Synthesis of Orthorhombic Perovskite-Type ZnSnO3 Single-Crystal

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Synthesis of orthorhombic perovskite-type ZnSnO3 singlecrystal nanoplates and their application in energy harvesting Runjiang Guo, Yiping Guo, Huanan Duan, Hua Li, and Hezhou Liu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b16629 • Publication Date (Web): 17 Feb 2017 Downloaded from http://pubs.acs.org on February 19, 2017

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ACS Applied Materials & Interfaces

Synthesis of Orthorhombic Perovskite-Type ZnSnO3 Single-Crystal Nanoplates and Their Application in Energy Harvesting Runjiang Guo, Yiping Guo,* Huanan Duan, Hua Li, Hezhou Liu State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai 200240, China *

Email address: [email protected]

Tel.: 86-21-54738972, Fax: 86-21-34202749 ABSTRACT In recent years, lead-free piezoelectric nanogenerators have attracted much attention because of their great potential for harvesting energy from the environment. Here, we report the first synthesis of two-dimensional (2D) single-crystal ZnSnO3 hexagon nanoplates and the fabrication of ZnSnO3 nanoplate-based nanogenerators. The orthorhombic perovskite-structured ZnSnO3 nanoplates with (111) facets of the exposed plate surface are successfully synthesized via a one-step hydrothermal reaction. Piezoelectric nanogenerators are then fabricated using the as-synthesized single-crystal ZnSnO3 nanoplates and poly(dimethylsiloxane) (PDMS). A d33 value as high as 49 pC/N for the ZnSnO3@PDMS composite was obtained without any electrical poling process, which demonstrates that the single-crystal ZnSnO3 nanoplates have a single-domain structure. To the best of our knowledge, this d33 value is also the highest among lead-free piezoelectric composites. A bending strain can induce the piezoelectric nanogenerator (PENG) to generate a large, stable and sustainable output open circuit voltage of 20 V and a short circuit current of 0.6 µA, which are higher than many other PENGs. The output signals are sufficient to light a single LED, which shows the material’s great potential for scavenging mechanical energy from moving entities, such as road vehicles, railway vehicles and humans. KEYWORDS: energy harvesting, piezoelectric nanogenerator (PENG), lead-free ZnSnO3, two-dimensional (2D) material, flexible composite 1

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1. INTRODUCTION Over recent decades, energy harvesting from the environment to resolve environmental problems and energy deficiencies has received widespread attention. Since Wang and his co-worker fabricated the first ZnO nanowire-based piezoelectric nanogenerator (PENG) in 2006, energy harvesting has been a popular research field.1-5 PENG can transform mechanical strains, such as human motion, mechanical vibrations, stream flow and acoustic noise, into electric energy via the piezoelectric effect. The nanogenerators that have been reported are mostly based on three-dimensional (3D) or one-dimensional (1D) materials.1-5 In the past few years, the emergence of two-dimensional (2D) nanostructures, such as nanosheets, nanoplates and nanowalls, has attracted much attention.6-8 Flexible composite nanogenerators based on 2D materials tend to have better piezoelectric performance because of the unidirectional orientation of the exposed plate surface. And flexible composite nanogenerators based on 2D materials also tend to have a uniform performance under different stress conditions.7,8 Therefore, it is useful to synthesize 2D materials and fabricate their corresponding nanogenerators. Various kinds of piezoelectric materials have been used to fabricate nanogenerators, including ZnO, Pb(Zr,Ti)O3 (PZT), BaTiO3 (BTO), (K, Na)NbO3 (KNN), ZnSnO3, GaN, MoS2, etc.1,9-17 Among these, PZT has the highest piezoelectric constant, but the conductivity of PZT is very low, which is not conducive to the improvement of output performance. Moreover, high lead content of PZT is environmentally harmful.18 Synthesizing low-dimensional, single-crystal, lead-free piezoelectric nanomaterials is a good way to solve these problems. However, most piezoelectric nanomaterials have polycrystalline and multi-domain structures, and thus a poling process with the application of high voltage is necessary to obtain a good piezoelectric response. Among the available, appropriate, lead-free piezoelectric nanomaterials, ZnSnO3, as a multifunctional material, has attracted considerable interest in recent years and has great potential in applications in many fields, such as gas/humidity sensors, Li-ion batteries and photocatalysis.19-23 Because of its non-centrosymmetric structure, high polarization (Pr = 59 µC/cm2).24 semiconductor nature and self-polarization behavior, ZnSnO3 has also been widely used in energy harvesting recently.14,15 ZnSnO3 has two crystal structures, the perovskite structure and the ilmenite (LN-type) structure.24-27 Since ZnSnO3 is a metastable material, which is only 2


