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Ultrahigh Energy Storage Performance of Lead‐Free Oxide Multilayer Film Capacitors via Interface Engineering

Ultrahigh energy storage density of 52.4 J cm-3 with optimistic efficiency of 72.3% is achieved by interface engineering of epitaxial lead-free oxide multilayers at room temperature. Moreover, the excellent thermal stability of the performances provides solid basis for widespread applications of the thin film systems in modern electronic and power modules in harsh working environments.

Strain-tunable magnetic properties of epitaxial lithium ferrite thin film on MgAl2O4 substrates

Epitaxial LiFe5O8 thin films with various thicknesses were fabricated on (001) MgAl2O4 substrates by using a high-pressure sputtering system. All the LiFe5O8 thin films have excellent epitaxial quality with ordered α-LiFe5O8 structure, and larger in-plane compressive and out-of-plane tensile strain can be obtained by decreasing the film thickness. Moreover, the in-plane compressive strain can significantly induce the enhancement of in-plane magnetization while the out-of-plane tensile strain tends to reduce the out-of-plane magnetization. It indicates that controlling the thickness of the films is an effective method to tailor the interface strain and further modify the magnetic properties of the epitaxial LiFe5O8 thin films.

Flexible Quasi-Two-Dimensional CoFe2O4 Epitaxial Thin Films for Continuous Strain Tuning of Magnetic Properties

Epitaxial thin films of CoFe2O4 (CFO) have successfully been transferred from a SrTiO3 substrate onto a flexible polyimide substrate. By bending the flexible polyimide, different levels of uniaxial strain are continuously introduced into the CFO epitaxial thin films. Unlike traditional epitaxial strain induced by substrates, the strain from bending will not suffer from critical thickness limitation, crystalline quality variation, and substrate clamping, and more importantly, it provides a more intrinsic and reliable way to study strain-controlled behaviors in functional oxide systems. It is found that both the saturation magnetization and coercivity of the transferred films can be changed over the bending status and show a high accord with the movement of the curvature bending radius of the polyimide substrate. This reveals that the mechanical strain plays a critical role in tuning the magnetic properties of CFO thin films parallel and perpendicular to the film plane direction.

Phase stability and B-site ordering in La2NiMnO6 thin films

Thin films of multiferroic double-perovskite La2NiMnO6 are prepared on (001)-oriented SrTiO3, (La0.289Sr0.712)(Al0.633Ta0.356)O3, and LaSrAlO4 substrates by pulsed laser deposition. Microstructure investigation by advanced electron microscopy shows that the La2NiMnO6 films have a monoclinic structure on the SrTiO3 substrates and a rhombohedral structure on the (La0.289Sr0.712)(Al0.633Ta0.356)O3 and LaSrAlO4 substrates. Atomic-scale elemental maps of the monoclinic and rhombohedral phases reveal a short-range and/or partial ordering of the B-sites. In addition, domains and columnar grains are found in the films. Our results demonstrate that the phase and microstructure of the La2NiMnO6 films can be tuned by epitaxial strains induced by different substrates.

Anatomy of vertical heteroepitaxial interfaces reveals the memristive mechanism in Nb2O5-NaNbO3 thin films

Dynamic oxygen vacancies play a significant role in memristive switching materials and memristors can be realized via well controlled doping. Based on this idea we deposite Nb2O5-NaNbO3 nanocomposite thin films on SrRuO3-buffered LaAlO3 substrates. Through the spontaneous phase separation and self-assembly growth, two phases form clear vertical heteroepitaxial nanostructures. The interfaces between niobium oxide and sodium niobate full of ion vacancies form the conductive channels. Alternative I-V behavior attributed to dynamic ion migration reveals the memristive switching mechanism under the external bias. We believe that this phenomenon has a great potential in future device applications.

Large Energy Density, Excellent Thermal Stability, and High Cycling Endurance of Lead-Free BaZr0.2Ti0.8O3 Film Capacitors

A large energy storage density (ESD) of 30.4 J/cm3 and high energy efficiency of 81.7% under an electrical field of 3 MV/cm was achieved at room temperature by the fabrication of environmentally friendly lead-free BaZr0.2Ti0.8O3 epitaxial thin films on Nb-doped SrTiO3 (001) substrates by using a radio-frequency magnetron sputtering system. Moreover, the BZT film capacitors exhibit great thermal stability of the ESD from 16.8 J/cm3 to 14.0 J/cm3 with efficiency of beyond 67.4% and high fatigue endurance (up to 106 cycles) in a wide temperature range from room temperature to 125 °C. Compared to other BaTiO3-based energy storage capacitor materials and even Pb-based systems, BaZr0.2Ti0.8O3 thin film capacitors show either high ESD or great energy efficiency. All of these excellent results revealed that the BaZr0.2Ti0.8O3 film capacitors have huge potential in the application of modern electronics, such as locomotive and pulse power, in harsh working environments.

