Crystalline Structure-Dependent Mechanical and Thermoelectric Performance in <span class="mag-xml-inline-formula"><math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>A</mml:mtext><mml:msub><mml:mrow><mml:mtext>g</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mtext>S</mml:mtext><mml:msub><mml:mrow><mml:mtext>e</mml:mtext></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mo>‐</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mrow><mml:mtext>S</mml:mtext></mml:mrow><mml:mrow><mml:mi>x</mml:mi></mml:mrow></mml:msub></math></span> System

Crystalline Structure-Dependent Mechanical and Thermoelectric Performance in $A g 2 S e 1 ‐ x S x$ System

PDF

Jiasheng Liang¹^,², Pengfei Qiu¹, Yuan Zhu³, Hui Huang¹^,², Zhiqiang Gao¹^,²^,⁴, Zhen Zhang³, Xun Shi¹, Lidong Chen¹^,²

Research. Vol 2020 Article ID 6591981

Less

Research. Vol 2020 Article ID 6591981

• Research Article •

Crystalline Structure-Dependent Mechanical and Thermoelectric Performance in

A g 2 S e 1 ‐ x S x

System

Full

Jiasheng Liang¹^,², Pengfei Qiu¹, Yuan Zhu³, Hui Huang¹^,², Zhiqiang Gao¹^,²^,⁴, Zhen Zhang³, Xun Shi¹, Lidong Chen¹^,²

Affiliations

¹State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China

²Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China

³Division of Solid-State Electronics, Department of Electrical Engineering, Uppsala University, Uppsala, Sweden

⁴School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China

About Author:

Authors’ Contributions

P.Q., X.S., and L.C. conceived the idea. J.L. conducted the synthesis, TE transport property measurement, and bending test. Z.G. and H.H. conducted the Hall measurement and Vickers hardness measurements. J.L, P.Q., Y.Z. and Z.Z. contributed to data analysis, model interpretation, and paper drafting. J.L., P.Q., and X.S. completed the writing of the manuscript. All authors discussed the results and gave comments regarding the manuscript.

Published: 2020-07-20 doi: 10.34133/2020/6591981

Outline

Abstract

Less

Self-powered wearable electronics require thermoelectric materials simultaneously with a high dimensionless figure of merit ( $z T$ ) and good flexibility to convert the heat discharged by the human body into electricity. Ag₂(S,Se)-based semiconducting materials can well satisfy these requirements, and thus, they are attracting great attention in thermoelectric society recently. Ag₂(S,Se) crystalizes in an orthorhombic structure or monoclinic structure, depending on the detailed S/Se atomic ratio, but the relationship between its crystalline structure and mechanical/thermoelectric performance is still unclear to date. In this study, a series of $A g 2 S e 1 ‐ x S x$ ( $x = 0$ , 0.1, 0.2, 0.3, 0.4, and 0.45) samples were prepared and their mechanical and thermoelectric performance dependence on the crystalline structure was systematically investigated. $x = 0.3$ in the $A g 2 S e 1 ‐ x S x$ system was found to be the transition boundary between orthorhombic and monoclinic structures. Mechanical property measurement shows that the orthorhombic $A g 2 S e 1 ‐ x S x$ samples are brittle while the monoclinic Ag₂Se_1‐xS_x samples are ductile and flexible. In addition, the orthorhombic $A g 2 S e 1 ‐ x S x$ samples show better electrical transport performance and higher $z T$ than the monoclinic samples under a comparable carrier concentration, most likely due to their weaker electron-phonon interactions. This study sheds light on the further development of flexible inorganic TE materials.

Cite this Article

Jiasheng Liang, Pengfei Qiu, Yuan Zhu, Hui Huang, Zhiqiang Gao, Zhen Zhang, Xun Shi, Lidong Chen. Crystalline Structure-Dependent Mechanical and Thermoelectric Performance in

A g 2 S e 1 ‐ x S x

System[J]. Research, 2020 , 2020 (7) : 6591981 - . DOI: 10.34133/2020/6591981

Full Text

Less

1. 　Introduction

Less

Recently, thermoelectric (TE) technology shows a great potential to be used as a sustainable power source in wearable electronics [1–3]. Via harvesting the heat discharged by the human body and converting it into electricity, the wearable electronics using TE technology can be self-powered without using any external batteries. The energy conversion efficiency of a TE material is determined by the dimensionless figure of merit,

z T = α 2 σ T / κ

, where

α

is the Seebeck coefficient,

σ

is the electrical conductivity,

κ

is the thermal conductivity, and

T

is the absolute temperature. The TE material used in wearable electronics should possess high

z T

to maximize the energy conversion efficiency and good flexibility to match the curved surface of skin and endure repeated bending during service [4–6].

To date, Bi₂Te₃-based alloys are still the best room-temperature TE materials, but their application in wearable electronics is limited due to their inherent brittleness [7–14]. In contrast, the organic TE polymers show good flexibility, but their

z T

s are low [15–20]. Recently, we reported a class of Ag₂S-based flexible inorganic TE materials with excellent intrinsic flexibility and high

z T

s [21]. Monoclinic Ag₂S shows surprisingly high ductility at room temperature due to its wrinkled layer structure (space group

P 21 / n

, with the sketch map shown in Figure 1(a), and weak Ag-S chemical bonds [22, 23]. However, its relatively wide band gap (around 1 eV) yields low

σ

only in the order of 10^-1 S m^-1. As a result,

z T

of the stoichiometric Ag₂S around room temperature is very poor. Alloying Se or/and Te in Ag₂S can significantly improve

σ

and enhance

z T

to 0.26 for Ag₂S_0.5Se_0.5 and 0.44 for Ag₂S_0.5Se_0.45Te_0.05 at 300 K. Particularly, previous study showed that the good ductility can be well maintained when the Se alloying content in Ag₂S reaches 50% or the Te alloying content reaches 20%, enabling these materials very suitable to be used in flexible wearable electronics. The above results arouse great interest on the Ag₂S-based materials in TE society [21, 23–25].

