Pressure-Induced Reversible Phase Transformation in Nanostructured

Jan 26, 2015 - Jian Zhang Jian Zhang , Hongyang Zhu , Xiaoxin Wu , Hang Cui , Dongmei Li , Junru Jiang , Chunxiao Gao , Qiushi Wang , Qiliang Cui...
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Pressure-Induced Reversible Phase Transformation in Nanostructured Bi2Te3 with Reduced Transition Pressure Guanjun Xiao,† Kai Wang,† Li Zhu,† Xiao Tan,† Yuancun Qiao,† Ke Yang,‡ Yanming Ma,† Bingbing Liu,† Weitao Zheng,† and Bo Zou*,† †

State Key Laboratory of Superhard Materials, College of Materials Science and Engineering, Jilin University, Changchun 130012, P. R. China ‡ Shanghai Synchrotron Radiation Facilities, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, P. R. China S Supporting Information *

ABSTRACT: High-pressure research on nanostructured materials has been of considerable interest owing to the quantum confinement effect and intrinsic defects in the nanocrystals. Here, we report a pressure-induced reversible structural phase transition in nanostructured Bi2Te3 hierarchical architectures (HAs) that were prepared via a facile solution-phase method. Therein, distinct phases I−IV by respectively adopting crystal structures of rhombohedral (I), monoclinic (II, III), and cubic (IV) were experimentally identified with increasing pressure up to 20.2 GPa in a diamond anvil cell (DAC). It is worthwhile to notice that nanostructured Bi2Te3 HAs ultimately evolved into a fascinating Bi−Te substitutional nonmetallic alloy at pressure even as low as 15.0 GPa, approximately 10 GPa lower than that of the corresponding bulk counterpart. The synergistic effect involving large volume collapse and the unique one-dimensional nanostructures with intrinsic antisite defects was proposed to be responsible for the reduction of transition pressure that is contrary to the general model for most nanomaterials. Our findings may pave a potential pathway for developing future multifunctional nanoalloys that are composed of nonmetallic elements.

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INTRODUCTION Alloys have been anticipated to be widely utilized in engineering and industry owing to their extraordinary properties, such as much stronger hardness and toughness, depressed electric and thermal conductivity, and lower melting point than each separated constituent alone.1,2 These unique characteristics of an alloy are able to render people manufacture the target material with desired properties for a given practical application. However, most alloys are composed of metal elements; thus, searching for other alternatives of new and enhanced functional alloys as well as their prepared strategy is of great interest and remains challenging. Applications of high pressure have proven to be a powerful tool in tailoring the material’s properties, especially since the development in the 1950s of the diamond anvil cell (DAC), which made it possible to generate pressures even above 100 GPa.3−6 Intriguingly, nanomaterials subjected to high-pressure conditions can greatly increase opportunities of exploring novel physical phenomena because of the quantum confinement effect and intrinsic defects yielded by the stark decrease in size.7−13 In this respect, Tolbert and Alivisatos, as pioneers in 1994, systematically investigated in situ high-pressure structural phase transition of monodispersed CdSe nanoparticles by applying DAC apparatus.14 Inspired by the size effect of © 2015 American Chemical Society

nanomaterials, Wang et al. have recently reported a critical sizedependent amorphization of nanoscale Y2O3 particles at high pressure.15 Meanwhile, Fan’s group further developed high pressure as a potential means for morphology regulation of noble metal nanocrystals.16−18 Our group has also made a progress in high-pressure nanomaterial studies over the different stabilities and phase transition routines for nanosized YPO4 particles as well as metastable phase binary MnS and ternary CuGaS2 nanocrystals.19−21 Consequently, high-pressure research on nanostructured materials has been of considerable significance not only for exploring the new structures and properties in materials but also for fundamental scientific contribution. Bi2Te3 has long been known as one of the best available thermoelectric materials with higher figure of merit (ZT) near room temperature.22 The latest discovery of three-dimensional topological insulators with a single Dirac cone on the surface in Bi2Te3 in particular made it much more fascinating.23,24 A very recent research by our group25 demonstrated that an unexpected room-temperature ferromagnetism in one-dimenReceived: December 17, 2014 Revised: January 20, 2015 Published: January 26, 2015 3843

