Fast Ag-Ion-Conducting GeS2âSb2S3âAgI Glassy Electrolytes with

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Fast Ag-Ion Conducting GeS2–Sb2S3–AgI Glassy Electrolytes with Exceptionally Low Activation Energy Changgui Lin, Erwei Zhu, Jingsong Wang, Xuhao Zhao, Feifei Chen, and Shixun Dai J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b10630 • Publication Date (Web): 09 Jan 2018 Downloaded from http://pubs.acs.org on January 9, 2018

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The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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The Journal of Physical Chemistry

Fast Ag-Ion Conducting GeS2–Sb2S3–AgI Glassy Electrolytes with Exceptionally Low Activation Energy Changgui Lin, †,‡,* Erwei Zhu,†,‡ Jingsong Wang,†,‡ Xuhao Zhao,†,‡ Feifei Chen,†,‡ Shixun Dai†,‡,* †

Laboratory of Infrared Materials and Devices, The Research Institute of Advanced

Technologies, Ningbo University, Ningbo 315211, P. R. China. ‡

Key Laboratory of Photoelectric Detection Materials and Devices of Zhejiang

Province, Ningbo 315211, P. R. China. *Corresponding author: [email protected] (C. Lin); [email protected] (S. Dai)

Abstract: Silver-ion conducting solid electrolytes with low activation energy are important because of their distinctive application potential in solid-state batteries operated within a broad temperature range, especially below room temperature. Achieving glassy solid electrolytes with high ionic conductivity, low activation energy, and good thermal stability is a continuous challenge for the design and synthesis of novel fast ion-conducting glasses. Here, we report markedly low activation energy and high room temperature ionic conductivity in melt-quenched GeS2–Sb2S3–AgI chalcogenide glasses. Homogeneous 2.5GeS2–27.5Sb2S3–70AgI glass presenting high glass transition temperature of 135 oC shows high ionic conductivity of 9.18×10−3 S/cm at 25 oC and low activation energy of 0.07 eV, which is the lowest among those of 1

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Ag-ion glassy electrolytes. Structural characterization by using Raman spectra suggests that in the disordered network structure of GeS2–Sb2S3–AgI glasses, the formation of chain fragments composed by [SbS3−xIx]n, which is similar to the double chain of [(SbSI)∞]2 in the SbSI crystal structure, provides possible diffusion pathways to facilitate low-barrier concerted migration of silver ions.

1. Introduction

Since the discovery of the superionic conduction of silver in the high-temperature phase of silver iodide (α-AgI), AgI-containing solid electrolytes have attracted widespread interest.1-3 The room-temperature (RT) ionic conductivity of AgI can increase rapidly from approximately 10−5 S·cm−1 to 1 S·cm−1, which is comparable with that of liquid electrolytes, when the low-temperature phase of β/γ-AgI transforms to α-AgI at 147 °C. Several successful efforts

4-7

have been focused to stabilize the

high-temperature phase α-AgI to room temperature. For example, secondary compounds can be added to form ternary phases with fast Ag-ion conduction, such as RbAg4I5,4 which has been used as a solid electrolyte in portable batteries for heart pacemaker.6 In addition, the α-→β-/γ-phase transition temperature can be suppressed to RT in AgI–Ag3BO3 glass matrices by applying rapid melt-quenching technique5 or polymer-coated AgI nanoparticles with controlled size and shape.7 Although a high conductivity of Ag+ of approximately 0.1 S·cm−1 can be achieved at RT, the crystalline nature and specific fabrication techniques of the above-mentioned

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AgI-based materials render the above-mentioned AgI-based materials difficult to use as solid electrolytes in certain promising flexible battery designs, such as thin film, roll-to-roll, and fiber textile batteries.8-10 The fast Ag-ion conducting glassy electrolyte, which possesses the advantages of compositional flexibility and easy fabrication of film or fiber, still needs to be improved to satisfy the requirement of future rechargeable batteries. Fast Ag-ion conducting glasses with high RT conductivity of 10−3–10−2 S·cm−1 have been synthesized in a variety of systems of oxides and chalcogenides.11-13 These electrolyte glasses are extensively studied; however, practical problems remain, including poor glass-forming ability and thermodynamic instability against phase separation.14,