Being different with ductile Ag₂S, Ag₂Se is a brittle material. It adopts an orthorhombic structure (space group

P 212121

) with the sketch map shown in Figure 1(b). The band gap of orthorhombic Ag₂Se is around 0.2 eV, about one-fifth of that of monoclinic Ag₂S. Orthorhombic Ag₂Se has very high carrier mobility (~10³ cm^-2 V^-1 S^-1), excellent

σ

(~10⁵ S m^-1), and extremely low lattice thermal conductivity (~0.3-0.5 W m^-1 K^-1), resulting in high

z T

about 0.4~1.0 at 300 K [26–32]. Despite the different crystalline structures of Ag₂S and Ag₂Se, Bindi and Pingitore [33] reported that Ag₂S and Ag₂Se can form a continuous solid solution. The room-temperature crystalline structure of

A g 2 S 1 ‐ x S e x

solid solution is the same with the monoclinic Ag₂S when

x ≤ 0.6

, but the same with the orthorhombic Ag₂Se when

x ≥ 0.7

. Considering that the carrier concentration of Ag₂Se is about several orders of magnitude higher than that of Ag₂S [22],

A g 2 S 1 ‐ x S e x

solid solution might process continuous adjustable carrier concentrations and TE properties. The mechanical properties and TE performance of

A g 2 S e 1 ‐ x S x

(

0.5 ≤ x ≤ 1

) have been already reported previously [33], but those of

A g 2 S e 1 ‐ x S x

(

0 ≤ x ≤ 0.5

) have not been investigated yet. Particularly, the relationship between crystalline structure and mechanical/TE performance for

A g 2 S e 1 ‐ x S x

solid solution is still unclear so far.

In this study, a series of polycrystalline

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, 0.2, 0.3, 0.4, and 0.45) samples were prepared. Their crystalline structures, mechanical properties, and TE properties were systematically investigated.

x = 0.3

in the

A g 2 S e 1 ‐ x S x

system was identified to be the transition boundary of the orthorhombic structure and monoclinic structure. Orthorhombic

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, and 0.2) samples are brittle, while monoclinic

A g 2 S e 1 ‐ x S x

(

x = 0.4

and 0.45) are ductile and flexible. Due to the stronger electron-phonon interaction, monoclinic Ag₂Se_0.6S_0.4 has lower PF and

z T

than orthorhombic

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, and 0.2). However, the superior TE performance and thermal stability to the organic TE materials and the intrinsically good flexibility still promise a great potential for monoclinic

A g 2 S e 1 ‐ x S x

to be used in wearable electronics.

2. 　Results and Discussion

Less

Figure 1(c) shows the X-ray diffraction patterns for the prepared

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, 0.2, 0.3, 0.4, and 0.45) obtained at room temperature. When the

S

content

x < 0.3

, the diffraction peaks are well indexed to the orthorhombic structure of Ag₂Se with the space group of

P 212121

. This indicates that Ag₂Se_0.9S_0.1 and Ag₂Se_0.8S_0.2 still adopt the same crystalline structure with Ag₂Se at room temperature. When

x = 0.4

and 0.45, the diffraction peaks agree well with the monoclinic structure of Ag₂S phase with the space group of

P 21 / n

. Likewise, the

A g 2 S e 1 ‐ x S x

(

x ≥ 0.5

) samples also crystalize in the same monoclinic structure of Ag₂S [21]. Elemental energy dispersive spectroscopy (EDS) mappings confirm that all elements are homogeneously distributed in Ag₂Se_0.9S_0.1, Ag₂Se_0.8S_0.2, Ag₂Se_0.6S_0.4, and Ag₂Se_0.55S_0.45. No obvious secondary phase is observed. Thus, these samples are phase pure. Likewise, scanning electron microscopy (SEM) performed on the cross-section of Ag₂Se_0.6S_0.4 indicates that it has an obvious layered structure (cf. Fig. S1).

One special composition in the

A g 2 S e 1 ‐ x S x

system is Ag₂Se_0.7S_0.3. As shown in Figure 1(c), its X-ray diffraction pattern looks like that of monoclinic Ag₂Se_0.6S_0.4. However, besides those belonging to the monoclinic structure, some extra diffraction peaks with weak intensities are also observed, such as (102) at

2 θ = 31 °

and (112) at

2 θ = 34 °

(right panel in Figure 1(c)). These are indexed to the orthorhombic structure. Thus, Ag₂Se_0.7S_0.3 is believed to be a mixture rather than a pure phase, in which the main phase crystalizes in the monoclinic structure while the secondary phase crystalizes in the orthorhombic structure. This result is different from that proposed by Bindi and Pingitore [33] that Ag₂Se_0.7S_0.3 crystalizes in the same orthorhombic structure with Ag₂Se. Figure 1(d) shows the EDS mappings performed on Ag₂Se_0.7S_0.3. Surprisingly, all elements are still homogeneously distributed. Thus, it is concluded that the two different phases in Ag₂Se_0.7S_0.3 have very similar chemical compositions but different crystalline structures. A similar polymorphic feature has been also observed in the

C u 2 S e 1 ‐ x S x

system [34]. Combining the above result, it can be concluded that the transition boundary between the monoclinic and orthorhombic structures in

A g 2 S 1 ‐ x S e x

solid solution should be around

x = 0.3

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, 0.2, 0.3, 0.4, and 0.45) samples possess structure-dependent mechanical properties. The three-point bending test and Vickers hardness test were performed on

A g 2 S e 1 ‐ x S x

. The material with larger bending deformation or small Vickers hardness is usually a benefit for the application in flexible electronics [2, 3, 6]. Figure 2(a) shows that orthorhombic Ag₂Se can only endure a very small bending strain before cracking. The maximum bending deformation is about 0.56%. Likewise, orthorhombic Ag₂Se_0.9S_0.1 also possesses a maximum bending deformation around 1.5%. The case is different for monoclinic Ag₂Se_0.6S_0.4, which exhibits a bending deformation above 10% without cracking. Previously, large bending deformation was also observed for monoclinic

A g 2 S e 1 ‐ x S x

(

x = 0.5

, 0.7, 0.9, and 1) in the bending test. It should be noted that such deformation is plastic, which is different from the elastic deformation of brittle materials with low dimension. Likewise, Vickers hardness for orthorhombic Ag₂Se is 43.7 Hv at room temperature. It is monotonously increased to 51.5 Hv and 62.7 Hv for the orthorhombic Ag₂Se_0.9S_0.1 and Ag₂Se_0.8S_0.2, respectively. However, monoclinic Ag₂Se_0.6S_0.4 has low Vickers hardness of only 33.8 Hv, about half of that for orthorhombic Ag₂Se_0.8S_0.2. As shown in Figure 2(c), Ag₂Se_0.6S_0.4 can be directly cut into thin strips with thickness about 0.1 mm like metal. Furthermore, these metal-like strips can be twisted into various shapes without cracking, confirming that Ag₂Se_0.6S_0.4 has good ductility and flexibility.

