Chunying Chao

Facile synthesis of single-crystalline mesoporous α-Fe2O3 and Fe3O4 nanorods as anode materials for lithium-ion batteries

In this work, single-crystalline α-FeOOH nanorods with a length of 400–700 nm and a diameter of 20–80 nm were successfully synthesized via a facile template-free hydrothermal method. Single-crystalline mesoporous α-Fe2O3 and Fe3O4 nanorods could be obtained from these α-FeOOH precursors after calcining at 350 °C in air and 500 °C in nitrogen, respectively. The as-prepared single-crystalline mesoporous α-Fe2O3 and Fe3O4 nanorods exhibited a large specific surface area and porosity, effectively enhancing the electrochemical reaction area and accommodate the strain during the charge–discharge cycling process.

Self‐Templated Synthesis of Single‐Crystal and Single‐Domain Ferroelectric Nanoplates

Low-dimensional nanomaterials, such as nanowires and nanotubes, 3] have received extensive attention because of their fascinating catalysis, optics, and electronics 7] properties, which offer the opportunity to fabricate nanodevices. Much attention has been paid to materials with two-dimensional (2D) nanostructure because of their unique electronic, magnetic, and storage properties. In particular, the recent development of stable graphene has stimulated great interest in studying free-standing 2D nanomaterials. So far, a variety of 2D free-standing materials with nanostructure, such as PbS nanosheets, WO3 nanoplates, [10] CeO2 nanoplates, [11] MoS2 nanoflakes, 13] and TiO2 nanosheets, [4] have been successfully synthesized. Compared to these simple compounds, 2D free-standing, single-crystal multicomponent oxide nanomaterials, such as ferroelectric oxides, have been rarely reported because of the relatively complex crystal structures and rigid crystalline properties of these oxides. Ferroelectric oxide nanomaterials, such as PbTiO3 (PT), Pb(Zr,Ti)O3, and BaTiO3, have versatile properties for various technical applications ranging from nonvolatile ferroelectric random access memories (NFERAMs) to electromechanical applications. 15] Among these nanomaterials, 2D free-standing, single-crystal ferroelectric materials are highly attractive because of their potential performances. For example, ultrathin single crystals of BaTiO3 [16,17] prepared by focused ion beam (FIB) microscopy have been used as single-crystal capacitors with thicknesses down to about 65 nm. These ferroelectric platelets fabricated by FIB have greatly improved our understanding of the fundamental properties of thin films. However, recent theoretical research predicts that ferroelectric nanodiscs could even favor an ultimate NFERAM density of 60 10 bits per square inch as well as a new toroid moment. In contrast to the conventional properties, the surface chemistry of ferroelectric oxides only gradually became an active field of research. In particular, it has been predicted that CO and NO catalysis could be favored on ultrathin Pt(100) films supported on ferroelectric PbTiO3. [22] Various methods have so far been applied to fabricate 0D and 1D ferroelectric nanomaterials, including templated methods, sol-gel processing, 28] soft-chemistry routes, solvothermal/hydrothermal reactions, 31] and electrospinning techniques. 33] Despite much effort, there is still an absence of a simple wet-chemistry method to prepare 2D single-crystal ferroelectric nanomaterials, such as nanoplates and nanodiscs. Here we report, for the first time, that freestanding, single-crystal PT nanoplates can be synthesized by a facile hydrothermal method. The characterization of the microstructure by X-ray diffraction (XRD) and high-resolution transmussion electron microscopy (HRTEM) demonstrates that these PT nanoplates, with side lengths of 600– 1100 nm and heights of about 150 nm, grow along the ab plane of the tetragonal perovskite structure and that {001} facets at the top and bottom surfaces are exposed. The “self-templated” crystal growth has been employed to discuss the mechanism for the formation of PT nanoplates under hydrothermal conditions. Electrostatic force microscopy in the dynamic contact mode (DC-EFM) of operation was also used to study the ferroelectric properties of the PT nonaplates. Furthermore, the catalytic performance of the nanoplates for the oxidation of carbon monoxide (CO) has been evaluated. In brief, tetragonal-phase PT nanoplates were synthesized by a hydrothermal method at 200 8C by using 6m KOH. Figure 1a shows a typical XRD pattern (JCPDS 70-0746) of PT nanoplates prepared by the hydrothermal process at 200 8C for 12 h with 6m KOH, and indicates that the product has a pure tetragonal perovskite PT structure. More importantly, the intensity of the (001) diffraction peak is dramatically higher than that of (100), which is opposite to the case in conventional perovskite PT (JCPDS 70-0746). This observation reveals that {001} crystal planes are prevailent in the sample. Scanning electron microscopy (SEM) and TEM analysis show that the products consist of well-defined structures with a rectangular outline and a side length of 600–1100 nm (Figure 1b,c). The HRTEM image (Figure 1d) of a PT nanoplate shows a clear crystal lattice with uniform interplanar spacings of 0.390 nm and 0.390 nm, which correspond to the tetragonal (100) and (010) planes, respectively, and indicate that the PT nanoplates grow along the ab plane of the perovskite structure. The effect of the KOH concen[*] C. Y. Chao, Dr. Z. H. Ren, Z. Xiao, Z. Y. Liu, Dr. G. Xu, J. Q. Mai, Dr. X. Li, Dr. G. Shen, Dr. G. R. Han State Key Laboratory of Silicon Materials Department of Materials Science and Engineering Cyrus Tang Center for Sensor Materials and Application Zhejiang University, Hangzhou 310027 (P.R. China) E-mail: renzh@zju.edu.cn hgr@zju.edu.cn