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thermally stable below 750 ℃, it is easily decomposed into Zn2SnO4 and SnO2 above 750 ℃.28,29 Therefore, it is hard to synthesize pure ZnSnO3 via conventional solid state reaction. At present, perovskite- and ilmenite-type ZnSnO3 are usually synthesized via hydrothermal reaction and carbon thermal reaction, respectively. ZnSnO3 with an ilmenite structure should have a lower piezoelectric constant than that of ZnSnO3 with a perovskite structure, and the synthetic process is more complicated. Perovskite ZnSnO3 nanocubes synthesized via hydrothermal reaction without any calcination, as previously reported, are thought to be ZnSn(OH)6,14,15,30 which is supported by other reports.20,31,32 2D mesocrystals ZnSnO3 with sheet-like structures have ever been synthesized by a hydrothermal reaction and subsequent calcination process. And it is reported that the ZnSnO3 nanoplates as an anode material for Li-ion batteries exhibited good cycle abilities and rate performance.21 However, from the XRD and SAED patterns, we may infer that the crystallinity of the ZnSnO3 nanoplates in that work is poor. Thus, further study of the facile synthesis of perovskite-structured ZnSnO3 is highly desirable. Especially, it is of significance to develop a feasible method to synthesize 2D ZnSnO3 materials with both high crystallinity and selected facets for piezoelectric application. In this paper, the synthesis of 2D orthorhombic perovskite ZnSnO3 hexagon nanoplates with a (111) orientation of the exposed surface of the plates is first reported via a one-step hydrothermal reaction. The whole process is environment friendly and does not use any toxic elements or alkali reagents (NaOH). A sandwich-like PENG based on the orthorhombic ZnSnO3 nanoplates and PDMS is then fabricated. The d33 value of the ZnSnO3@PDMS composite can reach up to 49 pC/N. The PENG exhibits a large open circuit voltage of 20 V and short circuit current of 0.6 µA under periodic bending stress. The output signals are sufficient to power a single LED, which demonstrates the potential applications of this material for use in higher power nanogenerators, high sensitivity nanosensors and large strain nanoactuators. Mechanisms of the formation of the orthorhombic ZnSnO3 nanoplates and the generation of the piezoelectric output are also discussed.

2. EXPERIMENTAL SECTION 2.1. Materials Synthesis and Characterization The ZnSnO3 nanoplates were synthesized via the hydrothermal method. In a typical synthetic process, 0.569 g of Na2SnO3·4H2O and 0.439 g of ZnAc2·2H2O are dissolved in 20 mL of deionized water respectively. Then, the Na2SnO3 solution is added dropwise to the ZnAc2 solution 3



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under magnetic stirring. The white suspension is then transferred into a Teflon-lined stainless-steel autoclave and maintained at 260 ℃ for 24 h. After cooling, centrifuging and drying, a milk-white ZnSnO3 powder is obtained. To investigate the growth process, intermediate products were collected at different reaction temperatures of 160 ℃, 170 ℃, 180 ℃, 210 ℃, and 240 ℃ after 24 h and different reaction times of 2 h, 4 h, 8 h and 12 h at 260 ℃. The morphologies and microstructures of the ZnSnO3 nanoplates were characterized by scanning electron microscopy (SEM, FEI Sirion 200), transmission electron microscopy (TEM, JEM 2100F) and high-resolution transmission electron microscopy (HR-TEM, JEM 2100F) with an accelerating voltage of 200 kV. The crystal structures of the products were determined by X-ray diffraction (XRD, Rigaku D/MAX255ovl/84) with Cu Kα radiation at a scan speed of 5°/min. (35 kV, 200 mA) and thermal analysis (TG, Pyris 1 TGA). The piezoelectric response was evaluated using piezoresponse force microscopy (PFM, mfp-3d Asylum Research) with a driving voltage of 4 V and a d33 meter (ZJ-3AN). 2.2. Fabrication and Measurements of PENG

Figure 1. Schematics of (a) the fabrication process of ZnSnO3@PDMS PENG and (b) the structure of ZnSnO3@PDMS PENG.

First, PDMS, a curing agent and ethyl acetate were mixed together at a weight ratio of 10/1/2, in which ethyl acetate acts as a diluent to make the mixture less vicious. Then, the as-synthesized ZnSnO3 powder was dispersed into the PDMS mixture at different concentrations of 5, 10, 15, 20, 4


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25 and 30 wt%. After agitating for 8 h, the ZnSnO3@PDMS mixture was poured onto a flexible ITO film, which acts as the bottom electrode. After that, the composite was put in a vacuum oven for 30 min to eliminate air bubbles and then cured at 120 ℃ for 3 h. After curing, another flexible ITO film was attached to the surface of the ZnSnO3@PDMS composite film as the upper electrode. At last, this nanogenerator was encapsulated by PDMS to make the whole device flexible and durable. The whole fabrication process and the structure of ZnSnO3@PDMS PENG are illustrated in Figure 1a,b respectively. The thickness and effective size of all of the as-fabricated ZnSnO3@PDMS PENGs are approximately 300 µm and 1 cm × 1 cm respectively. Output signals of the ZnSnO3@PDMS PENGs are generated by pressing (from a linear motor, the frequency is 0.25 Hz) or bending (the frequency by the human finger bending or releasing is about 2 Hz) and collected by a digital source meter (Keithley 2400). A single LED is utilized to test the output signals from the ZnSnO3@PDMS PENGs.