The above test results prove that the monoclinic structure has significantly better ductility and flexibility in the

A g 2 S e 1 ‐ x S x

system. The high cleavage energy and low slipping energy, related to the unique wrinkled layer structure, are the fundamental reason for the good ductility observed in monoclinic

A g 2 S e 1 ‐ x S x

. Previous investigation found that the S atoms in monoclinic Ag₂S always bonded to part of the surrounding Ag atoms during slipping [22, 35], which is benefit for preventing the material’s cleavage under mechanical stress. Likewise, it enables the bonding energy between Ag and S atoms to change fluently, yielding a low energy barrier for slipping. However, in the orthorhombic structure, such unique wrinkled layer structure does not exist; thus, the orthorhombic

A g 2 S e 1 ‐ x S x

samples are brittle. Here, it should be noted that although the main phase in Ag₂Se_0.7S_0.3 crystalizes in the monoclinic structure, Ag₂Se_0.7S_0.3 still has low maximum bending deformation around 0.88%. The reason should be attributed to the presence of brittle orthorhombic grains among the ductile monoclinic grains. The second phase strengthening effect caused by these brittle orthorhombic grains will impede the movement of atoms, dislocations, or interfaces under mechanical stress like that in the pure orthorhombic phase, yielding poor ductility for Ag₂Se_0.7S_0.3.

Figure 3 shows the measured

σ

and

α

for

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, 0.2, 0.3, 0.4, and 0.45). All samples possess negative

α

, indicating that they are

n

-type semiconductors with electrons dominating the electrical transports. This scenario is the same with those

A g 2 S e 1 ‐ x S x

(

x ≥ 0.5

) samples. Obvious

σ

and

α

discontinuous jumps are observed between 360 K and 420 K, which are attributed to the orthorhombic-cubic or monoclinic-cubic phase transition. For example, Ag₂Se experiences orthorhombic-cubic phase transition around 410 K. At 300 K,

σ

for Ag₂Se is about

1.4 × 105

S·m^-1. It increases with increasing temperature, reaching around

3.1 × 105

S·m^-1 at 403 K, and then decreases to

1.9 × 105

S·m^-1 after the phase transition. The

σ

value for Ag₂Se_0.55S_0.45 at 300 K is only

3.6 × 104

S·m^-1, almost one-fourth of the pristine Ag₂Se. Likewise, the

α

values vary from -146 μV·K^-1 to -105 μV·K^-1 at 300 K and from -45 μV·K^-1 to -109 μV·K^-1 at 420 K, without obvious chemical composition dependence. Furthermore, Fig. S2 shows that the prepared samples have good reproducibility. When the chemical composition and fabrication process are fixed, different batches of samples have comparable

σ

and

α

data.

With the purpose to understand the electrical transport properties of

A g 2 S e 1 ‐ x S x

, Hall measurements were performed. The Hall carrier concentration (

n H

) and mobility (

μ H

) at 300 K are listed in Table SI. All

A g 2 S e 1 ‐ x S x

samples possess

n H

in the order of 10¹⁸ cm^-3. However, being similar with the above measured

σ

and

α

, the

n H

values do not have monotonous variation with the sulfur content. The different contents of intrinsic defects inside the lattice, such as Ag interstitials, are expected to be the reason for this scenario. Likewise, the

μ H

values for the

A g 2 S e 1 ‐ x S x

samples are in the range of 309 cm²·V^-1·s^-1 to 1337 cm²·V^-1·s^-1. These

μ H

values are quite high as compared with other state-of-the-art TE materials, such as 190 cm²·V^-1·s^-1 for

n

-type Bi₂Te₃ [36] and 48 cm²·V^-1·s^-1 for

n

-type filled skutterudites [37]. A single parabolic model (SPB) is used to further understand the electrical transports of

A g 2 S e 1 ‐ x S x

. According to the SPB model, the Seebeck coefficient, carrier concentration, and carrier mobility can be correlated as follows [38–40]:

(1) α = κ B e 2 + λ F λ + 1 η 1 + λ F λ η − η, (2) n H = 4 π 2 m ∗ k B T h 2 3 / 2 F 1 / 2 η r H, (3) μ H = 3 π 4 1 / 2 + 2 λ 1 + λ 1 Γ 2 + λ F 2 λ − 1 / 2 F λ μ ph, (4) μ ph = 8 π 1 / 2 e ℏ 4 ρ v l 2 3 k B T 3 / 2 m ∗ 5 / 2 Ξ 2, (5) r H = 34 F 1 / 2 η F − 1 / 2 η F 0 2 η,

where

k B

is the Boltzmann constant,

λ

is the scattering factor,

e

is the electron charge,

m ∗

is the density-of-state effective mass,

r H

is the Hall factor,

ρ

is the sample density,

v l

is the velocity of longitudinal sound waves,

μ ph

is the drift mobility for acoustic phonon scattering in the nondegenerate limit, and Ξ is the deformation potential.

F m η

is the Fermi integrals, and it is given by equation

F m η = ∫ 0 ∞ x m d x / 1 + e x − η

, where

x

represents the reduced carrier energy and

η = E F / k B T

is the reduced Fermi energy.

Figure 3(d) presents that the

α

and

n H

data for the present

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, 0.2, 0.3, 0.4, and 0.45) samples roughly fall around the calculated theoretical Pisarenko curve with

m ∗ = 0.25 m e

(

m e

is the mass of free electron) and

λ = 0

(acoustic phonon scattering). For comparison, the previously reported data for Ag₂Se and Ag₂Se_0.5S_0.5 are also summarized in Figure 3(d). These data also fall around the theoretical curve. This scenario suggests that all these samples might possess a similar band structure near the Fermi level, despite the fact that some of them crystalize in the monoclinic structure while others in the orthorhombic structure. This is possible because the conduction band minimums of Ag₂S and Ag₂Se are at the same gamma point and both of them are mainly dominated by Ag-5s electrons [21, 41]. Alloying S at the Se sites would mainly alter the valence band maximum instead of the conduction band minimum, yielding the similar

m ∗

mentioned above. In addition, the small

m ∗

, about

0.25 m e

for these Ag₂(S,Se) samples, are responsible for their higher

μ H

than those for

n

-type Bi₂Te₃ [36] and filled skutterudites [37] mentioned above.

