We report a continuously tunable resistive switching behavior in Pt/BiFeO 3 /Nb-doped SrTiO 3 heterostructure for ferroelectric memristor application. The resistance of this memristor can be tuned up to 5 Â 10 5 % by applying voltage pulses at room temperature, which exhibits excellent retention and anti-fatigue characteristics. The observed memristive behavior is attributed to the modulation effect of the ferroelectric polarization reversal on the width of depletion region and the height of potential barrier of the p-n junction formed at the BiFeO 3 /Nb-doped SrTiO 3 interface.

We report the synthesis and characterization of ordered multiferroic BiFeO 3 ͑BFO͒ nanotube arrays. BFO nanotubes with diameters of about 250 nm and lengths of about 6 m were fabricated by means of a sol-gel method utilizing nanochannel alumina templates. After postannealing at 700°C, the BFO nanotubes exhibited a polycrystalline microstructure, and x-ray diffraction and transmission electron microscopy study revealed that they are of a perovskite crystal structure. Significant ferroelectric and piezoelectric characteristics of BFO nanotubes have been demonstrated by means of piezoresponse force microscopy measurement. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.2076437͔The prospect of a new generation of random access memory technology to handle the growing demand for memory is pushing several research fronts in this area, 1-4 such as magnetic random access memory and ferroelectric random access memory. Magnetism is involved with the local spin of electrons, while ferroelectricity represents a cooperative phenomenon that relies on the interaction of neighboring permanent electric dipoles in a crystal lattice. These two phenomena can coexist in some unusual perovskite-type oxide materials including magnetic elements, such as BiFeO 3 , 5-7 BiMnO 3 , 8,9 and TbMnO 3 , 10,11 termed multiferroics. Multiferroics have attracted much attention because of their promise in the realization of a new type of memory by a combination of ferroelectric and ferromagnetic properties. As the development of nanoscale electronics approaches a practical stage, it is quite natural to ask how the crystal structure and state of polarization are influenced by the shape and size of multiferroic materials. The synthesis of multiferroic nanostructures with a controllable size and shape is critical not only in new device application, such as high-density magnetically recorded ferroelectric memory, but also from a fundamental point of view.BiFeO 3 ͑BFO͒ is known to have rhombohedrally distorted perovskite structure. The space group R3c of BFO allows for a ferroelectric atomic displacement of below 1083 K and a weak ferromagnetism of below a Néel temperature T N of 643 K simultaneously. The enhancement of polarization and related properties in heteroepitaxially constrained BFO films with a thickness of 200 nm has been reported. The films display a room-temperature spontaneous polarization almost of an order of magnitude higher than that of the bulk. 3,12 More recently, a giant ferroelectric polarization of beyond 150 C/cm 2 has been obtained in BFO thin film deposited on a Pt/ TiO 2 / SiO 2 / Si substrate at 90 K. 13 Ordered BFO nanostructure arrays are of considerable interest for future applications, such as a vertical magnetic recording with an ultrahigh recording density. In this letter, we report the synthesis of the BFO nanotube arrays by using a sol-gel template method. Significant ferroelectric and piezoelectric characteristics of the BFO nanotube arrays have been revealed.Nanochannel alumina ͑NCA͒ templates were prepared by ...

We report the synthesis and characterization of ferroelectric lead zirconate titanate Pb͑Zr 0.53 Ti 0.47 ͒O 3 (PZT) nanowires. The PZT nanowires, with diameters of about 45 nm and lengths of about 6 m, were fabricated by means of a sol-gel method utilizing nanochannel alumina templates. After postannealing at 700°C, the PZT nanowires exhibit a polycrystalline microstructure, and x-ray diffraction and transmission electron microscopy study revealed their perovskite crystal structure. Recently, increasing efforts have been made to synthesize and understand ferroelectric nanostructures because of the promise they show in the realization of nanoscale piezoelectric transducers and actuators, ultrasonic devices, and nonvolatility memory devices. [1][2][3][4][5] As ferroelectricity represents a cooperative phenomenon that relies on the interaction of neighboring permanent electric dipoles in a crystal lattice, there is a size limit, known as the superparaelectric limit, below which ferroelectricity vanishes. Therefore, the synthesis of ferroelectric nanostructures of a controllable size and shape is of great interest not only for future applications but also from a fundamental point of view. Urban and coworkers have reported earlier the synthesis of BaTiO 3 and SrTiO 3 nanorods with diameters ranging from 5 to 60 nm by a solution-phase decomposition of bimetallic alkoxide precursors in the presence of coordinating ligands.6 Using a sol-gel template method of synthesis, Hernandez et al. have fabricated BaTiO 3 and PbTiO 3 nanotubes within 200 nm alumina templates.7 Some interesting properties have also been found in ferroelectric nanowires. For example, BaTiO 3 nanowires as small as 10 nm in diameter still retain ferroelectricty, and nonvolatile polarization domains as small as 100 nm 2 in size can be induced on BaTiO 3 nanowires. This suggests that ferroelectric nanowires may be used to fabricate nonvolatile memory devices with an integration density approaching 1 terabit/ cm 2 . 8Lead zirconate titanate Pb͑Zr 0.53 Ti 0.47 ͒O 3 (PZT) is a ferroelectric material that possesses a perovskite crystal structure, and shows a high potential for applications in device due to its high dielectric constant, high Curie temperature, and high breakdown strength. PZT nanotubes have been obtained within silicon and nanochannel alumina (NCA) templates by using several different deposition techniques, including misted chemical solution deposition and pore wetting. 3,9 In this letter, we report the synthesis of the PZT nanowires by using a sol-gel template method. We choose NCA as the template because the pore diameters of the NCA template can be well controlled from several hundreds of nanometers to 5 nm. Ferroelectric properties have been demonstrated in individual PZT nanowires by using piezoresponse force microcopy (PFM).NCA templates were prepared by means of anodization, 10,11 and the PZT nanowires were synthesized by sol-gel method utilizing the NCA templates. A PZT sol-gel precursor was prepared according to a previous report, 12...

Systematic understanding of the crucial roles of the atomic coordination, stacking and arrangement of metal-based electrocatalysts in the alkaline HOR process is provided.

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