3. RESULTS AND DISCUSSION The phase information and the crystal structure of the as-synthesized products were delineated using X-ray diffraction (XRD) analysis and thermogravimetric (TG) analysis. Figure 2a-c shows the XRD patterns of the powders synthesized at 160 ℃, 180 ℃ and 260 ℃ respectively. All of the diffraction peaks in Figure 2a are assigned to the standard ZnSn(OH)6 phase (JCPDS card no.73-2384), which means that when the hydrothermal temperature is below 160 ℃, the as-produced powder is ZnSn(OH)6 rather than ZnSnO3. (see in the supporting information “Phase investigation on zinc–tin composite synthesized at 160 ℃”) The main diffraction peaks in Figure 2b belong to the orthorhombic perovskite ZnSnO3 phase26,33-35 but there are also some residual peaks belonging to the ZnSn(OH)6 phase (labelled by asterisk), indicating a partial transformation of the ZnSn(OH)6 phase into the ZnSnO3 phase at the hydrothermal temperature of 180 ℃. When the hydrothermal temperature reaches up to 260 ℃, all the diffraction peaks in Figure 2c ascribed to the orthorhombic perovskite ZnSnO3 phase, indicating that ZnSn(OH)6 is no longer present. In addition, the diffraction peaks in Figure 2c are stronger than those in Figure 2b, which suggests that we can obtain pure orthorhombic perovskite ZnSnO3 with high crystallinity by elevating the hydrothermal temperature. The XRD results are also consistence with those of TG analysis. As shown in Figure 3, for 5



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ZnSn(OH)6, there is a rapid weight loss of approximately 19% between 180 ℃ and 260 ℃, which is due to the following reaction: 180℃ ZnSn(OH )6 ≥ → ZnSnO 3 + 3H 2O (1)

The calculated weight loss according to this equation should be 21%, which is very close to the experimental result, while there is nearly no weight loss of ZnSnO3 over the whole heating process.

Figure 2. (a) XRD pattern of ZnSn(OH)6 synthesized at 160 ℃. (b) XRD pattern of ZnSnO3 synthesized at 180 ℃. (c) XRD pattern of ZnSnO3 synthesized at 260 ℃.

6


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Figure 3. TG curves of as-prepared ZnSn(OH)6 and ZnSnO3 at a heating rate of 10 ℃/min under N2 atmosphere. The morphology of the as-synthesized orthorhombic ZnSnO3 was characterized by SEM, TEM and HR-TEM. From the typical SEM and TEM images of the as-synthesized ZnSnO3 samples (Figure 4a-c), hexagon plate-like ZnSnO3 particles with an average thickness of 20 nm are clearly observed. The HR-TEM image of the surface of an individual nanoplate and its corresponding selected-area electron diffraction (SAED) are shown in Figure 4d. The HR-TEM image of an individual nanoplate shows a lattice spacing of 0.26 nm, which corresponds to the (111) lattice planes of orthorhombic ZnSnO3. From the SAED pattern in Figure 4d, there is only one set of diffraction spots for ZnSnO3, which indicates that the single-crystal hexagon ZnSnO3 nanoplates were successfully synthesized via the one-pot hydrothermal reaction. The TEM image and the SAED pattern of ZnSnO3 synthesized at 180 ℃ are also shown in Figure S1. There are no hexagon ZnSnO3 nanoplates observed in the TEM image. From the unaligned fringes in the HRTEM image and diffraction rings in the SAED pattern, it is evident that ZnSnO3 synthesized at 180 ℃ should be polycrystalline.

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(a)

(b)

(c)

(d) 0.26nm (111)

Figure 4. Typical (a) SEM, (b)-(c) TEM and (d) HRTEM images and SAED pattern inset of ZnSnO3 synthesized at 260 ℃. To investigate the influence of temperature on the morphology of the ZnSnO3 nanoparticles, a series of temperature dependence experiments were conducted, as shown in Figure 5a-e. When the hydrothermal reaction is conducted at 160 ℃, uniform cubic-like ZnSn(OH)6 with a width of 250 nm is obtained. When hydrothermally reacted at 170 ℃, the cubic-like ZnSn(OH)6 decomposes into ZnSnO3 in an irregular shape. As the temperature increases to 210 ℃, irregular nanoflakes are formed. When the hydrothermal temperature reaches up to 260 ℃, uniform single-crystalline hexagon plate-like ZnSnO3 is finally formed.