Figure 3(e) plots the

μ H

and

n H

relationship at 300 K for

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, 0.2, 0.4, 0.45, and 0.5). The data for Ag₂Se_0.7S_0.3 are not included because its polymorphic feature might introduce extra boundary scattering to electrons and interrupt the understanding on the carrier mobility. As shown in Figure 3(e), under the similar

n H

, the

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, and 0.2) samples with an orthorhombic structure have higher

μ H

than the

A g 2 S e 1 ‐ x S x

(

x = 0.4

, 0.45, and 0.5) samples with a monoclinic structure. By fitting the experimental data of the

μ H

and

n H

relationship using Equations (1)–(5), deformation potential values of 11 eV and 19 eV can be extracted for the orthorhombic

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, and 0.2) and the monoclinic

A g 2 S e 1 ‐ x S x

(0.4, 0.45, and 0.5), respectively. The thermal vibrations of the crystal lattice can influence the energy-band structure and perturb the carrier transports. The intensity of such interaction between electrons and phonons can be reflected by the magnitude of Ξ [42]. The lower Ξ value for the orthorhombic

A g 2 S e 1 ‐ x S x

suggests that the electron-phonon interaction wherein is weaker than that in the monoclinic

A g 2 S e 1 ‐ x S x

. This is responsible for the higher

μ H

observed for the orthorhombic

A g 2 S e 1 ‐ x S x

The power factors (PF) for

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, 0.2, 0.3, 0.4, and 0.45) samples calculated from the formula

PF = α 2 · σ

are shown in Figure 3(c). At 300 K, the PF value for Ag₂Se reaches 22.5 μW·cm^-1·K^-2. It gradually decreases with increasing the S-alloying content. At 300 K, the PF for Ag₂Se_0.55S_0.45 is just 5.2 μW·cm^-1·K^-2, about one-fourth of that for Ag₂Se. The greatly reduced

σ

is responsible for the lowered PF. The PF value for Ag₂Se_0.6S_0.4 is comparable with that for Ag₂Se_0.5S_0.5 reported before [21, 24], about 4.8 μW·cm^-1·K^-2 at 300 K. Based on the SPB model, the theoretical PF vs.

n H

curves at 300 K can be obtained for the orthorhombic and monoclinic

A g 2 S e 1 ‐ x S x

samples, respectively. As shown in Figure 3(f), the experimental PF and

n H

data basically fall around these lines. Under the comparable

n H

, the PF for the orthorhombic

A g 2 S e 1 ‐ x S x

samples are much higher than those of the monoclinic

A g 2 S e 1 ‐ x S x

samples. The reason is that the orthorhombic samples have weaker electron-phonon interaction than the monoclinic samples, which yields lower Ξ value for higher

μ H

and PF. In addition, based on the SPB model, the optimal carrier concentration (

n opt, PF

) corresponding to the peak PF is around

3 ‐ 4 × 1018

cm^-3 for both orthorhombic and monoclinic

A g 2 S e 1 ‐ x S x

n H

for the present orthorhombic

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, and 0.2) and monoclinic

A g 2 S e 1 ‐ x S x

(

x = 0.4

) samples are already close to this

n opt, PF

value.

Figure 4(a) shows

κ

as a function of temperature for

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, 0.2, 0.3, 0.4, and 0.45). The discontinuous jumps on the

κ

curves are attributed to the orthorhombic-cubic or monoclinic-cubic phase transitions.

κ

ranges from 0.7 W·m^-1·K^-1 to 1.4 W·m^-1·K^-1 for all samples. Ag₂Se_0.6S_0.4 exhibits the lowest

κ

among all samples.

κ

for Ag₂Se_0.6S_0.4 at 300 K is around 0.7 W·m^-1·K^-1. This value is about 36% decrement as compared with that for Ag₂Se_0.8S_0.2. Generally,

κ

is composed of two parts: the electron part

κ e

and the lattice part

κ L

κ e

can be calculated according to the Wiedemann-Franz law [43]. Figure 4(b) shows the calculated

κ e / κ

for

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, 0.2, 0.3, 0.4, and 0.45). It can be seen that the

κ e / κ

values are in the range of 48% to 80%, indicating that the carriers’ contribution is very important in the thermal transports. By subtracting

κ e

from

κ

κ L

can be obtained. The results at 300 K are listed in Table SI. They range from 0.20 W·m^-1·K^-1 to 0.48 W·m^-1·K^-1, which are very low values as compared with those for the state-of-the-art TE materials [44–49]. The proximity to the cubic superionic phase is responsible for the low

κ L

values observed in these orthorhombic and monoclinic phases [23].

Based on the measured

α

σ

, and

κ

z T

can be calculated according to

z T = α 2 σ T / κ .

z T

for orthorhombic Ag₂Se is around 0.6 in the whole measured temperature range, which is comparable with those reported before [28–30]. Orthorhombic Ag₂Se_0.9S_0.1 and Ag₂Se_0.8S_0.2 possess comparable

z T s

with Ag₂Se. However,

z T s

for monoclinic Ag₂Se_0.6S_0.4 and Ag₂Se_0.55S_0.45 are much lower than those for orthorhombic Ag₂Se. At 300 K,

z T

is just 0.26 for Ag₂Se_0.6S_0.4 and 0.23 for Ag₂Se_0.55S_0.45.

