Xinhua Zhu

Perovskite oxide nanotubes: synthesis, structural characterization, properties and applications

Perovskite oxides exhibit a wide range of functional properties, such as ferroelectricity, piezoelectricity, pyroelectricity, non-linear dielectric behavior, as well as multiferroic property. These properties are indispensable for applications in microelectronic devices. Recent advances in science and technology of perovskite oxides have resulted in the feature sizes of microelectronic devices down-scaling into nanoscale dimensions. At the nanoscale perovskite oxides display novel physical properties that are different from their bulk and film counterparts. Understanding these size effects of perovskite oxides at the nanoscale is of importance for the developing a new generation of revolutionary electronic nanodevices. Due to these effects being dependent on the structure and finite size, considerable efforts have been made in the controllable synthesis of low-dimensional perovskite nanostructures such as perovskite oxide nanotubes (PONTs). PONTs can not only be used as building blocks for miniaturized microelectronic devices, but also offer fundamental scientific opportunities for investigating the intrinsic size effects of physical properties. This review article describes the recent progress made in the field of PONTs, which covers their synthesis, structural characterization, properties and applications. We begin this review with a comprehensive survey on the research activities on PONTs, and then focus on their synthesis strategies. Structural characterization and multifunctional properties of the PONTs prepared by the template synthesis are also summarized. Their potential applications in 3D memory devices, nano-scale fluidic control systems, nanoscale power generators and terahertz generators, are discussed. Finally, we conclude this review by providing our perspectives to the future directions of PONTs.

Microdisplacement characteristics and microstructures of functionally graded piezoelectric ceramic actuator

Abstract In this work, we report a functionally gradient piezoelectric ceramic actuator with sandwiched structure prepared by the powder metallurgical method. The functional gradients of piezoelectric activity and dielectric activity vary inversely across the thickness of the actuator. Such functional gradients are obtained by interdiffusion reaction between a high piezoelectric composition [Pb(Zr,Ti)O 3 /PZT] and a high dielectric composition (PbNi 1/3 Nb 2/3 O 3 /PNN). The bending displacement at the free end of the PNN/PZT functionally graded piezoelectric ceramic actuator was approximately 20 m when 1.4-kV/mm electric field was applied. The grain morphology and compositional distribution across the actuator section and the microstructures of the sandwiched layer were investigated by scanned electron microscopy equipped with energy-dispersive spectroscopy, transmission electron microscopy, and selected area electron diffraction patterns, respectively.

Epitaxial growth and dielectric properties of functionally graded (Ba1−xSrx)TiO3 thin films with stoichimetric variation

Functionally graded (Ba1−xSrx)TiO3 (BST) thin films with stoichimetric variation (x:0.0–0.25) were layer-by-layer grown epitaxially on MgO (100) single-crystal substrates with 100-nm-thick conductive La0.5Sr0.5CoO3 (LSCO) as the bottom electrode by pulsed-laser deposition. X-ray diffraction, rocking curve, and φ scans showed that the graded films are epitaxial grown with an orientation of [001](100)BST//[001](100)MgO. The surface roughness of the up-graded film was larger than that of the down-graded films, and the full width at half maximum of the BST (200) rocking curve of up-graded films was wider than that of the down-graded films. The compositional gradations along the depth in the films were confirmed by Rutherfold backscattering spectroscopy. Dielectric properties measured by vertical structures using LSCO as the bottom electrodes showed that the dielectric constant and dielectric loss at 10 kHz were 532 and 0.010 for the up-graded films, and 715 and 0.0103 for the down-graded films, respectively. ...

