4. Bulk concentration, Hall mobility, weighted mobility, and effective mass at room temperature of Cu
2
SnSe
3
/x% Ni
(where x =0, 1, 2, and 3 wt%)samples.
Sample Bulk concentration (
)
´-
cm1018 3 Mobility
(
)
--
cm V s
211 Weighted mobility,
m
w(cm
2
/V-s)m
*
/m
e
x=0% 1.50 18.8 11.90 0.24
x=1% 4.99 14.5 4.30 0.27
x=2% 18.8 6.17 1.64 0.36
x=3% 84.3 3.83 1.72 0.47
7
Mater. Res. Express 11 (2024)076302 R Jagan et al
temperature range where electronphonon scattering prevails [39], the expression for the diffusion thermo-
electric power (TEP)can be formulated as follows:
()
p
=-SkT
eE 6
B
F
22
()
*
pp
=Sk
eh mnT
8
33 7
dB
22
2
2
3
The reduction in the Seebeck coefcient with increasing temperature and Ni concentration can be explained
using Motts equation and this trend is in line with the resistivity data displayed in gure 7. This equation enables
the estimation of the effective mass of the electron
(
)
*
mwithin the degenerate regime [4,40]which is shown in
table 4. The highest observed value of the Seebeck coefcient is 482 μV/K for the pristine sample, decreasing to
85 μV/K and 68 μV/K for samples with x=1 and 2 wt% of Ni at 570 K respectively.
In materials characterized by low mobility, it is commonly acknowledged that the weighted mobility
(
)m
,
w
dened as electron mobility weighted by the density of electronic states, provides a more accurate estimate of
drift mobility compared to Hall mobility. Consequently, in such materials, relying solely on Hall measurements
for estimating carrier mobility (μ)may yield erroneous results. Therefore, our investigation has involved
estimating the weighted mobility of carriers for all compounds under study, to gain insight into their transport
properties [26,41]. Equation (8)delineates the weighted mobility, a parameter proposed by Snyder et al which
remains unaffected by carrier density variations. According to their proposition, the expression for weighted
mobility is as follows [42]:
⎜⎟ ⎜⎟
()
∣∣
∣∣
∣∣
∣∣
()
/
/
/
/
ms
p
p
=
-
+- -
+
+-
h
emkT
exp s
ke
exp s
ke
s
ke
exp s
ke
3
82
2
151
3
15 1
8
w
eB
B
B
B
B
3
32
2
In this context,
s
denotes the electrical conductivity at a specic temperature
T.
The values of
m
w
for each
sample examined at room temperature is provided in table 4.
3.3.3. Lorenz number
Evaluating the Lorenz number stands as a crucial aspect in the exploration of degeneracy of materials. Lorenz
number is dened by the WiedemannFranz law as the ratio of electronic thermal conductivity
(
)keto the
product of absolute temperature (T)and electrical conductivity
(
)swhich is given by the equation [43],
()
k
s
=LT9
e
According to Kim et al this parameter can be effectively linked to the absolute value of the Seebeck coefcient
throughout the entirety of the temperature spectrum by the equation [44],
Figure 8. (a)Temperature-dependent Seebeck coefcient of Cu
2
SnSe
3
/x% Ni (where x =0, 1, 2, and 3 wt%)and (b)Seebeck
coefcient as a function of x % Ni concentration.
8
Mater. Res. Express 11 (2024)076302 R Jagan et al
∣∣ ∣∣ ()=- -+ -LSS
1.49 0.49 exp 21 1.49 exp 85 10
kim
Where unit of
L
ki
m
is in 10
8
WΩK
2
and Sis in μV/K. This approximation aligns closely with the single
parabolic band model with the assumption of acoustic phonon scattering with an error of 0.5%. Various
scattering mechanisms and temperature can modify the degenerate value 2.44 ×10
8
WΩK
2
in highly
degenerate semiconductor materials. The current investigation involves assessing the temperature-dependent
Lorenz number within the range of 300570 K, as described by equation (10)and depicted in gure 9. At room
temperature
L
ki
m
value is observed to be 1.51 ×10
8
WΩK
2
for pristine sample, and it is found to be constant
throughout the measured temperature range. It is due to the negligible variation in Seebeck coefcient with
temperature. The addition of Ni has further increased the Lorenz number, heading towards the degenerate
behaviour as reected in the reduced resistivity values (See gure 7). The obtained values of
L
ki
m
are fall within
the degenerate limit [45].
3.3.4. Power factor
The temperature-dependent power factor (PF)of Cu
2
SnSe
3
/x% Ni (where x=0, 1, 2, and 3 wt%)is examined
within the temperature range of 300570 K is shown in gure 10(a). It is derived from the Seebeck coefcient
and electrical resistivity
r
=PF S.
2
The obtained results demonstrate an increasing trend with temperature for
Figure 9. Plot of Lorenz number with the temperature of Cu
2
SnSe
3
/x% Ni (where x =0, 1, 2, and 3 wt%).
Figure 10. (a)Temperature-dependent Power factor of Cu
2
SnSe
3
/x% Ni (where x =0, 1, 2, and 3 wt%)and (b)Power Factor as a
function of x % Ni concentration.
9
Mater. Res. Express 11 (2024)076302 R Jagan et al
the pristine sample. However, with the increment in Ni content, there is a notable decline in the
P
F
value across
the system. This variation in
P
F
among the synthesized samples is graphically depicted in gure 10(b). Notably,
the pristine sample achieves the highest
P
F
value of 420 μW/mK
2
at 570 K consistent with prior reports
[26,28]. The decrease of PF value with Ni addition mainly arises from the signicant reduction in the Seebeck
coefcient. The comparison results with the available literature are tabulated in table 5. It indicates that material
in the present work is moderately efcient for the thermoelectric application.
4. Conclusion
In conclusion, our investigation comprehensively examined the thermoelectric characteristics of Cu
2
SnSe
3
/x%
Ni (where x=0, 1, 2, and 3 wt%)systems over a temperature range spanning 300570 K. X-ray diffraction
(XRD)analysis veried the polycrystalline nature of all synthesized samples, revealing a consistent cubic
structure with the ¯
F
43m space group. The observed decrease in resistivity and Seebeck coefcient of the
composites compared to the pristine material can be attributed to the increased carrier concentration resulting
from Ni introduction. Remarkably, the sample containing 3% Ni exhibited an approximate eight-fold reduction
in electrical resistivity compared to the pure sample at room temperature, indicating enhanced charge transport
efciency. Despite achieving the highest power factor
()
PF
value of approximately 420 μW/mK
2
at 570 K, an
overall decreasing trend in the PF value is seen with the addition of Ni, due to the adverse effect of the Seebeck
coefcient. Hence our investigations highlight the predominant reduction in the electrical resistivity with the
addition of Ni.
Acknowledgments
One of the authors (RJ)acknowledges the Manipal Academy of Higher Education for providing nancial
support and the author (AR)acknowledges the DST - FIST grant (SR/FIST/PS-1/2017/8)and Council of
Scientic, and Industrial Research Grant (Sanction no: 03(1409)/17/EMR-II)for the nancial support required
for this work.
Data availability statement
The data cannot be made publicly available upon publication because they are not available in a format that is
sufciently accessible or reusable by other researchers. The data that support the ndings of this study are
available upon reasonable request from the authors.
ORCID iDs
Poornesh P https://orcid.org/0000-0002-3608-6294
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