As shown in Figure 4(d), the theoretical

z T

vs.

n H

curves for orthorhombic and monoclinic

A g 2 S e 1 ‐ x S x

samples at 300 K are given by assuming that all samples possess the same

κ L = 0.4

W m^-1 K^-1. The experimental

z T

and

n H

data basically fall around these lines. Under the comparable

n H

z T

for the orthorhombic

A g 2 S e 1 ‐ x S x

samples is much higher than that of the monoclinic

A g 2 S e 1 ‐ x S x

samples because their weaker electron-phonon interaction yields lower Ξ value and larger

μ H

for higher PF. The optimal carrier concentration (

n opt, z T

) corresponding to the peak

z T

is around

1 ‐ 2 × 1018

cm^-3 for orthorhombic

A g 2 S e 1 ‐ x S x

, while

2 ‐ 3 × 1018

cm^-3 for monoclinic

A g 2 S e 1 ‐ x S x

n H

for the present orthorhombic

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, and 0.2) and monoclinic

A g 2 S e 1 ‐ x S x

(

x = 0.4

, 0.45, and 0.5) samples are still higher than these

n opt, z T

values. Thus, if their carrier concentration can be further reduced, higher

z T

can be expected.

Although the TE performances for ductile monoclinic

A g 2 S e 1 ‐ x S x

are lower than those for brittle orthorhombic

A g 2 S e 1 ‐ x S x

, their performances are still much higher than those for the organic TE materials reported before. This can be clearly reflected by the scenario shown in Figure 5. The PF values for most of the

n

-type TE organic TE materials are lower than 1 μW·cm^-1·K^-2 at 300 K. Even for the best

n

-type TE organic TE materials reported so far, poly(Ni-ett) [19], its PF, 3.6 μW·cm^-1·K^-2 at 300 K, is still lower than the present monoclinic

A g 2 S e 1 ‐ x S x

. The superior PF values achieved in the monoclinic

A g 2 S e 1 ‐ x S x

samples would promise high power output when they are fabricated into TE devices. In addition, most

n

-type organic TE materials are unstable in the air because their electron affinity is too low to stabilize the

n

-type dopants [2, 50]. In contrast, the present ductile monoclinic

A g 2 S e 1 ‐ x S x

samples are inert to oxygen or water; thus, they can realize good service stability in real application. Combining the intrinsically good flexibility and ductility, these monoclinic

A g 2 S e 1 ‐ x S x

samples show great potential to be used in wearable electronics.

3. 　Conclusion

Less

In summary, this study systematically studied the crystalline structure, mechanical properties, and TE properties of

A g 2 S e 1 ‐ x S x

(

x = 0

, 0.1, 0.2, 0.3, 0.4, and 0.45).

A g 2 S e 1 ‐ x S x

samples crystalize in the orthorhombic structure when

x ≤ 0.2

, while in the monoclinic structure when

x ≥ 0.4

. Only the monoclinic

A g 2 S e 1 ‐ x S x

samples possess good ductility and flexibility. Under comparable carrier concentration range, the orthorhombic

A g 2 S e 1 ‐ x S x

samples have higher carrier mobility, larger power factor, and better

z T

than the monoclinic samples because they have weaker electron-phonon interaction. This leads to lower

z T

values of monoclinic

A g 2 S e 1 ‐ x S x

(

x = 0.4

and 0.45) samples than those of the orthorhombic

A g 2 S e 1 ‐ x S x

(

x = 0.1

and 0.2) samples. However, the higher PF and better thermal stability promise a great potential for monoclinic

A g 2 S e 1 ‐ x S x

to be used in wearable electronics.

Funding

Less

Vetenskapsrådet(2018-06030)
Shanghai Rising-Star Program(19QA1410200)
Youth Innovation Promotion Association of the Chinese Academy of Sciences(2016232)
National Natural Science Foundation of China(5181101519; 91963208; 51625205)
National Key Research and Development Program of China(2018YFB0703600)
Chinese Academy of Sciences(121631KYSB20180060)

References

Less

Jin

, Li

, Iocozzia

, Zeng

, Wei

P. C.

, Yang

, Li

, Liu

, He

J. H.

, Zhu

, Wang

, Lin

, and Wang

, “Hybrid organic–inorganic thermoelectric materials and devices,” Angewandte Chemie International Edition, vol. 58, no. 43, pp. 15206–15226, 2019

Wang

, Yang

, Shi

X. L.

, Shi

, Chen

, Dargusch

M. S.

, Zou

, and Chen

Z. G.

, “Flexible thermoelectric materials and generators: challenges and innovations,” Advanced Materials, vol. 31, no. 29, article 1807916, 2019

Yang

J. C.

, Mun

, Kwon

S. Y.

, Park

, Bao

, and Park

, “Electronic skin: recent progress and future prospects for skin-attachable devices for health monitoring, robotics, and prosthetics,” Advanced Materials, vol. 31, no. 48, article e1904765, 2019

Jiang

, and Tian

, “Inorganic semiconductor biointerfaces,” Nature Reviews Materials, vol. 3, no. 12, pp. 473–490, 2018

Yao

, Fan

, Cheng

, Guan

, Wang

, Sun

, and Ouyang

, “Recent development of thermoelectric polymers and composites,” Macromolecular Rapid Communications, vol. 39, no. 6, article e1700727, 2018

Lim

H. R.

, Kim

H. S.

, Qazi

, Kwon

Y. T.

, Jeong

J. W.

, and Yeo

W. H.

, “Advanced soft materials, sensor integrations, and applications of wearable flexible hybrid electronics in healthcare, energy, and environment,” Advanced Materials, vol. 32, no. 15, article e1901924, 2020

Snyder

G. J.

, Lim

J. R.

, Huang

C.-K.

, and Fleurial

J.-P.

, “Thermoelectric microdevice fabricated by a MEMS-like electrochemical process,” Nature Materials, vol. 2, no. 8, pp. 528–531, 2003

Kim

S. J.

, We

J. H.

, and Cho

B. J.

, “A wearable thermoelectric generator fabricated on a glass fabric,” Energy & Environmental Science, vol. 7, no. 6, pp. 1959–1965, 2014

Kim

S. J.

, Lee

H. E.

, Choi

, Kim

, We

J. H.

, Shin

J. S.

, Lee

K. J.

, and Cho

B. J.

, “High-performance flexible thermoelectric power generator using laser multiscanning lift-off process,” ACS Nano, vol. 10, no. 12, pp. 10851–10857, 2016

Nan

, Kang

S. D.

, Li

, Yu

K. J.

, Zhu

, Wang

, Dunn

A. C.

, Zhou

, Xie

, Agne

M. T.

, Wang

, Luan

, Zhang

, Huang

, Snyder

G. J.

, and Rogers

J. A.

, “Compliant and stretchable thermoelectric coils for energy harvesting in miniature flexible devices,” Science Advances, vol. 4, no. 11, article eaau5849, 2018