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(a)

(b)

(c)

(d)

(e)

Figure 5. Typical SEM images of ZnSnO3 synthesized at (a) 160 ℃, (b) 170 ℃, (c) 180 ℃, (d) 210 ℃ and (e) 240 ℃ under hydrothermal conditions. To explain the formation mechanism of the orthorhombic ZnSnO3 nanoplates, a series of time dependence experiments were carried out, as shown in Figure 6a-d. When the hydrothermal reaction time reaches 2 h, the ZnSn(OH)6 cubes begin to dissolve and a large quantity of cleavage fragments on the surfaces of these cubic shapes can be clearly observed. With the hydrothermal reaction time extends to 4 h, the cubic structures begin to evolve into nanoplates accompanied by 9



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many irregular nanoparticles. After 8 h of reaction, an increasing number of small particles aggregate into nanoplates. As the hydrothermal reaction time is prolonged to 12 h, the small particles completely disappear, and they assemble into hexagon nanoplates. The dissolution and recrystallization mechanism has been proposed for the formation of many nanostructured materials, which should also be suitable for this hydrothermal reaction.21,33,36-38 In this process, Zn(OH)42- and H2SnO3 are produced in each solution first. After mixing the reactants, Zn(OH)42and H2SnO3 form ZnSn(OH)6 nuclei, and then these nuclei grow into cubic-like crystals. With an increase in temperature and pressure, the metastable cubic-like ZnSn(OH)6 nanoparticles gradually dissolve into solution and form massive irregular-shaped nanoparticles that have many high-energy sites for growth of the nanocrystals. Then, these nanoparticles aggregate spontaneously into flake-like units to reduce the surface energy. In the subsequent stage, these flake units reassemble into larger hexagon nanoplates. A schematic illustration of the formation mechanism of the hexagon ZnSnO3 nanoplates is shown in Figure 6e. The whole formation process can be summarized as follows.

SnO32− + 2 H 2O ← → H 2 SnO3 + 2OH −

(2)

Zn 2+ + 4 H 2O ← → Zn(OH ) 24− + 4 H +

(3)

2− 4

+

H 2 SnO3 + Zn(OH ) + 2 H  → ZnSn(OH ) 6 ↓ + H 2O ∆

ZnSn(OH ) 6  → ZnSnO3 + 3H 2O

(4) (5)

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(a)

(b)

(c)

(d)

(e)

Figure 6. SEM images of the products obtained after hydrothermal reaction times of (a) 2 h, (b) 4 h, (c) 8 h and (d) 12 h. (e) Schematic illustration of the formation mechanism of ZnSnO3 nanoplates.

ZnSnO3 has excellent piezoelectricity, but it is fragile and lossy. By contrast, PDMS is flexible and durable but has no piezoelectricity. Therefore, a ZnSnO3@PDMS composite PENG 11



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that combines the advantages of high piezoelectricity and excellent flexibility is a good candidate for energy harvesting.39 A schematic representation of the fabricated sandwich-like ZnSnO3@PDMS PENG is shown in Figure 1b, which mainly consists of three layers. The ZnSnO3 nanoplates are homogeneously dispersed into PDMS and then sandwiched between two flexible indiums tin oxide (ITO) electrodes.

Figure 7. Variation in the output voltage of PENGs with different ZnSnO3 concentrations.

A series PENGs were fabricated with different ZnSnO3 weight ratios (0-30 wt% ZnSnO3). To measure the piezoelectric output signals, a periodic bending stress was applied to the PENGs, and then the output signals were collected by a Keithley 2400 Source Measure Unit. As shown in Figure 7, when the weight ratio of ZnSnO3 is 0%, the output signals are approximately 200-300 mV, which should be the noise signal. The piezoelectric output voltage gradually increases to 18.5 V and then reaches a stable level at approximately 20 V with increasing ZnSnO3 content up to 20 wt% in the polymer matrix. However, the obtained output voltage from the PENGs with a higher weight ratio of ZnSnO3 (30 wt%) decreases. The low output voltage is mainly due to weak insulation of the composites, which could lead to electric breakdown when the concentration of 12


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ZnSnO3 is too high.14 In addition, excess ZnSnO3 cannot be well dispersed in the PDMS matrix, and thus the electric dipoles are unable to align in a large proportion.15 The optimum weight ratio of ZnSnO3 is approximately 20 wt%, which gains a maximum output voltage of 20 V. (a)

(b)

(c)

(d)

Figure 8. Piezoelectric (a) output voltage and (b) current generated from the ZnSnO3@PDMS PENG under bending strain. (c) Stability test of the ZnSnO3@PDMS PENG under vertical compressive force. (d) Output voltage generated under different bending strains. The maximum output open circuit voltage of 20 V and short circuit current of 0.6 µA are clearly shown in Figure 8a,b for the PENG with 20 wt% of ZnSnO3. The positive and negative signs of the voltage and current alternate with the stress state (Video S1). The resulting outputs from our ZnSnO3@PDMS PENG are higher than many previously reported hybrid PENGs based on other piezoelectric materials (Table 1). In addition, comparing with the PENGs based on ZnSnO3 nanocubes, the PENG based on ZnSnO3 nanoplates in our work has excellent output performances under bending strain (Table 1), which is more suitable for powering flexible and wearable electronic equipment. The output signals of the nanogenerator based on ZnSn(OH)6 (synthesized at 160 ℃) were also collected under the same testing conditions, and the output voltage of ZnSn(OH)6@PDMS PENG is only 2.5 V (Figure S2). The output performances of 13



