The development of new sulfide and selenide-based thermoelectric (TE) materials is critical for the mass production of TE devices due to the higher earth abundance of S/Se than Te. In this work, we ...have prepared single crystals of Ag-substituted BaCu2−xAgxSe2 (x = 0 – 0.8) by direct fusion of elements at high temperatures. As characterized by single crystal X-ray diffraction (SCXRD) studies, each of the structures (space group: Pnma) contains two transition metal sites (M1 and M2), and the Ag atoms are disordered with Cu atoms at both sites with a slight preference for the M2 site. Phase pure polycrystalline BaCu2−xAgxSe2 (x = 0 – 1.0) samples have also been synthesized, which are semiconductors as confirmed by optical absorption and resistivity studies. All these samples show positive values of the Seebeck coefficient, suggesting the p-type electrical conduction. Our thermal conductivity (ktot) studies demonstrate a remarkable drop in ktot values on increasing the Ag-substitution in the BaCu2−xAgxSe2 phases with the lowest ktot value of 0.33 W m−1 K−1 (673 K) for the x = 1.0 sample. Our studies show the potential of the BaCuAgSe2 for TE applications with higher zT values if the hole concentration of the phase can be fully optimized.
The design of new complex mixed metal tellurides (containing low toxicity cations) with intrinsic ultralow thermal conductivity is of paramount importance in the field of thermoelectrics. Herein, we ...report the synthesis and characterization of polycrystalline and single crystals of a new mixed-metal quaternary telluride Mn1.8(1)In0.8(1)Si2Te6. The structural aspects and chemical formula of this phase at room temperature have been established using single crystal X-ray diffraction and EDX studies. The trigonal centrosymmetric (space group: P31m) structure of the title phase has cell constants of a = b = 7.0483(7) Å and c = 7.1277(8) Å. The structure has three independent cationic sites, one mixed (In1/Mn1), one partially filled Mn2, and one Si1, which are bonded with Te1 atoms. Each metal atom (In and Mn) in the structure is octahedrally coordinated with six neighboring Te1 atoms. The structure also features dimers of Si atoms, and each Si atom is bonded to three Te1 atoms to form ethane-like Si2Te6 units. The optical absorption study of a polycrystalline Mn1.8In0.8Si2Te6 sample shows a narrow optical bandgap of 0.6(2) eV. Temperature-dependent resistivity and Seebeck coefficient studies confirmed the p-type semiconducting nature of the sample with high values of S (301 μV K−1 to 444 μV K−1). The total thermal conductivity (ktot) study of the polycrystalline sample shows a decreasing trend on heating with an extremely low value of 0.28 W m−1 K−1 at 773 K. Magnetic measurements indicate a glassy magnetic behavior for the sample below 8 K.
We report the synthesis of single crystals of the quaternary sulfide, BaCeCuS3, for the first time by heating a polycrystalline sample of BaCeCuS3 with an excess of KCl flux inside a vacuum-sealed ...fused silica tube. The crystal structure of the compound is determined by a single-crystal X-ray diffraction study which shows that it crystallizes in the primitive orthorhombic crystal system (space group: Pnma) with cell constants of a = 10.6740(13) Å, b = 4.1200(6) Å, and c = 13.409(2) Å. The structure is best described as a pseudo-two-dimensional structure where tetrahedral CuS4 and octahedral CeS6 units serve as the main building blocks. The polyanionic Formula Omitted layers in the structure are separated by the presence of electropositive Ba2+ cations. The optical absorption study on the polycrystalline sample of BaCeCuS3 shows a semiconducting nature with a direct bandgap of 1.8(2) eV consistent with the green color of the sample. The temperature-dependent thermal conductivity (ktot) measurements on the polycrystalline BaCeCuS3 sample reveal an extremely low value of ktot (0.32 W m−1 K−1) at 773 K. DFT calculations were carried out to obtain the electronic structure of the title compound. Our theoretical studies predict a high value of the thermoelectric figure of merit (>1) for BaCeCuS3 by optimization of the charge carriers. To also explore a practical application of BaCeCuS3, a liquid junction solar cell was fabricated: TiO2/CdS/BaCeCuS3/Sn2−/S2−/MWCNTs@Ni, and the cell delivered an efficiency enhanced by ∼45% compared to the one without the sulfide. The performance improvement is affected by the hole conducting properties of BaCeCuS3, which allows facile hole transfer from CdS to the polysulfide, increases the charge separation, and hence increases the efficiency.