Kim

, Kwon

, Eom

, Lee

J. E.

, Park

, Jo

, Park

S. H.

, Kim

B. S.

, Im

H. J.

, Lee

M. H.

, Min

T. S.

, Kim

K. T.

, Chae

H. G.

, King

W. P.

, and Son

J. S.

, “3D printing of shape-conformable thermoelectric materials using all- inorganic Bi₂Te₃-based inks,” Nature Energy, vol. 3, no. 4, pp. 301–309, 2018

Feng

, Tang

, Zhang

, and Wang

, “Flexible, high-power density, wearable thermoelectric nanogenerator and self-powered temperature sensor,” ACS Applied Materials & Interfaces, vol. 11, no. 42, pp. 38616–38624, 2019

Pan

, Qiu

, Witting

, Zhang

, Fu

, Li

J. W.

, Huang

, Sun

F. H.

, He

, Snyder

G. J.

, Felser

, and Li

J. F.

, “Synergistic modulation of mobility and thermal conductivity in (Bi,Sb)₂ Te₃ towards high thermoelectric performance,” Energy & Environmental Science, vol. 12, no. 2, pp. 624–630, 2019

Qiu

, Yan

, Luo

, Tang

, Yao

, Zhang

, Su

, Tan

, Xie

, Kanatzidis

M. G.

, Uher

, and Tang

, “3D printing of highly textured bulk thermoelectric materials: mechanically robust BiSbTe alloys with superior performance,” Energy & Environmental Science, vol. 12, no. 10, pp. 3106–3117, 2019

Bubnova

, Khan

Z. U.

, Malti

, Braun

, Fahlman

, Berggren

, and Crispin

, “Optimization of the thermoelectric figure of merit in the conducting polymer poly(3,4-ethylenedioxythiophene),” Nature Materials, vol. 10, no. 6, pp. 429–433, 2011

Sun

, Sheng

, di

, Jiao

, Xu

, Qiu

, and Zhu

, “Organic thermoelectric materials and devices based on p- and n-type poly(metal 1,1,2,2-ethenetetrathiolate)s,” Advanced Materials, vol. 24, no. 7, pp. 932–937, 2012

Kim

G. H.

, Shao

, Zhang

, and Pipe

K. P.

, “Engineered doping of organic semiconductors for enhanced thermoelectric efficiency,” Nature Materials, vol. 12, no. 8, pp. 719–723, 2013

Zhang

, Sun

, Xu

, and Zhu

, “What to expect from conducting polymers on the playground of thermoelectricity: lessons learned from four high-mobility polymeric semiconductors,” Macromolecules, vol. 47, no. 2, pp. 609–615, 2014

Sun

, Qiu

, Tang

, Geng

, Wang

, Zhang

, Huang

, Xu

, Yue

, Guan

Y. S.

, Jiao

, Sun

, Tang

, di

C. A.

, Yi

, and Zhu

, “Flexible n-type high-performance thermoelectric thin films of poly(nickel-ethylenetetrathiolate) prepared by an electrochemical method,” Advanced Materials, vol. 28, no. 17, pp. 3351–3358, 2016

Zhang

, Sun

, Qin

, Xu

, and Zhu

, “Two soluble polymers with lower ionization potentials: doping and thermoelectric properties,” Journal of Materials Chemistry A, vol. 4, no. 4, pp. 1432–1439, 2016

Liang

, Wang

, Qiu

, Yang

, Ming

, Chen

, Song

, Zhao

, Wei

T. R.

, Ren

, Sun

Y. Y.

, Shi

, He

, and Chen

, “Flexible thermoelectrics: from silver chalcogenides to full-inorganic devices,” Energy & Environmental Science, vol. 12, no. 10, pp. 2983–2990, 2019

Shi

, Chen

, Hao

, Liu

, Wang

, Qiu

, Burkhardt

, Grin

, and Chen

, “Room-temperature ductile inorganic semiconductor,” Nature Materials, vol. 17, no. 5, pp. 421–426, 2018

Tuo

, Hong-Yi

, Peng-Fei

, Xun

, and Li-Dong

, “Thermoelectric properties of Ag₂S superionic conductor with intrinsically low lattice thermal conductivity,” Acta Physica Sinica, vol. 68, no. 9, article 90201, 2019

Wang

, Zhao

, Qiu

, Song

, Chen

, and Shi

, “Aguilarite Ag₄SSe thermoelectric material: natural mineral with low lattice thermal conductivity,” ACS Applied Materials & Interfaces, vol. 11, no. 13, pp. 12632–12638, 2019

, Li

, Liu

, Jiang

, Feng

, Zhu

, Zhang

, Dong

, Deng

, Luo

, Zhang

, and Chen

, “Semiconductor glass with superior flexibility and high room temperature thermoelectric performance,” Science Advances, vol. 6, no. 15, article eaaz8423, 2020

Lee

, Park

Y.-H.

, and Hashimoto

, “Effect of nonstoichiometry on the thermoelectric properties of a Ag₂Se alloy prepared by a mechanical alloying process,” Journal of Applied Physics, vol. 101, no. 2, article 024920, 2007

Aliev

F. F.

, Jafarov

M. B.

, and Eminova

V. I.

, “Thermoelectric figure of merit of Ag₂Se with Ag and Se excess,” Semiconductors, vol. 43, no. 8, pp. 977–979, 2009

Day

, Drymiotis

, Zhang

, Rhodes

, Shi

, Chen

, and Snyder

G. J.

, “Evaluating the potential for high thermoelectric efficiency of silver selenide,” Journal of Materials Chemistry C, vol. 1, no. 45, pp. 7568–7573, 2013

, Qiu

, Zhang

, Lv

, Shi

, and Chen

, “Thermoelectric transport of Se-rich Ag₂Se in normal phases and phase transitions,” Applied Physics Letters, vol. 104, no. 13, article 133903, 2014

Yang

, Su

, Meng

, Wang

, Yan

, Yang

, He

, Zhang

, Uher

, Kanatzidis

M. G.

, and Tang

, “Facile room temperature solventless synthesis of high thermoelectric performance Ag₂Se via a dissociative adsorption reaction,” Journal of Materials Chemistry A, vol. 5, no. 44, pp. 23243–23251, 2017