15

Most of these materials are synthesized by rapid melt-quenching

(twin-roller quenching) or mechanical milling techniques and are found to be phase-separated intrinsically or after thermal cycling. The search for fast Ag-ion conducting glassy electrolytes with good chemical and thermodynamic stability, high homogeneity, and easy synthesis has become the subject of continued investigations.1, 3, 16, 17

Given the relatively high activation energy (normally >0.25 eV), the ionic conductivity of the previously reported Ag-ion glassy electrolytes substantially changes with temperature.11-13 Stable performance under changing temperature environments in a solid state device is a considerable challenge. Low activation energy in a material is crucial to achieve consistent performance of the device in a broad temperature range, especially below room temperature. 3



In this work, we report novel fast Ag-ion conducting glasses in the ternary system GeS2–Sb2S3–AgI; these glasses are stable against moisture attack under ambient condition, crystallization, and phase separation. Glasses with high AgI content of up to 70 mol% are fabricated by traditional melt-quenching technique within silica ampoules, and exhibit remarkable ionic conductivity of approximately 10−2 S·cm−1 at RT. These glassy electrolytes exhibit the lowest reported activation energy in silver superionic glassy conductors. Moreover, from the glass network structure established by Raman spectroscopy, we obtain an understanding of possible diffusion pathways for the Ag-ion in this system.

2. Experimental Section

Several samples of the nominal compositions xGeS2–ySb2S3–zAgI (x+y+z=1) (abbreviated as GxSAz) were prepared by quenching the melts in sealed silica ampoules (~10−3 Pa).2 The obtained samples were annealed, cut, and polished to obtain plate-like samples with diameter of 9 mm and thickness of 2 mm. The crystalline and amorphous characteristics of the as-prepared samples were confirmed by X-ray diffraction (XRD) measurement (Bruker D2 Phaser; 30 kV, 10 mA; CuKα). Calorimetric measurements were carried out by differential scanning calorimetry (DSC, TA Q2000 Thermal Analysis) at a heating rate of 10 °C/min with a temperature accuracy of ±1 °C. The characteristic temperatures of glass transition (Tg), onset crystallization (Tx), and other thermal transitions were obtained using the thermal analyzer microprocessor.

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For electrical measurements, gold electrodes with a diameter of 8 mm were sputtered on the parallel surfaces of the as-prepared samples. Electrical conductivity was measured using complex impedance technique with a frequency response analyzer (Zahner IM6). Ac impedance over a wide range of frequencies from 1 Hz to 8 MHz were measured between RT (~25 °C) and the temperature near Tg. Resistance (R) is determined by comparing the measured complex impedance to that simulated using an appropriated equivalent circuit. The equivalent circuit used is composed of a parallel RQ circuit, where R is a resistor and Q is a constant phase element. According to this equivalent circuit, electrical characteristics of the samples can be obtained. Raman spectra were measured at RT in a backscattering configuration using a Raman Spectrometer (Renishaw inVia). For preventing local laser damage, a 785-nm LD laser with a power of less than 1 mW was used as excitation source.

3. Results and Discussion

3.1. Glass Formation and Thermal Properties The glass formation and physical properties of GeS2–Sb2S3–AgI system were studied in our previous work.2 Here, we reinvestigated samples containing high AgI content selected for investigating fast Ag-ion conduction behavior and found that the glass-forming region of the GeS2–Sb2S3–AgI system can be further expanded. The expansion of this glass-forming region here is due to that we made a mistake in our previous study. 10GeS2–30Sb2S3–60AgI sample that was learned to be partially crystallized is found to be amorphous. Then, more AgI was added here, leading to

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explore a large glass-forming region. As shown in Fig. 1, a large AgI content reaching 70 mol% was dissolved successfully into the GeS2–Sb2S3 glassy matrix on high Sb2S3 content side. Notably, GeS2–Sb2S3–AgI system presents the largest melt-quenched glass-forming region among pseudo-ternary chalcohalide systems, including GeS2– Ga(In)2S3–MX (MX= metal halides, such as KI, CsCl, PbI2, AgI, and BaCl2),18-24 GeSe2–Ga2Se3–MX25, 26, and GeSe2–Sb2Se3–MX.27 The inset photos in Fig. 1 display the glassy and crystalline appearance of 2.5GeS2– 27.5Sb2S3–70AgI (G2.5SA70) and 10GeS2–20Sb2S3–70AgI (G10SA70) samples. Their amorphous and crystalline characteristics were confirmed by the XRD patterns as shown in Fig. 2a. The diffraction patterns of typical glass-ceramic samples outside the glass-forming region reveal that γ-AgI crystallites together with a small amount of β-AgI are precipitated. Sb2S3