Structural, spectroscopic, and dielectric characterizations of Mn-doped 0.67BiFeO 3 –0.33BaTiO 3 multiferroic ceramics

Abstract0.67BiFeO3-0.33BaTiO3 multiferroic ceramics doped with x mol% MnO2 (x = 2–10) were synthesized by solid-state reaction. The formation of a perovskite phase with rhombohedral symmetry was confirmed by X-ray diffraction (XRD). The average grain sizes were reduced from 0.80 μm to 0.50 μm as increasing the Mn-doped levels. Single crystalline nature of the grains was revealed by high-resolution transmission electron microscopy (HRTEM) images and electron diffraction patterns. Polar nano-sized ferroelectric domains with an average size of 9 nm randomly distributed in the ceramic samples were revealed by TEM images. Ferroelectric domain lamellae (71° ferroelectric domains) with an average width of 5 nm were also observed. Vibrational modes were examined by Raman spectra, where only four Raman peaks at 272 cm−1 (E-4 mode), 496 cm−1 (A1-4 mode), 639 cm−1, and 1338 cm−1 were observed. The blue shifts in the E-4 and A1-4 Raman mode frequencies were interpreted by a spring oscillator model. The dieletric constants of the present ceramics as a function of the Mn-doped levels exhibited a V-typed curve. They were in the range of 350–700 measured at 103 Hz, and the corresponding dielectric losses were in range of 0.43–0.96, approaching to 0.09 at 106 Hz.

Domain morphology evolution associated with the relaxor–normal ferroelectric transition in the Bi- and Zn-modified Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 system☆

Abstract To understand the dielectric behavior from a viewpoint of domain configuration, the domain morphology evolution in (Pb0.985Bi0.01)(Ni1/4Zn1/12Nb2/3)0.2(Zr1-σTiσ)0.8O3 ceramics (0.30⩽σ⩽0.60) has been investigated by transmission electron microscopy and high resolution electron microscopy. The results indicated that the domain morphology evolved from the normal micron-sized domains to herringbone domain patterns, and finally to the polar nanodoamains approximately 3∼6 nm in size when the PT content was decreased from 60 to 30 mol%. The normal twin-related 90° macrodomains are closely correlated with the normal dielectric response of the composition with higher PT content, whereas the relaxor response of the composition with lower PT content is directly attributable to nanometer domains that contain 1:1 short-range ordering on the B-site sub-lattice. A model is proposed to describe the effect of the PbTiO3 content on the ferroelectric domain morphology evolution in the system.

Characterization of multiferroic domain structures in multiferroic oxides

Multiferroic oxides have been received much attention due to that these materials exhibit multiple ferroic order parameters (e.g., electric polarization in ferroelectrics, magnetization in ferromagnetics, or spontaneous strain in ferroelastics) simultaneously in the same phase in a certain temperature range, which offer an exciting way of coupling between the ferroic order parameters. Thus, this provides a possibility for constructing new type of multifunctional devices. The multiferroic domain structures in these materials are considered to be an important factor to improve the efficiency and performance of future multiferroic devices. Therefore, the domain structures in multiferroic oxides are widely investigated. Recent developments in domain characterization techniques, particularly the aberration-corrected transmission electron microscopy (TEM), have enabled us to determine the domain structures at subangstrom scale, and the recent development of in situ TEM techniques allows ones to study the dynamic behaviors of multiferroic domains under applied fields or stress while the atomic structure is imaged directly. This paper provides a review of recent advances on the characterization of multiferroic domain structures in multiferroic oxides, which have been achieved by the notable advancement of aberration-corrected TEM.

Dissociation of grain boundary dislocations in SrBi2Ta2O9 ferroelectric thin films

In this work, the dissociation of grain boundary dislocations (GBDs) is reported in SrBi2Ta2O9 (SBT) ferroelectric thin films with c-axis orientation grown by pulsed-laser deposition on Pt/TiO2/SiO2/Si(100) substrates. Small-angle (8.2°) [001] tilt grain boundaries with a boundary plane close to the (110) plane exhibit partial GBDs separated by stacking faults. The dissociated grain-boundary structures have twice the number of GBDs and interdislocation core channel width smaller than that Frank’s geometrical rule predicts. At the equilibrium, the repulsive elastic force between partial dislocations is balanced by an attractive force produced by the formation of a stacking fault between the partials. Based on this, the stacking fault energy is evaluated to be 0.27–0.29 J/m2. The relationship between the leakage current of SBT films and dissociation of GBDs is also discussed.