Ding

, Qiu

, Cai

, Yao

, Chen

, and He

, “High performance n-type Ag₂Se film on nylon membrane for flexible thermoelectric power generator,” Nature Communications, vol. 10, no. 1, p. 841, 2019

, Qiu

, Cai

, Ding

, Wang

, Jiang

, Yao

, Huang

, Chen

, and He

, “Ultrahigh power factor and flexible silver selenide-based composite film for thermoelectric devices,” Energy & Environmental Science, vol. 13, no. 4, pp. 1240–1249, 2020

Bindi

, and Pingitore

N. E.

, “On the symmetry and crystal structure of aguilarite, Ag₄SeS,” Mineralogical Magazine, vol. 77, no. 1, pp. 21–31, 2013

Zhao

, Blichfeld

A. B.

, Eikeland

, Qiu

, Ren

, Iversen

B. B.

, Shi

, and Chen

, “Extremely low thermal conductivity and high thermoelectric performance in liquid-like Cu₂Se_1−xS_x polymorphic materials,” Journal of Materials Chemistry A, vol. 5, no. 34, pp. 18148–18156, 2017

, An

, Morozov

S. I.

, Duan

, Goddard W. A. III, Zhang

, Zhai

, and Snyder

G. J.

, “Ductile deformation mechanism in semiconductor α-Ag₂S,” npj Computational Materials, vol. 4, no. 1, 2018

Hao

, Xing

, Qiu

, Hu

, Wei

, Ren

, Shi

, and Chen

, “Enhanced thermoelectric performance in n-type Bi₂Te₃-based alloys via suppressing intrinsic excitation,” ACS Applied Materials & Interfaces, vol. 10, no. 25, pp. 21372–21380, 2018

Shi

, Yang

, Salvador

J. R.

, Chi

, Cho

J. Y.

, Wang

, Bai

, Yang

, Zhang

, and Chen

, “Multiple-filled skutterudites: high thermoelectric figure of merit through separately optimizing electrical and thermal transports,” Journal of the American Chemical Society, vol. 133, no. 20, pp. 7837–7846, 2011

Goldsmid

H. J.

Introduction to Thermoelectricity, Springer, Berlin, vol. 121, 2010

Xie

, Wang

, Pei

, Fu

, Liu

, Snyder

G. J.

, Zhao

, and Zhu

, “Beneficial contribution of alloy disorder to electron and phonon transport in half-Heusler thermoelectric materials,” Advanced Functional Materials, vol. 23, no. 41, pp. 5123–5130, 2013

Zhao

, Blichfeld

A. B.

, Chen

, Song

, Zhang

, Zhu

, Ren

, Hanus

, Qiu

, Iversen

B. B.

, Xu

, Snyder

G. J.

, Shi

, and Chen

, “Enhanced thermoelectric performance through tuning bonding energy in Cu₂Se_1–xS_x Liquid-like materials,” Chemistry of Materials, vol. 29, no. 15, pp. 6367–6377, 2017

Fang

C. M.

, de Groot

R. A.

, and Wiegers

G. A.

, “Ab initio band structure calculations of the low-temperature phases of Ag₂Se, Ag₂Te and Ag₃AuSe₂,” Journal of Physics and Chemistry of Solids, vol. 63, no. 3, pp. 457–464, 2002

Nolas

G. S.

, Sharp

, and Goldsmid

Thermoelectrics: Basic Principles and New Materials Developments, Springer Science & Business Media, vol. 45, 2013

Kim

H. S.

, Gibbs

Z. M.

, Tang

, Wang

, and Snyder

G. J.

, “Characterization of Lorenz number with Seebeck coefficient measurement,” APL Materials, vol. 3, no. 4, 2015

Shuai

, Ge

, Mao

, Song

, Wang

, and Ren

, “Significant role of Mg stoichiometry in designing high thermoelectric performance for Mg₃(Sb,Bi)₂-based n-type Zintls,” Journal of the American Chemical Society, vol. 140, no. 5, pp. 1910–1915, 2018

Liu

, Mao

, Sui

, and Ren

, “High thermoelectric performance of α-MgAgSb for power generation,” Energy & Environmental Science, vol. 11, no. 1, pp. 23–44, 2018

Chen

, Zhang

, and Pei

, “Manipulation of phonon transport in thermoelectrics,” Advanced Materials, vol. 30, no. 17, article e1705617, 2018

, Xin

, Zhu

, Shen

, Fang

, and Zhao

, “Approaching the minimum lattice thermal conductivity of p-type SnTe thermoelectric materials by Sb and Mg alloying,” Science Bulletin, vol. 64, no. 14, pp. 1024–1030, 2019

Chang

, and Zhao

L.-D.

, “Anharmoncity and low thermal conductivity in thermoelectrics,” Materials Today Physics, vol. 4, pp. 50–57, 2018

Wang

, Xiong

, Wang

, Qiu

, Song

, Zhao

, Yang

, Xiao

, Shi

, and Chen

, “Cu₃ErTe₃: a new promising thermoelectric material predicated by high-throughput screening,” Materials Today Physics, vol. 12, article 100180, 2020

Wang

, Sun

, Ail

, Vagin

, Persson

P. O. Å.

, Andreasen

J. W.

, Thiel

, Berggren

, Crispin

, Fazzi

, and Fabiano

, “Thermoelectric properties of solution-processed n-doped ladder-type conducting polymers,” Advanced Materials, vol. 28, no. 48, pp. 10764–10771, 2016

Huang

, Yao

, Cui

, Zou

, Zhang

, Wang

, Shen

, Jin

, Zhu

, Diao

, Xu

, di

C. A.

, and Zhu

, “Conjugated-backbone effect of organic small molecules for n-type thermoelectric materials with ZT over 0.2,” Journal of the American Chemical Society, vol. 139, no. 37, pp. 13013–13023, 2017

Huewe

, Steeger

, Kostova

, Burroughs

, Bauer

, Strohriegl

, Dimitrov

, Woodward

, and Pflaum

, “Low-cost and sustainable organic thermoelectrics based on low-dimensional molecular metals,” Advanced Materials, vol. 29, no. 13, article 1605682, 2017