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ZnSnO3 and ZnSn(OH)6 are consistent with the results of piezoresponse force microscopy (PFM) measurements, as shown in Figure S3. The piezoelectric response of the ZnSnO3 nanoplates (Figure S3a) is much larger than that of the ZnSn(OH)6 nanocubes (Figure S3b). The stability of the ZnSnO3@PDMS PENG was determined and is shown in Figure 8c. Even after hundreds of cycles of straining, though there are some fluctuations, the power-generation performance is quite stable, which means that the ZnSnO3@PDMS PENG can generate sustainable piezoelectric signals for a long time. The open circuit voltage increases with increasing bending level, as shown in Figure 8d. It is also noted that the ZnSnO3@PDMS PENG is so flexible and durable that it does not lose any efficiency even if the bending degree is very large. Table 1. Comparison of the Output Performances of Composite PENGs PENG

Output Voltage

Output Current

Reference

LiNbO3@PDMS

0.46 V

9 nA

39

NaNbO3@PDMS

3.5 V

70 nA

40

BaTiO3@PDMS

5.5 V

350 nA

41

ZnSnO3(nanobelt)

5.3 V

125 nA

12

ZnSnO3(nanocube)

20 V (Pressing)

900 nA (Pressing)

14

@PDMS

10 mV (Bending)

ZnSnO3(nanocube)

40 V (Pressing)

1500 nA (Pressing)

42

@PVA

1.5 V (Bending)

ZnSnO3(nanoplate)

16 V (Pressing)

600 nA (Bending)

This research

@PDMS

20 V (Bending)

@PDMS

To confirm that the output signals originate from the piezoelectric phenomenon, a polarity-switching test was performed. An opposite signal is observed when the ZnSnO3@PDMS PENG is connected in reverse (Figure 9a,b and Video S2). This demonstrates that the output signals are truly a result of the piezoelectric effect. The output signal created by bending and releasing of the device is able to power a single LED (Figure S4a and Video S3), which shows that the ZnSnO3@PDMS PENG has great potential for harvesting mechanical energy from human 14


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motion, mechanical vibration, stream flow and acoustic noise. Electric poling is necessary for most composite PENGs because the piezoelectric element has a multi-domain structure. However, as shown in Figure S4b, the d33 value of the ZnSnO3@PDMS composite can reach up to 49 pC/N even without any electrical poling process, which shows that we have successfully synthesized single-crystal ZnSnO3 nanoplates with a single-domain structure. Thus, without any electrical poling process, most of the electric domains will be in the same direction.10-13 In addition, to the best of our knowledge, this d33 value of the ZnSnO3@PDMS composite is the highest among lead-free piezoelectric composites. Although our results on

ZnSnO3 nanoplates show that they have excellent piezoelectric response, it is still quite elusive about the origin of the piezoelectric response at present. Orthorhombic type ZnSnO3 is supposed to have a space group Pnma.34 However, the centrosymmetric Pnma structure is non-polar. And it is also reported that the electronics can drive ferroelectricity in orthorhombic perovskite materials with space group Pbmn (Pnma) when the ion sizes are small.43-47 Therefore, it should be interesting to refine the crystal structure of ZnSnO3 so as to disclose the origin of the piezoelectric response. (a)

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(b)

Figure 9. Polarity-switching tests of the ZnSnO3@PDMS PENG: (a) forward switching and (b) reverse switching.

The working mechanism of the ZnSnO3@PDMS PENG is then shown in Figure S5. The whole PENG can be regarded as a capacitor, and the electron flow is driven back and forth through the external circuit.14 When no external force is applied to the device, most of the electric dipoles align in one direction. The positive and negative charges are bound at the top and bottom electrodes, respectively, and thus no piezoelectric output signal is generated. When the PENG suffers an external force, the domains rotate with the applied force, which leads to a change in the total polarization of the composite. In such a way, the bound charges will be discharged and then move to the opposite electrodes to screen the piezoelectric potential, which results in a piezoelectric potential between the top and bottom electrodes. When the applied mechanical force is released, the electric dipoles realign in one direction again; therefore, the charges transport back in a reverse direction and are bound again, which leads to an opposite electric signal.48 Thus, with periodic external force, alternating voltage and current are obtained. Because the single-crystal ZnSnO3 nanoplates have a particular orientation of the exposed plate surface, the electric dipoles are able to align in a large proportion, and thus nanogenerators based on 2D ZnSnO3 tend to have excellent performances.