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RESULTS AND DISCUSSION Nanostructured Bi2Te3 HAs were prepared through standard airless techniques in terms of the very recent report.25 The resulting products were first purified with toluene and methanol, and then a small amount of chloroform and an excess of acetone were added for repeatedly washing twice more. Figure 1a shows the overall FESEM image of the as-

sional (1D) nanostructured Bi2Te3 was identified as a result of intrinsic point defect with respect to the antisite Te site (BiTe2). The work provided new insights into the origin of magnetism and offered a promising opportunity to realize the quantum anomalous Hall effect.26,27 Despite the special interest in it, response of Bi2Te3 to high pressure has been yet rarely explored.28−32 Recently, Bi−Te subtutional nonmetallic alloy has been successfully achieved at pressure above 25 GPa,33,34 making high pressure a highly attractive route to synthesize novel alloys. Otherwise, best endeavoring to satisfy energy conservation remains a major concern to date, hence encouraging us to seek how to lower the applied pressure for the preparation of nonmetallic element alloys. Here, we present a pressure-induced reversible phase transition in nanostructured Bi2Te3 HAs that were prepared via a facile solution-phase route. Therein, phases I−IV by respectively adopting crystal structures of rhombohedral (I), monoclinic (II, III), and cubic (IV) were experimentally observed with increasing pressure up to 20.2 GPa in a DAC. It is worth noting that nanostructured Bi2Te3 HAs ultimately evolved into a fascinating Bi−Te substitutional nonmetallic alloy at pressure even as low as 15.0 GPa, approximately 10 GPa lower than that of the corresponding bulk counterpart. Large volume collapse and the unique 1D nanostructures with intrinsic antisite defects in the present case were proposed to give rise to the reduced transition pressure. Such findings may pave the feasible way for developing future nanoscale alloys that are composed of nonmetallic elements for a variety of highly desirable applications.

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Article

Figure 1. (a) Overall FESEM image of as-prepared nanostructured Bi2Te3 HAs. (b) TEM image of a typical caterpillar-like sample. The inset in (a) shows the high-magnification FESEM image with nanoplates intersection. Insets in (b) represent the corresponding SAED pattern (top) and HRTEM image (bottom).

synthesized nanostructured Bi2Te3 HAs. We can clearly see that the obtained samples possess caterpillar-like HAs with dimensions up to the micrometer scale, which was formed by the intersection of nanoplates with a thickness of about 20 nm (inset in Figure 1a). The unique layered crystal structure of Bi2Te3 bonded by van der Waals forces expedited the anisotropic growth of nanoplates. Eventually, the caterpillarlike Bi2Te3 HAs were formed driven by the aggregation and further ripening process. TEM image further reveals a typical caterpillar-like morphology with a HAs length of about 2 μm (Figure 1b). We have previously confirmed that the prepared caterpillar-like samples possessed a Bi-rich composition with substitutional defects of BiTe2. High-resolution TEM image represents apparent and continuous lattice fringes, which are indicative of the crystalline-like nature (bottom inset in Figure 1b). Moreover, interplanar spacing was measured to be about 3.24 Å, which corresponds to the (015) facet of the rhombohedral phase of Bi2Te3 with the space group D53d (R3m).37 The corresponding SAED pattern further confirms the rhombohedral crystal structure and polycrystalline nature (top inset in Figure 1b). As known to all, nanostructured materials would exhibit distinguished properties in contrast to their bulk counterparts and thus stimulating great enthusiasm to the cut-edge field of high-pressure nanomaterials research. In this regard, we devoted ourselves to investigating the pressure effect on the as-synthesized nanostructured Bi2Te3 HAs. As shown in Figure 2, in situ ADXRD patterns at selected pressures of the nanostructured Bi2Te3 HAs were performed with a wavelength of 0.6199 Å. Therein, silicon oil with the viscosity of 10 cst was utilized as PTM during the high-pressure experiments, which is comparable to a 4:1 mixture by volume of methanol and ethanol for maintaining hydrostaticity, as depicted in Figure S1. It turns out that all the diffraction peaks of the original rhombohedral phase simultaneously shift to greater angles with the increase in pressure, which corroborates the volume compression of nanostructured Bi2Te3 HAs with elevating