One-Dimensional Perovskite Manganite Oxide Nanostructures: Recent Developments in Synthesis, Characterization, Transport Properties, and Applications

One-dimensional nanostructures, including nanowires, nanorods, nanotubes, nanofibers, and nanobelts, have promising applications in mesoscopic physics and nanoscale devices. In contrast to other nanostructures, one-dimensional nanostructures can provide unique advantages in investigating the size and dimensionality dependence of the materials’ physical properties, such as electrical, thermal, and mechanical performances, and in constructing nanoscale electronic and optoelectronic devices. Among the one-dimensional nanostructures, one-dimensional perovskite manganite nanostructures have been received much attention due to their unusual electron transport and magnetic properties, which are indispensable for the applications in microelectronic, magnetic, and spintronic devices. In the past two decades, much effort has been made to synthesize and characterize one-dimensional perovskite manganite nanostructures in the forms of nanorods, nanowires, nanotubes, and nanobelts. Various physical and chemical deposition techniques and growth mechanisms are explored and developed to control the morphology, identical shape, uniform size, crystalline structure, defects, and homogenous stoichiometry of the one-dimensional perovskite manganite nanostructures. This article provides a comprehensive review of the state-of-the-art research activities that focus on the rational synthesis, structural characterization, fundamental properties, and unique applications of one-dimensional perovskite manganite nanostructures in nanotechnology. It begins with the rational synthesis of one-dimensional perovskite manganite nanostructures and then summarizes their structural characterizations. Fundamental physical properties of one-dimensional perovskite manganite nanostructures are also highlighted, and a range of unique applications in information storages, field-effect transistors, and spintronic devices are discussed. Finally, we conclude this review with some perspectives/outlook and future researches in these fields.

Gas sensing property and microstructure of SnO2 nanocrystalline prepared by solid state reaction—thermal oxidation

Abstract Nanocrystalline SnO 2 powders have been synthesized by two-step solid state reaction technique. Firstly, the brown SnO particles were obtained by grinding mixed SnCl 2 ·2H 2 O and KOH powders at room temperature. Then, the powders were calcined in air (thermal oxidation) to form the SnO 2 nanoparticles. The phase compositions and microstructures of the product were examined by thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM), respectively. Furthermore, we have measured the gas-sensing property of the products and found its distinct selectivity towards ethanol at the presence of gasoline and acetylene, which is different from the property of pure SnO 2 nanoparticles. The mechanism of such a specificity was discussed briefly.

Characteristics of SrBi2Ta2O9 thin films prepared by pulsed laser deposition for non-volatile memory applications

Abstract Ferroelectric SrBi 2 Ta 2 O 9 (SBT) thin films were prepared on Pt/TiO 2 /SiO 2 /Si(100) substrates by pulsed laser ablation of SrBi 2.2 Ta 2 O 9 ceramic target. The ferroelectric properties and microstructure of SBT films were investigated in this work. The SBT films deposited at 650°C exhibited a remnant polarization of 6.6 μC/cm 2 and a coercive field of 23 kV/cm at 5 V. Higher leakage current was observed in films deposited at 550°C. Crystallinity of the films was examined by X-ray diffraction patterns and no secondary phases were observed. Furthermore, XRD patterns also indicated a change in orientation from c- axis dominated to randomly polycrystalline, when the deposition temperature was changed from 550 to 650°C. Grains in SBT film show polyhedral morphologies based on planar TEM analysis. The microstructures of grain boundaries in SBT film with c -axis dominated orientation were investigated by high-resolution transmission electron microscopy (HRTEM). The relationship between the leakage current of film and microstructures of grain boundaries is briefly discussed.