0.0 1.0 0.2

glassy crystalline

0.8

0.4

0.6

0.6

0.4

0.8

AgI

0.2

1.0 0.0

0.0 0.2

0.4

0.6

0.8

1.0

GeS2

Figure 1. Glass-forming region of the GeS2–Sb2S3–AgI system. Inset shows the 2.5GeS2–27.5Sb2S3–70AgI glass and 10GeS2–20Sb2S3–70AgI glass-ceramic samples. The shadowed area is the glass-forming region reported previously.

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(a)

(b)

XRD intensity / a.u.

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G40SA50 G10SA70 G2.5SA70 γ-AgI

Heat flow / a.u.

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G40SA50 o

120 C o

147 C G10SA70 o

Tg=135 C G2.5SA70

β-AgI

o

Tx=214 C

10 20 30 40 50 60 70

50 100 150 200 250 300

2 theta / °

Temperature / °C

o

Figure 2 (a) XRD patterns of the as-prepared 2.5GeS2–27.5Sb2S3–70AgI (G2.5SA70), 10GeS2–20Sb2S3–70AgI (G10SA70), and 40GeS2–10Sb2S3–50AgI (G40SA50) samples, and standard β- and γ-AgI crystal phases (JCPDS #78-1616 and #9-399, respectively). (b) DSC curves of G2.5SA70, G10SA70, and G40SA50 samples. Thermal analysis of the as-prepared samples was performed through DSC measurements. As shown in Fig. 2b, the characteristic Tg and Tx for G2.5SA70 glass are determined as 135 °C and 214 °C, respectively. The heating and cooling DSC thermograms of G10SA70 and 40GeS2–10Sb2S3–50AgI (G40SA50) samples were recorded in Fig. 2b. The G40SA50 sample shows the same precipitated crystal phases of β-and γ-AgI as G10SA70 (Fig. 2a). Both glass-ceramic samples show two notable temperature changes at 147 °C and 120 °C in heating and cooling curves, respectively. The former temperature is ascribed to the β-/γ- to α-phase transition of AgI, and the latter is the α- to β-/γ-phase transition temperature. The suppression of the phase transition from α- to β-/γ-phase on cooling is similar to that observed in other AgI embedded systems.28 3.2. Ionic Transport Properties Figure 3a shows the Nyquist plots of impedance of the bulk samples. The impedance plot (25 °C) of the G40SA50 glass-ceramic sample, in which β- and γ-AgI 7



crystal phases are embedded (similar to G10SA70), exhibits a semicircle and a spike in the low-frequency region, suggesting that this sample behaves as a typical ionic conductor. Previous studies on Ag-ion containing chalcogenide glasses clearly indicated that conductivity in these samples originates predominantly from fast Ag-ion conduction.3, 29, 30 The intercept of the depressed semicircle with the x axis yields a conductivity σ=R−1(L/A), where A and L are the area of the electrodes and the distance between them, respectively. The impedance plot of the G40SA50 sample recorded at 75 °C shows a diminishing semicircle, indicating that resistance (R) decreases with increasing temperature. By contrast, the plot of G2.5SA70 recorded at 25 °C showed only one spike. (a)

1800

(b)

40

G2.5SA70

o

log[σ(s⋅cm )]

o

-1

@ 100 C 10

0

900

AgI

0

20

1200

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@ 25 C

30

1500

Z'' / ohm

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0

20

40

60

100

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o

G40SA50 @ 25 C

600

G40SA50

-1

G2.5SA70

-2

G33SA45

-3 G30SA40

-4 -5

300 o

G40SA50 @ 75 C

-6

0 0

300 600 900 1200 1500 1800

1.8

2.1

Z' / ohm

2.4

2.7

3.0

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3.6

-1

(1000/T) / K

Figure 3. (a) Nyquist plot of impedance of 2.5GeS2–27.5Sb2S3–70AgI (G2.5SA70) at 25 °C, and 40GeS2–10Sb2S3–50AgI (G40SA50) at 25 °C and 75 °C. The inset shows a zoom plot of impedance of G2.5SA70 at 25 °C and 100 °C. (b) Temperature dependence of the conductivities of 30GeS2–30Sb2S3–40AgI (G30SA40), 33GeS2– 22Sb2S3–45AgI (G33SA45), G2.5SA70 glasses, and G40SA50 glass-ceramic sample for a thermal cycle. The conductivity data for AgI polycrystals are also included for comparison.