EXPERIMENTAL SECTION

High-Pressure Experiments. High-pressure experiments were conducted in a symmetric DAC furnished with a pair of 300 μm culet diamonds at room temperature. The prepared nanostructured Bi2Te3 HAs were enclosed into a ∼100 μm diameter hole of the T301 stainless-steel compressible gasket. Silicon oil with the viscosity of 10 cst was utilized as the pressure transmitting medium (PTM) which was purchased from the Dow Corning Corporation (South Saginaw Road, Midland, MI). Pressure determination was achieved by the fluorescence spectra of the ruby.35 In situ high-pressure angledispersive X-ray diffraction (ADXRD) patterns were recorded up to 20.2 GPa with a wavelength of 0.6199 Å at beamline 15U1, Shanghai Synchrotron Radiation Facility (SSRF), P. R. China. A focused beam size of about 4 × 7 μm2 was adopted for data collection. Partial ADXRD were conducted on 4W2 beamline at the High Pressure Station of the Beijing Synchrotron Radiation Facility (BSRF), P. R. China. The Bragg diffraction rings were collected by using the Mar-165 CCD detector with an average acquisition time of 10 s for each pressure and then were integrated on the basis of FIT2D program, yielding 1D intensity versus diffraction angle 2θ patterns.36 Characterization. The field-emission scanning electron microscopy (FESEM) measurements were carried out with a scanning electron microscope (JEOL, JSM-6700F) operated at an acceleration voltage of 8 kV. Selected area electron diffraction (SAED) pattern, transmission electron microscopy (TEM), and high-resolution TEM images were performed on a JEM-2200FS with an emission gun operating at 200 kV. 3844