4. CONCLUSIONS In conclusion, the orthorhombic perovskite 2D ZnSnO3 single-crystal nanoplates are first synthesized by a one-pot hydrothermal reaction. When the hydrothermal reaction is performed at 16


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260 ℃, single-crystal hexagon ZnSnO3 nanoplates with (111) facets of the exposed plate surfaces are obtained. Composite flexible PENGs based on ZnSnO3@PDMS are then fabricated. The d33 value of the ZnSnO3@PDMS composite can reach up to 49 pC/N without any electrical poling process, which demonstrates the self-polarization and single domain nature of the 2D hexagon ZnSnO3 nanoplates. The piezoelectric output voltage and current reach values of approximately 20 V and 0.6 µA, which are higher than many other nanogenerators and can drive a single LED. The working mechanism of the ZnSnO3@PDMS PENG is a stress-induced polarization rotation effect. The stability test shows that the PENG can constantly harvest mechanical energy from the living environment, which demonstrates that ZnSnO3 is a promising material for fabricating nanogenerators. SUPPORTING INFORMATION The Supporting Information is available free of charge on the ACS Publications website Video showing the powering up of the LED, the readings of Keithley 2400 (AVI) Typical TEM images and SAED pattern of the ZnSnO3 synthesized at 180 ℃, piezoelectric output voltage and current generated from the ZnSn(OH)6@PDMS based PENG under bending strain, PFM result of ZnSn(OH)6 and ZnSnO3 powder, the green LED driven successfully by hand bending and releasing, the d33 value of ZnSnO3@PDMS composite, the working mechanism of ZnSnO3@PDMS PENG, phase investigation on zinc–tin composite synthesized at 160 ℃ (PDF) ACKNOWLEDGMENTS This work is supported by the Natural Science Foundation of China (No. 51332009 and 11474199). The Instrumental Analysis Center of Shanghai Jiao Tong University is sincerely acknowledged for assisting with the relevant analyses.

REFERENCES (1) Wang, Z. L.; Song, J. Piezoelectric Nanogenerators Based on Zinc Oxide Nanowire Arrays. Science 2006, 312, 242-246. (2) Zhu, G.; Yang, R.; Wang, S.; Wang, Z. L. Flexible High-Output Nanogenerator Based on Lateral ZnO Nanowire Array. Nano Lett. 2010, 10, 3151-3155. (3) Chen, S.; Gao, C.; Tang, W.; Zhu, H.; Han, Y.; Jiang, Q.; Li, T.; Cao, X.; Wang, Z. Self-Powered Cleaning of Air Pollution by Wind Driven Triboelectric Nanogenerator. Nano 17



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

Energy 2015, 14, 217-225. (4) Kumar, B.; Kim, S. W. Energy Harvesting Based on Semiconducting Piezoelectric ZnO Nanostructures. Nano Energy 2012, 1, 342-355. (5) Wang, Z. L. Self-Powered Nanosensors and Nanosystems. Adv. Mater. 2012, 24, 280-285. (6) Wang, L.; Zhang, R.; Zhou, T.; Lou, Z.; Deng, J.; Zhang, T. P-Type Octahedral Cu2O Particles with Exposed {111} Facets and Superior CO Sensing Properties. Sensor Actuat. B-Chem. 2017, 239, 211-217 (7) Kim, K. H.; Kumar, B.; Lee, K. Y.; Park, H. K.; Lee, J. H.; Lee, H. H.; Jun, H.; Lee, D.; Kim, S. W. Piezoelectric Two-Dimensional Nanosheets/Anionic Layer Heterojunction for Efficient Direct Current Power Generation. Sci. Rep. 2013, 3, 2017. (8) Gupta, M. K.; Lee, J. H.; Lee, K. Y.; Kim, S. W. Two-Dimensional Vanadium-Doped ZnO Nanosheet-Based Flexible Direct Current Nanogenerator. ACS Nano 2013, 7, 8932-8939. (9) Chen, X.; Xu, S.; Yao, N.; Shi, Y. 1.6 V Nanogenerator for Mechanical Energy Harvesting Using PZT Nanofibers. Nano Lett. 2010, 10, 2133-2137. (10) Wang, Z.; Hu, J.; Suryavanshi, A. P.; Yum, K.; Yu, M. F. Voltage Generation from Individual BaTiO3 Nanowires under Periodic Tensile Mechanical Load. Nano Lett. 2007, 7, 2966-2969. (11) Gupta, M. K.; Kim, S. W.; Kumar, B. Flexible High-Performance Lead-Free Na0.47K0.47Li0.06NbO3 Microcube-Structure-Based Piezoelectric Energy Harvester. ACS Appl. Mater. Interfaces 2016, 8, 1766-1773. (12) Wu, J. M.; Xu, C.; Zhang, Y.; Yang, Y.; Zhou, Y.; Wang, Z. L. Flexible and Transparent Nanogenerators Based on a Composite of Lead Free ZnSnO3 Triangular Belts. Adv. Mater. 2012, 24, 6094-6099. (13) Wu, J. M.; Xu, C.; Zhang, Y.; Wang, Z. L. Lead-Free Nanogenerator Made from Single ZnSnO3 Microbelt. ACS Nano 2012, 6, 4335-4340. (14) Lee, K. Y.; Kim, D.; Lee, J. H.; Kim, T. Y.; Gupta, M. K.; Kim, S. W. Unidirectional High-Power Generation via Stress-Induced Dipole Alignment from ZnSnO3 Nanocubes/Polymer Hybrid Piezoelectric Nanogenerator. Adv. Funct. Mater. 2014, 24, 37-43. (15) Alam, M. M.; Ghosh, S. K.; Sultana, A.; Mandal, D. Lead-Free ZnSnO3/MWCNTs-Based Self-Poled Flexible Hybrid Nanogenerator for Piezoelectric Power Generation. Nanotechnology 18