Figure 3b shows the temperature dependences of the conductivities of GeS2–Sb2S3– AgI glasses, glass-ceramic sample, and AgI polycrystals.7 The electrical conductivity 8


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of AgI polycrystals shows a large leap from 10−4 S/cm to 1 S/cm at the threshold temperature of 147 °C. This result is due to the β-/γ- to α-phase transition of AgI. A similar phenomenon was observed in the β-/γ-AgI embedded glass-ceramic samples with the composition outside of the glass-forming region (Fig. 1). For instance, G40SA50 presents a typical thermal cycle of the temperature dependence of conductivity as shown in Fig. 3b. During cooling, the conductivity of G40SA50 begins to decrease at 120 °C, which is in agreement with the sharp exothermic peak observed in the DSC curve (Fig. 2b). The conductivities of GeS2–Sb2S3–AgI glassy samples under investigation, as shown in Fig. 3b, followed Arrhenius behavior, which is attributed to the thermally activated hopping of Ag+ ions in them. The RT conductivity of the glasses increases noticeably with silver concentration from 6.31×10−5 S/cm to 9.18×10−3 S/cm. G2.5SA70 glass shows a maximum RT conductivity of 9.18×10−3 S/cm and a low activation energy (Ea) of 0.07 eV. This conductivity value reaches the limit value of conductivity (~10−2 S/cm) in several kinds of AgI-containing glasses regardless of the species of the glass network formers.31, 32 The notable ionic transport properties of the G2.5SA70 glass are entirely reproducible in thermal cycles below Tg (135 °C). The conductivity of G2.5SA70 glass is compared with the conductivities of other Ag-ion conducting glassy electrolytes (Fig. 4a). G2.5SA70 glass exhibits higher RT conductivity than other Ag-containing chalcogenide glasses3, 31, 33, 34 and several oxide glasses.16,

34-36

Melt-quenched 70AgI–30Ag2SeO4 glass has a comparable RT

conductivity.35 Glassy 60AgI–40Ag2MoO4 exhibits high conductivity of 10−1 S/cm at 9



RT, and its Tg is lower than 50 °C.36, 37 Although the conductivity of the G2.5SA70 glassy electrolyte is one order of magnitude lower than that of 60AgI–40Ag2MoO4 glass, this sulfide glass results in a broad operation temperature range which is suitable for practical battery applications. (a) G2.5SA70

0

60AgI-40Ag2MoO4 45GeS2-55Ag2S 85Ag2S-15Sb2S3

-1

log[σ(s⋅cm )]

-2 40Ag2Se

-4

70AgI-30Ag2SeO4

-10Ga2Se3 -50GeSe2

-6

50Ag2S-50AgPO3 20GeS2-40Ga2S3 -40AgI

-8 10AgI-27Ag2O-31.5SeO2-31.5MoO3 30Ag2O-35SeO2-35TeO2

-10 2

30AgI-70AgPO3

3

4

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7

-1

1000/T (K ) (b) 0.6

Activation energy, Ea / eV

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0.5 0.42

Ox ide

0.4

es lfid Su

s

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0.3

0.27 0.23

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O4

S5

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O3

0.15 0.07

O2

S4 S3

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S2

O1 S0

S1

0.0

Figure 4. (a) Thermal evolution and (b) activation energies of the ionic conductivity of new 2.5GeS2–27.5Sb2S3–70AgI (G2.5SA70) glass (S0), together with those of other silver glassy solid electrolytes: 60AgI–40Ag2MoO4 (O1),36 70AgI–30Ag2SeO4 (O2),35 85Ag2S–15Sb2S3 (S1),34 50Ag2S–50AgPO3 (O3),38 45GeS2–55Ag2S (S4),31 10AgI–27Ag2O–31.5SeO2–31.5MoO3 (O4),16 40Ag2Se–10Ga2Se3–50GeSe2 (S3),3 30Ag2O–35SeO2–35TeO2,39 30AgI–70AgPO3,40 3Sb2S3–57Ag2S–40AgI (S2),41 and 20GeS2–40Ga2S3–40AgI (S5).33