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captured. Even at a lower pressure of 15.0 GPa, the bulk Bi2Te3 materials still remained a complex structure involving both phase III and IV, whereas for the present 1D nanostructured Bi2Te3 HAs, they have already experienced a complete conversion into the pure phase IV at the above-mentioned pressure. Since the complete phase transformation to phase IV for nanostructured Bi2Te3 HAs has achieved at 15 GPa, hence it would not have much effect on the observed results although pressure gradients became evident for silicon oil at above 15 GPa (Figure S2 and Table S1). A similar phenomenon was also reported by Jiang et al. in nanometer-sized γ-Fe2O3 particles, rutile-type TiO2 nanocrystals, and nanocrystalline CeO2, for which the phase transition pressures were much lower than that for the corresponding bulk materials.39−42 On the basis of thermodynamic theory concerning the Gibbs free energy change, it was believed that the ratio of volume collapses, the surface energy differences, and the internal energy differences would govern the change of transition pressure in nanocrystals,43 as shown in the subsequent equation: ΔG = ΔU − TΔS + PΔV, where G, U, S, and V represent the free energy, internal energy, entropy, and volume, respectively. It is reasonable to assume that ΔU and ΔS are analogous for the nanomaterials and the corresponding bulk counterparts. Thereby, the volume change ΔV is the dominant factor to determine the transformation of each other. The driving force ΔG is increased by the positive pressure−volume term of PΔV and thus lowering the energy barrier ΔG* in terms of the equation44 ΔG* = 16πσ3/[3(ΔGm − ΔGs)2ρ)]. Eventually, the larger volume change in the nanophase will lead to the nucleation * < ΔGbulk * . Therefore, the reduced transition barrier of ΔGnano pressures should be associated with a compression process overwhelmed by volume collapse. In addition, the nanoscale morphology has also proven to be a significant factor for regulating the structure and stability, accompanied by either early or delayed phase transitions.45−47 The large surface area of the 1D nanostructures and the correspondingly larger number of nucleation sites may be other factors that weaken the transformation barriers, thus contributing to the observed lower transition pressure. Otherwise, the intrinsic substitutional point defects regarding antisite BiTe2 in nanostructured Bi2Te3 HAs would further facilitate the bcc disordered occupancy of phase IV, although it does not disturb the sequence of phase transitions. Accordingly, all of these factors may interactively determine the depression of phase transition of nanostructured Bi2Te3 HAs that exhibited drastically different pressure responses than do bulk Bi2Te3 materials in this study. High-pressure crystal structures of the as-prepared nanostructured Bi2Te3 HAs are confirmed by the refinements of ADXRD patterns. As shown in Figure 3a, the refinements of the ADXRD pattern under ambient conditions match the experimental data points very well (Rwp = 1.20%, Rp = 0.77%). Therein, green vertical markers indicate the corresponding Bragg reflections. All of the diffraction peaks in the profile can be readily indexed and interpreted as rhombohedral phase Bi2Te3 (space group: R-3m) with cell constants of a = 4.39(5) Å and c = 30.19(8) Å. The sharp diffraction peaks corroborated the high crystallinity of the products. The great agreement (Rwp = 0.68%, Rp = 0.51%) toward simulations and ADXRD experiments at 11.9 GPa unraveled that high-pressure phases II adopted a monoclinic structure with space group of C2/m (Figure 3b). Excellent fittings (Rwp = 1.20%, Rp = 0.77%) of ADXRD pattern at 15.0 GPa between experimental and theoretical profiles enabled us to unambiguously determine

Figure 2. Representative in situ ADXRD patterns at selected pressures of the nanostructured Bi2Te3 HAs with the presence of silicon oil as PTM during the experiments performed at SSRF. Upon being completely quenched to the ambient conditions, ADXRD pattern retrieved its original rhombohedral structure again, despite the fact that strong iron peak deriving from T301 stainless-steel gasket still remained. The peaks marked with the arrow, asterisks, triangles, and rhombuses indicate the existence of phases I, II, III, and IV, respectively.

pressure. We can see that nanostructured Bi2Te3 HAs experienced three structural phase transformations in the experimental pressure range. The phase transition routines are in good accordance with the recent reports on the corresponding bulk Bi2Te3 and Sb2Te3 materials.33,34,38 The ambient peak of (015) crystal plane centered at 2θ of ∼11.02° remained up to 9.2 GPa and even existed as the pressure was further increased to 10.9 GPa, which is clearly marked with the arrow. However, new Bragg peaks denoted by open asterisks emerged as soon as the loading pressure reached 9.2 GPa, signifying the onset of initial structural phase transition to a monoclinic structured Bi2Te3 (phase II). This transformation was completed at 11.9 GPa, and the obtained phase II remained stable to 12.4 GPa. At the pressure of about 13.2 GPa, another monoclinic structure (phase III) appeared as a result of the disordered arrays of Bi and Te atoms in Bi2Te3 crystal structure. Note that phase III, marked with open triangles, can only stabilize in a narrow pressure range and coexist with both phase II and phase IV in the whole pressure range. Upon further compression to 15.0 GPa, it completely transformed to an intriguing body-centered cubic (bcc) structure (phase IV), favorable with uploading pressure up to the maximum pressure of 20.2 GPa in this investigation. Noticeably, phase IV was exactly pointed out as a nonmetallic Bi−Te substitutional alloy that has been well-established by our previous report.33 After decompression, the released ADXRD pattern retrieved its original rhombohedral structure again as depicted in the quenched profile. The strong iron peak arising from T301 stainless-steel gasket led to the depressed intensity of the decompressed samples. In other words, we experimentally identified a pressure-induced reversible phase transition in nanostructured Bi2Te3 HAs and particularly captured a nonmetallic Bi−Te substitutional alloy at a relatively low pressure. With regard to bulk Bi2Te3 materials, the complete transition pressures for phase II and phase IV were estimated to 12.6 and 25.8 GPa, despite the fact that no pure phase III had yet been 3845