Page 18 of 22

Page 19 of 22

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


2015, 26, 165403. (16) Lin, L.; Lai, C.-H.; Hu, Y.; Zhang, Y.; Wang, X.; Xu, C.; Snyder, R. L.; Chen, L.-J.; Wang, Z. L. High Output Nanogenerator Based on Assembly of GaN Nanowires. Nanotechnology 2011, 22, 475401. (17) Wu, W.; Wang, L.; Li, Y.; Zhang, F.; Lin, L.; Niu, S.; Daniel, C.; Zhang, X.; Hao, Y.; Heinz, T. F.; Hone, J.; Wang, Z. L. Piezoelectricity of Single-Atomic-Layer MoS2 for Energy Conversion and Piezotronics. Nature 2014, 514, 470-474. (18) Panda, P. K. Review: Environmental Friendly Lead-Free Piezoelectric Materials. J. Mater. Sci. 2009, 44, 5049-5062. (19) Wang, L.; Zhou, T.; Zhang, R.; Lou, Z.; Deng, J.; Zhang, T. Comparison of Toluene Sensing Performances of Zinc Stannate with Different Morphology-Based Gas Sensors. Sensor Actuat. B-Chem. 2016, 227, 448-455. (20) Zhou, T.; Zhang, T.; Zhang, R.; Deng, J.; Lou, Z.; Lu, G.; Wang, L. Highly Sensitive Sensing Platform Based on ZnSnO3 Hollow Cubes for Detection of Ethanol. Appl. Surf. Sci. 2017, 400, 262-268. (21) Chen, Y.; Qu, B.; Mei, L.; Lei, D.; Chen, L.; Li, Q.; Wang, T. Synthesis of ZnSnO3 Mesocrystals from Regular Cube-Like to Sheet-Like Structures and Their Comparative Electrochemical Properties in Li-Ion Batteries. J. Mater. Chem. 2012, 22, 25373-25379. (22) Lo, M.-K.; Lee, S.-Y.; Chang, K.-S. Study of ZnSnO3-Nanowire Piezophotocatalyst Using Two-Step Hydrothermal Synthesis. J. Phys. Chem. C 2015, 119, 5218-5224. (23) Fang, C.; Geng, B.; Liu, J.; Zhan, F. D-Fructose Molecule Template Route to Ultra-Thin ZnSnO3 Nanowire Architectures and Their Application as Efficient Photocatalyst. Chem. Commun. 2009, 2350-2352. (24) Inaguma, Y.; Yoshida, M.; Katsumata, T. A Polar Oxide ZnSnO3 with a LiNbO3-Type Structure. J. Am. Chem. Soc. 2008, 130, 6704-6705. (25) Xu, J.; Jia, X.; Lou, X.; Shen, J. One-Step Hydrothermal Synthesis and Gas Sensing Property of ZnSnO3 Microparticles. Solid-State Electronics 2006, 50, 504-507. (26) Wang, Y.; Gao, P.; Bao, D.; Wang, L.; Chen, Y.; Zhou, X.; Yang, P.; Sun, S.; Zhang, M. One Pot, Two Phases: Individual Orthorhombic and Face-Centered Cubic ZnSnO3 Obtained 19