Yuan

, Huang

, Zhang

, Zou

, di

C. A.

, Zhu

, and Zhu

, “Efficient solution-processed n-type small-molecule thermoelectric materials achieved by precisely regulating energy level of organic dopants,” ACS Applied Materials & Interfaces, vol. 9, no. 34, pp. 28795–28801, 2017

Appendix

Less

Year 2020 volume 2020 Issue 7

PDF

Cite this Article

BibTeX

Article Info

doi: 10.34133/2020/6591981

Receive Date：2020-04-21
Online Date：2026-10-27
Published：2020-07-20

Article Data

Affiliations

History

Received：2020-04-21
Accepted：2020-06-17

Funding

Vetenskapsrådet(2018-06030)

Shanghai Rising-Star Program(19QA1410200)

Youth Innovation Promotion Association of the Chinese Academy of Sciences(2016232)

National Natural Science Foundation of China(5181101519; 91963208; 51625205)

National Key Research and Development Program of China(2018YFB0703600)

Chinese Academy of Sciences(121631KYSB20180060)

Affiliations

¹State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China

²Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China

³Division of Solid-State Electronics, Department of Electrical Engineering, Uppsala University, Uppsala, Sweden

⁴School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China

References

Share

https://castjournals.cast.org.cn/joweb/research/EN/10.34133/2020/6591981

Share to

A g 2 S e 1 ‐ x S x

System">

A g 2 S e 1 ‐ x S x

System&url=https://castjournals.cast.org.cn/joweb/research/EN/10.34133/2020/6591981">

Scan QR to access full text

Cite this article

BibTeX

Citations

表12种不同金属材料的力学参数

科 Family	属数 Number of genus	种数 Number of species	占总种数比例 Percentage of total species (%)	属 Genus	种数 Number of species	占总种数比例 Percentage of total species (%)
鹅膏菌科Amanitaceae	2	11	5.26	鹅膏菌属 Amanita	10	4.78
小菇科 Mycenaceae	2	12	5.74	丝盖伞属 Inocybe	5	2.39
多孔菌科 Polyporaceae	8	14	6.70	蜡蘑属 Laccaria	5	2.39
红菇科 Russulaceae	3	23	11.00	小皮伞属 Marasmius	6	2.87
				小菇属 Mycena	11	5.26
				光柄菇属 Pluteus	5	2.39
				红菇属 Russula	17	8.13
				栓菌属 Trametes	5	2.39

关闭全屏

BibTeX
EndNote
RefWorks
TxT

Figure 1: Crystalline structures for (a) monoclinic Ag₂S and (b) orthorhombic Ag₂Se. (c) Room-temperature X-ray diffraction patterns for $A g 2 S e 1 ‐ x S x$ ( $x = 0$ , 0.1, 0.2, 0.3, 0.4, and 0.45) samples. The right panel shows the magnification around $2 θ = 30 ~ 35 °$ . (d) Backscatter electron (AsB) image and elemental energy dispersive spectroscopy (EDS) mappings of Ag₂Se_0.7S_0.3.

Figure 2: (a) Strain-stress curves for the three-point bending test of $A g 2 S e 1 ‐ x S x$ ( $x = 0$ , 0.1, 0.3, and 0.4) samples at 300 K. The tests were performed by using a dynamic mechanical analyzer (DMA). The insets show the optical images of Ag₂Se_0.6S_0.4 sample before and after the bending test. The data for Ag₂S are included for comparison [22]. (b) Vickers hardness of $A g 2 S e 1 ‐ x S x$ under the load of 0.3 kgf. The insets are micrographs of indention. Vickers hardness of Ag₂S reported in Ref. 22 is included for comparison. (c) Ag₂Se_0.6S_0.4 strips twisted into various shapes. The thickness of Ag₂Se_0.6S_0.4 strips is 0.1 mm.

Figure 3: Temperature dependences of (a) electrical conductivity $σ$ and (b) Seebeck coefficient $α$ for $A g 2 S e 1 ‐ x S x$ ( $x = 0$ , 0.1, 0.2, 0.3, 0.4, and 0.45). (c) Temperature dependence of power factor (PF) for $A g 2 S e 1 ‐ x S x$ ( $x = 0$ , 0.1, 0.2, 0.3, 0.4, and 0.45). (d) Seebeck coefficient $α$ , (e) Hall carrier mobility $μ H$ , and (f) PF as a function of carrier concentration $n H$ for $A g 2 S e 1 ‐ x S x$ at 300 K. The dashed lines represent the theoretical curves based on the single parabolic band (SPB) model with a dominated scattering mechanism by acoustic phonons. The data for Ag₂Se and Ag₂Se_0.5S_0.5 reported before are added for comparison [21, 26–29].

Figure 4: (a) Temperature dependence of thermal conductivity for $A g 2 S e 1 ‐ x S x$ ( $x = 0$ , 0.1, 0.2, 0.3, 0.4, and 0.45). (b) The ratio of electronic thermal conductivity to thermal conductivity ( $κ e / κ$ ) at 300 K for $A g 2 S e 1 ‐ x S x$ . (c) Temperature dependence of TE figure of merit $z T$ for $A g 2 S e 1 ‐ x S x$ ( $x = 0$ , 0.1, 0.2, 0.3, 0.4, and 0.45). (d) $z T$ as a function of carrier concentration $n H$ for $A g 2 S e 1 ‐ x S x$ at 300 K. The dashed lines represent the theoretical curves based on the single parabolic band (SPB) model. The data for Ag₂Se_0.5S_0.5 reported before are added for comparison.

Figure 5: Comparisons of power factor values for $n$ -type monoclinic $A g 2 S e 1 ‐ x S x$ and $n$ -type organic TE materials reported before [16, 19, 51–53].

Articles: Latest Articles; Most Read; Collections

Updates: Events; News; Multimedia

About: About Us

Contact

No. 86 Xueyuan South Road, Haidian District, Beijing

100081

010-62662699(Operation and Technical Support)

qkjq@cast.org.cn

Copyright © 2025 China Association for Science and Technology. All rights reserved. For all open access content, the relevant licensing terms apply.
Sponsored by the Office of the Leading Group for Cybersecurity and Informatization of CAST, and supported by Science and Technology Review Publishing House