Size-Controlled Single-Crystal Perovskite PbTiO3 Nanofibers from Edge-Shared TiO6 Octahedron Columns

With the minimization of device sizes, great efforts have been devoted to the synthesis and understanding of ferroelectrics at the nanoscale. [ 3 , 4 ] In particular, one-dimensional (1D) perovskite nanostructures have been the focus of numerous research projects for their potential applications in high-density ferroelectric random access memory, piezoelectricity nanogenerators, and nonlinear optics. [ 5–9 ] As a prototypical perovskite-type ferroelectric, lead titanate (PbTiO 3 ) is a desired system to understand ferroelectricity and ferroelectric phase transformation at the nanoscale because of its simple structure and very large spontaneous polarization. [ 10 , 11 ] Recent experimental results indicate that ferroelectricity could be sustainable in a three unit cell (1.2 nm) thick fi lm of PbTiO 3 at room temperature. [ 4 ] For PbTiO 3 nanowires, an unknown phase transition between the vortex polarization and conventional one mediated by strain and surface terminations has been revealed theoretically. [ 12 , 13 ] It also suggests that ferroelectricity could be enhanced within PbO-terminated PbTiO 3 nanowires, thus leading to a critical size of the nanowire down to only one unit cell. As a comparison, the size effect of single-crystal ferroelectric nanowires has rarely been investigated experimentally. Different methods have been exploited in the last decade to synthesize 1D perovskite oxide nanostructures, such as template preparation, [ 14–18 ] hydrothermal methods, [ 19 , 20 ]

The hydrothermal synthesis and formation mechanism of single-crystalline perovskite BiFeO3 microplates with dominant (012) facets

A facile hydrothermal method has been developed to prepare single-crystal BiFeO3 (BFO) microplates, where the raw material (C6H10BiNO8) was used both as a reactant and a surface modifier. The as-synthesised BFO microplates were dominated by (012) facets with the lateral length of 8 μm and thickness of 510–550 μm. The results of XRD, SEM, TEM, HRTEM and FT-IR indicate that the adsorption behaviour of the organic ligands could play a key role in the formation of the BFO microplates. Moreover, the dielectric constant of the BFO–PVDF film is much higher than the pure BFO at room temperature. The specially chosen raw material (C6H10BiNO8) and the proposed formation mechanism of the BFO microplates could be extended to tailor the crystal growth of the 2D structures of other perovskite oxides.

Facile synthesis of PbTiO3 truncated octahedra via solid-state reaction and their application in low-temperature CO oxidation by loading Pt nanoparticles

Perovskite PbTiO3 (PTO) nanocrystals with a truncated octahedral morphology have been prepared by a facile solid-state reaction. Pt nanoparticles preferentially nucleated on the {111} facet of PTO nanocrystals exhibit a remarkable low-temperature catalytic activity towards CO oxidation from a temperature as low as 30 °C and achieve 100% conversion at ∼50 °C.

Hydrothermal synthesis of single-crystalline tetragonal perovskite PbTiO3 nanosheets with dominant (001) or (111) facets

Single-crystalline tetragonal perovskite PbTiO3 nanosheets are synthesized via a hydrothermal route assisted by NaNO3 and KNO3. Due to the difference in electronegativity, Na+ ions fasten on (001) planes, whereas K+ ions fasten on (111) planes, resulting in PbTiO3 nanosheets with dominant (001) or (111) facets, respectively.

Hydrothermal synthesis of ferroelectric PbTiO3 nanoparticles with dominant {001} facets by titanate nanostructure

A facile hydrothermal method has been developed to synthesize single-crystal ferroelectric PT nanoplates by using K2Ti6O13 nanowires as synthetic precursor. The PT nanoplates with dominant {001} facets have the side length of 500–700 nm and height of 100–150 nm. Piezoelectric force microscopy (PFM) results demonstrated that the PT nanoplates show obvious piezoelectric and ferroelectric activity. Moreover, the crystal growth of the PT nanoplates has been discussed. The results revealed that the gradual dissolution of K2Ti6O13 nanowires in alkali solution and the template of lead oxide are essential to the formation of PT nanoplates.

Length-controlled synthesis and the photoluminescence of pre-perovskite PbTiO3 nanofibers

A novel approach that combines a modified sol–gel process with a PVA-assisted hydrothermal reaction at 200 °C for 12 h has been developed to prepare single-crystal pre-perovskite PbTiO3 nanofibers with good dispersity and length control. By increasing the dosage of triethanolamine (TEA) solution into the Ti precursor to modify the sol–gel process, the length of the nanofibers in the prepared samples decreased from about 35–90 μm to 5–12 μm, whereas the corresponding diameter remained in the range of 100–300 nm. Further, the dispersity of the samples, as well as the diameter uniformity of a single nanofiber, was improved significantly. In particular, a broad green photoluminescence (PL) emission (~550 nm) was observed in the nanofibers at room temperature. It is interesting to find that no obvious size effect was detected on the green PL emission.