The development of new sulfide and selenide-based thermoelectric (TE) materials is critical for the mass production of TE devices due to the higher earth abundance of S/Se than Te. In this work, we ...have prepared single crystals of Ag-substituted BaCu
2−
x
Ag
x
Se
2
(
x
= 0 - 0.8) by direct fusion of elements at high temperatures. As characterized by single crystal X-ray diffraction (SCXRD) studies, each of the structures (space group:
Pnma
) contains two transition metal sites (M1 and M2), and the Ag atoms are disordered with Cu atoms at both sites with a slight preference for the M2 site. Phase pure polycrystalline BaCu
2−
x
Ag
x
Se
2
(
x
= 0 - 1.0) samples have also been synthesized, which are semiconductors as confirmed by optical absorption and resistivity studies. All these samples show positive values of the Seebeck coefficient, suggesting the p-type electrical conduction. Our thermal conductivity (
k
tot
) studies demonstrate a remarkable drop in
k
tot
values on increasing the Ag-substitution in the BaCu
2−
x
Ag
x
Se
2
phases with the lowest
k
tot
value of 0.33 W m
−1
K
−1
(673 K) for the
x
= 1.0 sample. Our studies show the potential of the BaCuAgSe
2
for TE applications with higher
z
T values if the hole concentration of the phase can be fully optimized.
Single crystals and phase pure polycrystalline BaCu
2−
x
Ag
x
Se
2
samples have been synthesized to study the effect of Ag substitution on their structural parameters and physical properties.
The development of new sulfide and selenide-based thermoelectric (TE) materials is critical for the mass production of TE devices due to the higher earth abundance of S/Se than Te. In this work, we ...have prepared single crystals of Ag-substituted BaCu 2− x Ag x Se 2 ( x = 0 – 0.8) by direct fusion of elements at high temperatures. As characterized by single crystal X-ray diffraction (SCXRD) studies, each of the structures (space group: Pnma ) contains two transition metal sites (M1 and M2), and the Ag atoms are disordered with Cu atoms at both sites with a slight preference for the M2 site. Phase pure polycrystalline BaCu 2− x Ag x Se 2 ( x = 0 – 1.0) samples have also been synthesized, which are semiconductors as confirmed by optical absorption and resistivity studies. All these samples show positive values of the Seebeck coefficient, suggesting the p-type electrical conduction. Our thermal conductivity ( k tot ) studies demonstrate a remarkable drop in k tot values on increasing the Ag-substitution in the BaCu 2− x Ag x Se 2 phases with the lowest k tot value of 0.33 W m −1 K −1 (673 K) for the x = 1.0 sample. Our studies show the potential of the BaCuAgSe 2 for TE applications with higher z T values if the hole concentration of the phase can be fully optimized.
We report the synthesis of crystals of a new ternary polyselenide Ba8Zr2Se11(Se2). The title compound has a pseudo-zero-dimensional crystal structure (space group: C2/c) with a unique structure type ...as determined by a single-crystal X-ray diffraction study. Each Zr atom of the structure is connected to six Se atoms, forming a distorted octahedral coordination geometry. The ZrSe6 octahedron is fused with the one neighboring octahedral unit via the sharing of one corner to form isolated dimeric Zr2Se1114− units. Some of the Se atoms of the structure form Se22− dimers and are only coordinated to the Ba atoms. A polycrystalline Ba8Zr2Se11(Se2) sample is found to be a semiconductor (Eg = 1.9(2) eV). A small total thermal conductivity of 0.59 Wm−1K−1 (at 773 K) was observed for the sample. The solar cell study on the Ba8Zr2Se11(Se2) powder showed an efficiency enhancement of 9.8% with its inclusion in the cell based on TiO2/CdS as the photoanode, due to a suppressed electron-hole recombination rate. DFT calculations are also carried out to study the electronic structure of the compound.