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

Synchronously in One Solution. Inorg. Chem. 2014, 53, 12289-12296. (27) Kovacheva, D.; Petrov, K. Preparation of Crystalline ZnSnO3 from Li2SnO3 by Low-Temperature Ion Exchange. Solid State Ionics 1998, 109, 327-332. (28) Wang, Z.; Liu, J.; Wang, F.; Chen, S.; Luo, H.; Yu, X. Size-Controlled Synthesis of ZnSnO3 Cubic Crystallites at Low Temperatures and Their HCHO-Sensing Properties. J. Phys. Chem. C 2010, 114, 13577-13582. (29) Zhang, J.; Yao, K. L.; Liu, Z. L.; Gao, G. Y.; Sun, Z. Y.; Fan, S. W. First-Principles Study of the Ferroelectric and Nonlinear Optical Properties of the LiNbO3-Type ZnSnO3. Phys. Chem. Chem. Phys. 2010, 12, 9197-9204. (30) Wang, G.; Xi, Y.; Xuan, H.; Liu, R.; Chen, X.; Cheng, L. Hybrid Nanogenerators Based on Triboelectrification of a Dielectric Composite Made of Lead-Free ZnSnO3 Nanocubes. Nano Energy 2015, 18, 28-36. (31) Wang, D.; Wang, W.; Zhu, Z.; Sun, P.; Ma, J.; Lu, G. Phase Investigation on Zinc–Tin Composite Crystallites. RSC Adv. 2013, 3, 12084-12087. (32) Qin, Y.; Zhang, F.; Du, X.; Huang, G.; Liu, Y.; Wang, L. Controllable Synthesis of Cube-Like ZnSnO3@TiO2 Nanostructures as Lithium Ion Battery Anodes. J. Mater. Chem. A 2015, 3(6), 2985-2990. (33) Chen, Y.; Yu, L.; Li, Q.; Wu, Y.; Li, Q.; Wang, T. An Evolution from 3D Face-Centered-Cubic ZnSnO3 Nanocubes to 2D Orthorhombic ZnSnO3 Nanosheets with Excellent Gas Sensing Performance. Nanotechnology 2012, 23, 415501. (34) Tangcharoen, T.; Kongmark, C.; Pecharapa, W. Synchrotron X-ray Absorption Spectroscopy Study of the Local Atomic Structures and Cation Ordering in Perovskite-and Spinel-Type Zinc Stannate Synthesized by Co-Precipitation Method. J. Mol. Struct. 2015, 1102, 95-100. (35) Borhade, A.; Baste, Y. Study of Photocatalytic Asset of the ZnSnO3 Synthesized by Green Chemistry. Arab. J. Chem. http://dx.doi.org/10.1016/j.arabjc.2012.10.001. (36) Baruah, S.; Dutta, J. Zinc Stannate Nanostructures: Hydrothermal Synthesis. Sci. Technol. Adv. Mater. 2016, 12, 013004. (37) Wang, L.; Ng, W.; Jackman, J. A.; Cho, N. J. Graphene-Functionalized Natural Microcapsules: Modular Building Blocks for Ultrahigh Sensitivity Bioelectronic Platforms. Adv. Funct. Mater. 20


Page 20 of 22

Page 21 of 22

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


2016, 26, 2097-2103 (38) Lou, Z.; Chen, S.; Wang, L.; Jiang, K.; Shen, G. An Ultra-Sensitive and Rapid Response Speed Graphene Pressure Sensors for Electronic Skin and Health Monitoring. Nano Energy 2016, 23, 7-14. (39) Yun, B.; Park, Y.; Lee, M.; Lee, N.; Jo, W.; Lee, S.; Jung, J. Lead-Free LiNbO3 Nanowire-Based Nanocomposite for Piezoelectric Power Generation. Nanoscale Res. Lett. 2014, 9, 1-7. (40) Jung, J. H.; Lee, M.; Hong, J. I.; Ding, Y.; Chen, C. Y.; Chou, L. J.; Wang, Z. L. Lead-Free NaNbO3 Nanowires for a High Output Piezoelectric Nanogenerator. ACS Nano 2011, 5, 10041-10046. (41) Lin, Z. H.; Yang, Y.; Wu, J. M.; Liu, Y.; Zhang, F.; Wang, Z. L. BaTiO3 Nanotubes-Based Flexible and Transparent Nanogenerators. J. Phys. Chem. Lett. 2012, 3, 3599-3604. (42) Paria, S.; Karan, S. K.; Bera, R.; Das, A. K.; Maitra, A.; Khatua, B. B. A Facile Approach to Develop a Highly Stretchable PVC/ZnSnO3 Piezoelectric Nanogenerator with High Output Power Generation for Powering Portable Electronic Devices. Ind. Eng. Chem. Res. 2016, 55, 10671-10680. (43) Chen, H.; Yu, T.; Gao, P.; Bai, J.; Tao, J.; Tyson, T. A.; Wang, L.; Lalancette, R. Synthesis and Structure of Perovskite ScMnO3. Inorg. Chem. 2013, 52, 9692-9697. (44) Picozzi, S.; Yamauchi, K.; Sanyal, B.; Sergienko, I. A.; Dagotto, E. Dual Nature of Improper Ferroelectricity in a Magnetoelectric Multiferroic. Phys. Rev. Lett. 2007, 99, 227201. (45) Picozzi, S.; Yamauchi, K.; Bihlmayer, G.; Blugel, S. First-Principles Stabilization of an Unconventional Collinear Magnetic Ordering in Distorted Manganites. Phys. Rev. B 2006, 74, 094402. (46) Lorenz, B.; Wang, Y. Q.; Chu, C. W. Ferroelectricity in Perovskite HoMnO3 and YMnO3. Phys. Rev. B 2007, 76, 104405. (47) Sergienko, I. A.; Sen, C.; Dagotto, E. Ferroelectricity in the Magnetic E-Phase of Orthorhombic Perovskites. Phys. Rev. Lett. 2006, 97 (22), 227204. (48) Ren, X.; Fan, H.; Zhao, Y.; Liu, Z. Flexible Lead-Free BiFeO3/PDMS-Based Nanogenerator as Piezoelectric Energy Harvester. ACS Appl. Mater. Interfaces 2016, 8, 26190-26197. 21



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168x119mm (72 x 72 DPI)


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Synthesis of Orthorhombic Perovskite-Type ZnSnO3 Single-Crystal

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