A comparison of activation energies of various sulfide and oxide electrolytes is given in Fig. 4b. To the best of our knowledge, the G2.5SA70 glass not only exhibits the highest RT conductivity of Ag+ ion reported for chalcogenide glasses but also the 10


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lowest activation energy for all Ag-containing glassy electrolytes. The activation energy of 0.07 eV is comparable with that of bulk α-AgI (~0.05 eV). This low activation energy may originate from the local network structure of G2.5SA70 glass. Analysis of the structure of GeS2–Sb2S3–AgI glasses is necessary to shed light on the correlation between local network structure and Ag-ion conduction in the new superionic conductor with notable ionic transport properties. 3.3. Possible Diffusion Pathway During ion diffusion, mobile ions require sufficiently large energy to open up pathways in the structure and to jump/hop from one site to another. According to the Anderson–Stuart model,42 this energy is determined by Ea = Eb + Es, where Eb (the binding energy) is the average energy a cation requires to leave its site; Es (the strain energy) is the mean kinetic energy a cation needs to open a “doorway” in the structure to pass through. Previous studies on the structure–conductivity correlation in AgI ion-conducting glasses43-45 suggest that the expansion of glass network structure induced by AgI dopant lowers the strain energy part Es of the activation energy; moreover, the formation of pathways decreases Eb. Thus, the exceptionally low activation energy of Ag-ion diffusion in this work is determined by large pathway volume and special pathways, in which the Ag+ ions may coordinate both sulfur and iodine in the network structure of GeS2–Sb2S3–AgI glasses. For further understanding the structural origin for activating fast Ag-ion conduction with low migration barriers, the glass network structure of GeS2–Sb2S3–AgI glasses with high AgI content is studied by Raman spectra. Figure 5 presents the Raman 11



spectra of three GeS2–Sb2S3–AgI glasses of G2.5SA70, G20SA60, and G15SA60 together with those of GeS2–Sb2S3 glasses and crystallites of Sb2S3, SbSI, and SbI3 reported previously.46-48 We divided these spectra into three regions from high to low frequency as shown in Fig. 5. The first region ranging from 350 cm−1 to 450 cm−1 includes two Raman bands located at 360 and 419 cm−1, respectively. Clearly, the intensity of these two Raman bands is directly related to GeS2 content in these glasses. According to the detailed Raman studies on GeS2–Sb2S348 and GeS2–SbSI,49, 50 these Raman bands at 360 and 419 cm−1 originated from the vibration of [GeS4−xIx] structural units.

2

Raman Intensity / a.u.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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3

1 50GeS2-50Sb2S3 G20SA60 G15SA60 G2.5SA70 10GeS2-90Sb2S3 Sb2S3 360

419

SbSI 238 280 107 138 162

100

SbI3

200

319 308

300

400

500

-1

Raman shift / cm

Figure 5. Raman spectra of 2.5GeS2–27.5Sb2S3–70AgI (G2.5SA70), 20GeS2– 20Sb2S3–60AgI (G20SA60), 15GeS2–25Sb2S3–60AgI (G15SA60), 50GeS2– 50Sb2S3,48 10GeS2–90Sb2S3,48 and crystallites of Sb2S3,48 SbSI,46 and SbI3.47

The second region ranging from 200 to 350 cm−1 shows a dominated Raman band. 12


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As shown in Fig. 5, this band can be fitted by the characteristic Raman peaks of Sb2S3 and SbSI crystallites,46,

48

which are centered at 238, 280, 308, and 319 cm−1.

Furthermore, in the third region ranging from 50 to 200 cm−1, three Raman peaks centered at 107, 138, and 162 cm−1 for the GeS2-Sb2S3-AgI glasses can be explained by those of SbI3 and SbSI.46,

47

Therefore, the networks of the GeS2–Sb2S3–AgI

glasses with high AgI content are constructed mainly from [SbS3−xIx] pyramids, as well as a few [GeS4−xIx] tetrahedra, and mobile Ag+ ions are randomly located between those structural units.