Enhanced energy density with a wide thermal stability in epitaxial Pb0.92La0.08Zr0.52Ti0.48O3 thin films

High-quality epitaxial Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films of thickness of ∼880u2009nm were fabricated using pulsed laser deposition on (001) Nb doped SrTiO3 (Nb:STO) substrates. Besides a confirmation of the epitaxial relationship [100]PLZT//[100]Nb:STO and (001)PLZT//(001)Nb:STO using X-ray diffraction, a transmission electron microscopy study has revealed a columnar structure across the film thickness. The recoverable energy density (Wrec) of the epitaxial PLZT thin film capacitors increases linearly with the applied electric field and the best value of ∼31u2009J/cm3 observed at 2.27 MV/cm is considerably higher by 41% than that of the polycrystalline PLZT film of a comparable thickness. In addition to the high Wrec value, an excellent thermal stability as illustrated in a negligible temperature dependence of the Wrec in the temperature range from room temperature to 180u2009°C is achieved. The enhanced Wrec and the thermal stability are attributed to the reduced defects and grain boundaries in epitaxial PLZT ...

Epitaxial Lift‐Off of Centimeter‐Scaled Spinel Ferrite Oxide Thin Films for Flexible Electronics

Mechanical flexibility of electronic devices has attracted much attention from research due to the great demand in practical applications and rich commercial value. Integration of functional oxide materials in flexible polymer materials has proven an effective way to achieve flexibility of functional electronic devices. However, the chemical and mechanical incompatibilities at the interfaces of dissimilar materials make it still a big challenge to synthesize high-quality single-crystalline oxide thin film directly on flexible polymer substrates. This study reports an improved method that is employed to successfully transfer a centimeter-scaled single-crystalline LiFe5 O8 thin film on polyimide substrate. Structural characterizations show that the transferred films have essentially no difference in comparison with the as-grown films with respect to the microstructure. In particular, the transferred LiFe5 O8 films exhibit excellent magnetic properties under various mechanical bending statuses and show excellent fatigue properties during the bending cycle tests. These results demonstrate that the improved transfer method provides an effective way to compose single-crystalline functional oxide thin films onto flexible substrates for applications in flexible and wearable electronics.

Synthesis of Hierarchical Sb2MoO6 Architectures and Their Electrochemical Behaviors as Anode Materials for Li-Ion Batteries.

We report a facile microwave-hydrothermal synthesis of hierarchical Sb2MoO6 architectures assembled from single-crystalline nanobelts, which are first demonstrated as anode materials for lithium-ion batteries (LIBs) with superior electrochemical properties. Sb2MoO6 delivers a high initial reversible capacity of ∼1140 mA h/g at 200 mA/g with large initial Coulombic efficiency of ∼89%, and a reversible capacity of ∼878 mA h/g after 100 cycles at 200 mA/g. As a new anode, the electrochemical behaviors are investigated through ex situ TEM and XPS measurements, revealing that the superior electrochemical performance is attributed to the novel hierarchical structures and the synergistic interaction between both the active Sb- and Mo-species, in which the in situ generated Li2O-MoOx serves as matrix and efficiently buffers the volume changes of the Li-Sb alloying-dealloying upon cycling.

A general soft-enveloping strategy in the templating synthesis of mesoporous metal nanostructures

Metal species have a relatively high mobility inside mesoporous silica; thus, it is difficult to introduce the metal precursors into silica mesopores and suppress the migration of metal species during a reduction process. Therefore, until now, the controlled growth of metal nanocrystals in a confined space, i.e., mesoporous channels, has been very challenging. Here, by using a soft-enveloping reaction at the interfaces of the solid, liquid, and solution phases, we successfully control the growth of metallic nanocrystals inside a mesoporous silica template. Diverse monodispersed nanostructures with well-defined sizes and shapes, including Ag nanowires, 3D mesoporous Au, AuAg alloys, Pt networks, and Au nanoparticle superlattices are successfully obtained. The 3D mesoporous AuAg networks exhibit enhanced catalytic activities in an electrochemical methanol oxidation reaction. The current soft-enveloping synthetic strategy offers a robust approach to synthesize diverse mesoporous metal nanostructures that can be utilized in catalysis, optics, and biomedicine applications.Metal species are highly mobile within mesoporous silica, making it difficult to template growth of metallic nanocrystals inside the channels. Here, the authors introduce a solid-liquid-solution interfacial strategy to suppress migration of the metal species, achieving control over a variety of mesostructured nanomaterials.