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Figure 4. Experimental volumes as a function of applied pressures ranging from ambience to 20.2 GPa for the phases I−IV of nanostructured Bi2Te3 HAs. Results for phase I from ref 33 are also shown for comparison. The dashed lines represent the third-order fitted Birch−Murnaghan EOS functions to the measured P−V data.

Figure 3. Refinements of the experiment (red fork), simulation (blue line), and difference (black line) ADXRD patterns of phase I under ambient conditions (a), phase II at the pressure of 11.9 GPa (b), and phase IV at 15.0 GPa (c) toward nanostructured Bi2Te3 HAs. Therein, green vertical markers indicate the corresponding Bragg reflections.

a slightly increase over the elevating pressure although the lattice constants of both a(b) and c exhibited a declined trend with increasing pressure. It is worth noting that the ambient pressure isothermal bulk modulus B0 for cubic phase IV was so large as even up to 99.9(1) GPa, indicating the highly difficult compressibility. The enhancement of bulk modulus can be ascribed to the higher surface energy contribution in nanostructured Bi2Te3 HAs. Moreover, the remarkable volume shrinkage of 13% for phases I−IV further confirmed the mechanism of large volume collapse should be responsible for the depression of transition pressure toward nanostructured Bi2Te3 HAs. So as to elucidate the transformation process at a glance, Figure 5 depicts schematic illustrations for phases I−IV of nanostructured Bi2Te3 HAs under high-pressure conditions. The crystal structure evolution with pressure unambiguously demonstrated the pressure-induced structural phase transition route of nanostructured Bi2Te3 HAs. Pressure can first break the originally layered structure (phase I) at 9.2 GPa to form more compact structures (phase II) with a larger coordination number as a result of intralayer displacement of Bi2Te3. As the pressure increased to 13.2 GPa, the transformation of phase III can be viewed as a continuously monoclinic distortion from phase II owing to the interlayer compression. Upon further compression to 15.0 GPa, the compound eventually evolved into an ordered bcc structure, accompanied by the disordered occupancy of both Bi and Te (phase IV).

the crystal structure of phase IV to be a bcc unit cell (Figure 3c). This cubic phase strictly follows the extinction rules for space group Im3m ̅ with lattice constant of a = 3.68(2) Å. Meanwhile, the insufficiently strong radiant energy further rendered only (110) and (200) crystal planes appear. Within this structure, Bi and Te atoms are disordered to randomly share the bcc lattice sites, thus forming a Bi−Te substitutional alloy. Although the atomic radii of Bi and Te atoms satisfy the Hume−Rothery rules, the large difference between them is unfavorable to the formation of alloy. Accordingly, pressures herein do offer an additional effective driving force to reduce the disparity of atomic radii between these two components, thereby facilitating such a Bi−Te substitutional alloy. Meanwhile, the intrinsic substitutional point defects regarding antisite BiTe2 in nanostructured Bi2Te3 HAs further give an impetus to the formation of phase IV by adopting a bcc disordered occupancy of Bi and Te atoms. As shown in Figure 4, the experimental P−V data ranging from ambience to 20.2 GPa were fitted by means of the thirdorder Birch−Murnaghan equation of state (EOS):48 P=