Figure 6. Structure of SbSI crystal looking down the c axis at ab plane (a) and viewing along b axis (b); (c) Schematic of the typical local structure of GeS2–Sb2S3– AgI glasses containing high AgI content (such as 2.5GeS2–27.5Sb2S3–70AgI).

Figures 6a and 6b display the crystal structure of SbSI, which is constructed in the orthorhombic space group Pnma according to the crystallographic data of standard JCPDS file (No. 01-074-1195). SbSI presents a ribbon stack framework, which is composed of chains joined together by weak van der Waals force. Each chain is mainly formed from distorted edge sharing pseudo-octahedral of two Sb–I bonds and 13



three Sb–S bonds along with the lone pair electron of Sb.51 Reasonably, the chains in SbSI ribbon stack framework are inherited for GeS2–Sb2S3–AgI glasses with high AgI content when the mobile Ag+ ions and a small amount of GeS2 are incorporated to disorder the network (Fig. 6c). In the disordered glassy network structure, chain fragments composed of [SbS3−xIx] pyramids are connected by [GeS4−xIx] tetrahedra, and mobile Ag ions randomly disperse around I− anions. The ionic transport channel of Ag+ ions here is similar to that of mobile Li+ ions in the superionic conductor of Li10GeP2S12.52 In Li10GeP2S12 crystal, a typical concerted migration involves four Li ions occupying Li1 and Li3 sites hopping simultaneously along the c channel into their nearest-neighbor Li3 and Li1 sites, respectively. The migration barrier of this concerted migration were calculated as 0.2 eV, 52 which is the lowest one in the Li-ion conducting solid electrolytes. Thus, it is reasonable to propose that, as shown in Fig. 6c, Ag+ ions at Ag1 and/or Ag2 sites (even more) would hop simultaneously to their nearest-neighbor sites, resulting in concerted hopping of multiple Ag+ ions along the diffusion channel composed of the ribbon-like chains of [SbS3−xIx]n. This infinite migration channels between the fragments facilitate the fast Ag-ion conduction with low migration barrier, resulting in the high RT conductivity of 9.18×10−3 S/cm and the exceptionally low activation energy of ~0.07 eV in G2.5SA70 glass.

4. Conclusions

A series of chalcogenide glasses and glass-ceramic samples in GeS2–Sb2S3–AgI

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system are prepared, and its glass formation regions is expanded toward notably high AgI content (70 mol%). Ag-ion conduction in the as-prepared samples is studied by ac impedance measurement together with the thermal and structural characterization of DSC, XRD, and Raman spectra. A notable superionic transport behavior is observed in the homogeneous GeS2–Sb2S3–AgI glasses with good thermal stability (high Tg). The highest RT Ag-ion conductivity of 9.18×10−3 S/cm reported in chalcogenide glasses is achieved in 2.5GeS2–27.5Sb2S3–70AgI glass. The glassy sample presents the lowest activation energy (0.07 eV) for all Ag-containing glassy electrolytes. This activation energy is comparable with that of bulk α-AgI (~0.05 eV). Possible diffusion pathway, which is responsible for the exceptionally low activation energy, is established based on the ribbon stack framework of SbSI. In the disordered local network structure of GeS2–Sb2S3–AgI glasses, chain fragments composed of [SbS3−xIx] pyramids are connected by [GeS4−xIx] tetrahedra, and mobile Ag+ ions are randomly located around I− anions. The infinite ionic transport channels between fragments allow for long-range transport of Ag+, resulting in fast Ag-ion conduction and its exceptionally low activation energy. This finding provides a new glassy electrolyte for solid-state batteries operating in a broad temperature range especially below room temperature, as well as new opportunities in developing novel fast ionic conductors based on the disordered structure composed of [SbS3−xIx]n chains.

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Acknowledgements

This work was partially supported by National Natural Science Foundation of China (Grant Nos. 61775110 and 61435009), and The National Key Research and Development Program of China (Nos. 2016YFB0303802 and 2016YFB0303803). It was also sponsored by K. C. Wong Magna Fund in Ningbo University.

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