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•The ternary polychalcogenide Ba8Zr2Se11(Se2) was successfully synthesized and characterized.•It is the first polychalcogenide in the Ba–Zr-Q system with unique structure type having pseudo-zero-dimensional structure.•The photovoltaic study of Ba8Zr2Se11(Se2) showed an enhaced efficiency of 9.8%.•The Ba8Zr2Se11(Se2) showed a low thermal conductivity.value of 0.59 Wm−1K−1 at 773 K.
The design of new complex mixed metal tellurides (containing low toxicity cations) with intrinsic ultralow thermal conductivity is of paramount importance in the field of thermoelectrics. Herein, we ...report the synthesis and characterization of polycrystalline and single crystals of a new mixed-metal quaternary telluride Mn
In
Si
Te
. The structural aspects and chemical formula of this phase at room temperature have been established using single crystal X-ray diffraction and EDX studies. The trigonal centrosymmetric (space group:
3̄1
) structure of the title phase has cell constants of
=
= 7.0483(7) Å and
= 7.1277(8) Å. The structure has three independent cationic sites, one mixed (In1/Mn1), one partially filled Mn2, and one Si1, which are bonded with Te1 atoms. Each metal atom (In and Mn) in the structure is octahedrally coordinated with six neighboring Te1 atoms. The structure also features dimers of Si atoms, and each Si atom is bonded to three Te1 atoms to form ethane-like Si
Te
units. The optical absorption study of a polycrystalline Mn
In
Si
Te
sample shows a narrow optical bandgap of 0.6(2) eV. Temperature-dependent resistivity and Seebeck coefficient studies confirmed the
-type semiconducting nature of the sample with high values of
(301 μV K
to 444 μV K
). The total thermal conductivity (
) study of the polycrystalline sample shows a decreasing trend on heating with an extremely low value of 0.28 W m
K
at 773 K. Magnetic measurements indicate a glassy magnetic behavior for the sample below 8 K.
The design of new complex mixed metal tellurides (containing low toxicity cations) with intrinsic ultralow thermal conductivity is of paramount importance in the field of thermoelectrics. Herein, we ...report the synthesis and characterization of polycrystalline and single crystals of a new mixed-metal quaternary telluride Mn
1.8(1)
In
0.8(1)
Si
2
Te
6
. The structural aspects and chemical formula of this phase at room temperature have been established using single crystal X-ray diffraction and EDX studies. The trigonal centrosymmetric (space group:
P
3&cmb.macr;1
m
) structure of the title phase has cell constants of
a
=
b
= 7.0483(7) Å and
c
= 7.1277(8) Å. The structure has three independent cationic sites, one mixed (In1/Mn1), one partially filled Mn2, and one Si1, which are bonded with Te1 atoms. Each metal atom (In and Mn) in the structure is octahedrally coordinated with six neighboring Te1 atoms. The structure also features dimers of Si atoms, and each Si atom is bonded to three Te1 atoms to form ethane-like Si
2
Te
6
units. The optical absorption study of a polycrystalline Mn
1.8
In
0.8
Si
2
Te
6
sample shows a narrow optical bandgap of 0.6(2) eV. Temperature-dependent resistivity and Seebeck coefficient studies confirmed the
p
-type semiconducting nature of the sample with high values of
S
(301 μV K
−1
to 444 μV K
−1
). The total thermal conductivity (
k
tot
) study of the polycrystalline sample shows a decreasing trend on heating with an extremely low value of 0.28 W m
−1
K
−1
at 773 K. Magnetic measurements indicate a glassy magnetic behavior for the sample below 8 K.