−7/3 ⎡ ⎛ V ⎞−5/3⎤ 3B0 ⎢⎛ V ⎞ ⎥ −⎜ ⎟ ⎜ ⎟ ⎥⎦ 2 ⎢⎣⎝ V0 ⎠ ⎝ V0 ⎠

⎧ ⎡⎛ ⎞−2/3 ⎤⎫ ⎪ ⎪ V 3 × ⎨1 + (B0′ − 4)⎢⎜ ⎟ − 1⎥⎬ ⎢⎣⎝ V0 ⎠ ⎥⎦⎪ ⎪ 4 ⎩ ⎭

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CONCLUSION In summary, nanostructured Bi2Te3 HAs underwent a reversible structural phase transition under quasi-hydrostatic conditions by using an ADXRD technique in a DAC apparatus. Four distinct phases I−IV by respectively adopting crystal structures of rhombohedral (I), monoclinic (II, III), and bcc (IV) were experimentally observed with increasing pressure up to 20.2 GPa. Notably, nanostructured Bi2Te3 HAs eventually developed into a Bi−Te substitutional nonmetallic alloy at pressure even as low as 15.0 GPa, approximately 10 GPa lower as compared with conventional bulk counterpart. Drastically reduced transition pressure in the case was attributed to the

where V0 is the zero-pressure volume, B0 is the bulk modulus at ambient pressure, and B0′ is a parameter for pressure derivative. With B′0 fixed as 4, the isothermal bulk modulus B0 for rhombohedral phase I of nanostructured Bi2Te3 HAs was estimated as 52.6(5) GPa, much larger than that of its bulk counterpart (43.7(4) GPa) deduced from ref 33. Apparent volume drop by 9% for phase I−II evidenced the first-order phase transition. In addition, as shown in Figure S3, the c-axis direction of phase I was more sensitive to external pressure with a stark compression rate. Moreover, the ratio of c/a represented 3846