The first quaternary telluride, Mn
1.8(1)
In
0.8(1)
Si
2
Te
6
, of the Mn-In-Si-Te system has been synthesized and characterized. The phase shows ultralow thermal conductivity (0.28 W m
−1
K
−1
at 773 K) values.
•Three quaternary chalcogenides, BaCeCuSe3, BaCeAgS3, and BaCeAgSe3, were synthesized and characterized.•The BaCeCuSe3 exhibited ultralow thermal conductivity (0.43 Wm−1K−1) at 773 K.•The optical ...absorption bandgap studies showed the semiconducting nature of the three compounds.•The photovoltaic study of BaCeAgS3 showed the highest efficiency of ∼4% among the three compounds.•Theoretical thermoelectric studies show a zT value of >1 on hole-doping in the BaCeCuSe3.
In this study, we present the syntheses of three chalcogenides, BaCeCuSe3, BaCeAgS3, and BaCeAgSe3, using the sealed-tube method. The single-crystal X-ray diffraction technique is employed to determine the structures of BaCeAgQ3 (Q = S/Se) for the first time. These isostructural Ag-containing compounds (space group: Cmcm) crystallize in the KCuZrS3 structure type. Rietveld refinement study of the BaCeCuSe3 sample confirms its orthorhombic Eu2CuS3 type structure (Pnma). The building blocks of these pseudo-two-dimensional structures are tetrahedral MQ4 (M = Cu/Ag) and octahedral CeQ6 polyhedra, which are conjoined to form ∞2CeMQ32− layer. The optical absorption studies reveal the semiconducting nature of the BaCeMQ3 with bandgaps of 1.4(2) eV-1.5(2) eV consistent with their electronic structures calculated using DFT studies. The thermal conductivity (ktot) measurements showed extremely low ktot values (0.43–0.67 Wm−1K−1) for these samples at 773 K. Solar cells were fabricated with the chalcogenides and the highest efficiency of ∼4% was achieved with BaCeAgS3.
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In this report, we have investigated the structure and properties of the 12-BaBi2S4. A single crystal X-ray diffraction study shows that the 12-BaBi2S4 crystallizes in the hexagonal crystal system ...(space group = P63/m) with refined lattice parameters of a = b = 25.2687(10) Å, c = 4.1859(2) Å, and formula unit = Z = 12 at room temperature. The structure contains fifteen crystallographic independent sites, including three Ba, four Bi, and eight types of S atoms. A phase pure polycrystalline sample of 12-BaBi2S4 was synthesized by heating stoichiometric amounts of BaCO3 and Bi2O3 under a CS2 atmosphere. The phase pure sample is found to be a semiconductor with a direct bandgap of 1.3(1) eV. The polycrystalline 12-BaBi2S4 exhibits ultra-low thermal conductivity values, varying from 0.47 Wm−1K−1 at 323 K to 0.43 Wm−1K−1 at 773 K. The sample shows high values of the Seebeck coefficient (S = −300 μV/K to −210 μV/K) in the 323 K–773 K range with poor electrical conductivity values. The negative sign of the S implies that the sample is a n-type semiconductor. DFT studies of the 12-BaBi2S4 also predict semiconducting properties. We have explored the 12-BaBi2S4 sample for photovoltaic (PV) applications by fabricating a liquid junction solar cell, TiO2/CdS/12-BaBi2S4/Sn2−/S2−/MWCNTs@Ni, which delivered an efficiency enhanced by ∼12 % to the control cell based on sole CdS as the photo-sensitizer. Theoretical electronic structure calculations suggest the semiconducting nature of the 12-BaBi2S4 in agreement with the optical absorption and electrical resistivity studies.
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•12 BaBi2S4 exhibits ultralow thermal conductivity values ranging from 0.47 W/mK (323 K) to 0.43 W/mK (773 K).•The optical absorption study of 12 BaBi2S4 reveals the semiconducting behavior of the sample.•The Seebeck coefficient measurements confirm the n-type semiconducting nature of the sample.•The photovoltaic study showed a 12 % increment in the efficiency.