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Figure 5. Schematic illustrations with respect to crystal structures for the phases I−IV of nanostructured Bi2Te3 HAs under high pressure conditions. (4) Song, Y.; Manaa, M. R. New Trends in Chemistry and Materials Science in Extremely Tight Space. J. Phys. Chem. C 2012, 116, 2059− 2060. (5) Sun, L.; Chen, X. J.; Guo, J.; Gao, P. W.; Huang, Q. Z.; Wang, H. D.; Fang, M. H.; Chen, X. L.; Chen, G. F.; Wu, Q.; et al. Re-Emerging Superconductivity at 48 Kelvin in Iron Chalcogenides. Nature 2012, 483, 67−69. (6) Zhang, W.; Oganov, A. R.; Goncharov, A. F.; Zhu, Q.; Boulfelfel, S. E.; Lyakhov, A. O.; Stavrou, E.; Somayazulu, M.; Prakapenka, V. B.; Konôpková, Z. Unexpected Stable Stoichiometries of Sodium Chlorides. Science 2013, 342, 1502−1505. (7) San-Miguel, A. Nanomaterials under High-Pressure. Chem. Soc. Rev. 2006, 35, 876−889. (8) Gurlo, A. Structural Stability of High-Pressure Polymorphs in In2O3 Nanocrystals: Evidence of Stress-Induced Transition? Angew. Chem., Int. Ed. 2010, 49, 5610−5612. (9) Lin, Y.; Yang, Y.; Ma, H.; Cui, Y.; Mao, W. L. Compressional Behavior of Bulk and Nanorod LiMn2O4 under Nonhydrostatic Stress. J. Phys. Chem. C 2011, 115, 9844−9849. (10) Wang, Z.; Wen, X. D.; Hoffmann, R.; Son, J. S.; Li, R.; Fang, C. C.; Smilgies, D. M.; Hyeon, T. Reconstructing a Solid-Solid Phase Transformation Pathway in CdSe Nanosheets with Associated Soft Ligands. Proc. Natl. Acad. Sci. U. S. A. 2010, 107, 17119−17124. (11) Bian, K.; Wang, Z.; Hanrath, T. Comparing the Structural Stability of PbS Nanocrystals Assembled in fcc and bcc Superlattice Allotropes. J. Am. Chem. Soc. 2012, 134, 10787−10790. (12) Wu, H.; Wang, Z. W.; Fan, H. Y. Stress-Induced Nanoparticle Crystallization. J. Am. Chem. Soc. 2014, 136, 7634−7636. (13) Lü, X.; Hu, Q.; Yang, W.; Bai, L.; Sheng, H.; Wang, L.; Huang, F.; Wen, J.; Miller, D. J.; Zhao, Y. S. Pressure-Induced Amorphization in Single-Crystal Ta2O5 Nanowires: A Kinetic Mechanism and Improved Electrical Conductivity. J. Am. Chem. Soc. 2013, 135, 13947−13953. (14) Tolbert, S. H.; Alivisatos, A. P. Size Dependence of a First Order Solid-Solid Phase Transition: The Wurtzite to Rock Salt Transformation in CdSe Nanocrystals. Science 1994, 265, 373−376. (15) Wang, L.; Yang, W. G.; Ding, Y.; Ren, Y.; Xiao, S. G.; Liu, B. B.; Sinogeikin, S. V.; Meng, Y.; Gosztola, D. J.; Shen, G. Y.; et al. SizeDependent Amorphization of Nanoscale Y2O3 at High Pressure. Phys. Rev. Lett. 2010, 105, 095701. (16) Li, B.; Wen, X.; Li, R.; Wang, Z. W.; Clem, P. G.; Fan, H. Y. Stress-Induced Phase Transformation and Optical Coupling of Silver Nanoparticle Superlattices into Mechanically Stable Nanowires. Nat. Commun. 2014, 5, 4179. (17) Wu, H.; Bai, F.; Sun, Z.; Haddad, R. E.; Boye, D. M.; Wang, Z. W.; Huang, J. Y.; Fan, H. Y. Nanostructured Gold Architectures Formed through High Pressure-Driven Sintering of Spherical Nanoparticle Arrays. J. Am. Chem. Soc. 2010, 132, 12826−12828. (18) Wu, H.; Bai, F.; Sun, Z.; Haddad, R. E.; Boye, D. M.; Wang, Z. W.; Fan, H. Y. Pressure-Driven Assembly of Spherical Nanoparticles

synergistic effect involving large volume collapse and the unique 1D nanostructures with intrinsic substitutional point defects regarding antisite BiTe2. Our findings may provide a promising avenue for the development of future multifunctional nanoalloys that comprised nonmetallic elements.

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ASSOCIATED CONTENT

S Supporting Information *

Comparison of hydrostaticities between silicon oil and methanol−ethanol (4:1 by volume) mixture as PTM, investigation of pressure gradient, and pressure-dependent lattice constants of rhombohedral phase Bi2Te3 HAs. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected]; Ph 86-431-85168882; Fax: 86-43185168883 (B.Z.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by NSFC (Nos. 91227202, 11404135, and 11204101), Changbai Mountain Scholars Program (No. 2013007), RFDP (No. 20120061130006), the National Basic Research Program of China (No. 2011CB808200), the China Postdoctoral Science Foundation (Nos. 2014M550171 and 2012M511327), and Jilin Provincial Science & Technology Development Program (No. 20150520087JH). Synchrotron XRD experiments were performed at beamline 15U1 at the Shanghai Synchrotron Radiation Facility (SSRF). Portions of this work were performed at 4W2 HP-Station, Beijing Synchrotron Radiation Facility (BSRF), which is supported by Chinese Academy of Sciences (Grants KJCX2-SW-N20 and KJCX2-SW-N03).

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DOI: 10.1021/jp512565b J. Phys. Chem. C 2015, 119, 3843−3848

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DOI: 10.1021/jp512565b J. Phys. Chem. C 2015, 119, 3843−3848