Tieyu Sun

Large Energy Storage Density and High Thermal Stability in a Highly Textured (111)-Oriented Pb0.8Ba0.2ZrO3 Relaxor Thin Film with the Coexistence of Antiferroelectric and Ferroelectric Phases.

A highly textured (111)-oriented Pb0.8Ba0.2ZrO3 (PBZ) relaxor thin film with the coexistence of antiferroelectric (AFE) and ferroelectric (FE) phases was prepared on a Pt/TiOx/SiO2/Si(100) substrate by using a sol-gel method. A large recoverable energy storage density of 40.18 J/cm(3) along with an efficiency of 64.1% was achieved at room temperature. Over a wide temperature range of 250 K (from room temperature to 523 K), the variation of the energy density is within 5%, indicating a high thermal stability. The high energy storage performance was endowed by a large dielectric breakdown strength, great relaxor dispersion, highly textured orientation, and the coexistence of FE and AFE phases. The PBZ thin film is believed to be an attractive material for applications in energy storage systems over a wide temperature range.

Giant Electric Energy Density in Epitaxial Lead‐Free Thin Films with Coexistence of Ferroelectrics and Antiferroelectrics

Ferroelectrics/antiferroelectrics with high dielectric breakdown strength have the potential to store a great amount of electrical energy, attractive for many modern applications in electronic devices and systems. Here, it is demonstrated that a giant electric energy density (154 J cm−3, three times the highest value of lead-based systems and five times the value of the best dielectric/ferroelectric polymer), together with the excellent fatigue-free property, good thermal stability, and high efficiency, is realized in pulsed laser deposited (Bi1/2Na1/2)0.9118La0.02Ba0.0582(Ti0.97Zr0.03)O3 (BNLBTZ) epitaxial lead-free relaxor thin films with the coexistence of ferroelectric (FE) and antiferroelectric (AFE) phases. This is endowed by high epitaxial quality, great relaxor dispersion, and the coexistence of the FE/AFE phases near the morphotropic phase boundary. The giant energy storage effect of the BNLBTZ lead-free relaxor thin films may make a great impact on the modern energy storage technology.

Controlling the Electromagnetic Field by Indefinite Media with Extremely Strong Anisotropy

In this work, we show how to manipulate the electromag- netic wave at will by using an indeflnite medium with extremely strong anisotropy. The negative element in the indeflnite permittivity tensor goes to the negative inflnity while the positive element is equal to 1, which stretches the hyperbolic equifrequency contour into a straight line type. The direction of the Poynting vector and the wave vector is aligned by the straight line type equifrequency contour along the orientation of the extremely negative permittivity, thus control the wave propagation. The other permittivity of 1 makes the indeflnite medium matched with the air. Moreover, because of the hyperbolic equifrequency contour, evanescent wave can also transmit in the indef- inite medium under the propagation mode, implying the possibility of controlling an evanescent wave by this special indeflnite medium. Sim- ulations are performed to demonstrate the controlling performance and a potential design to realize such a medium by metamaterial with mul- tilayered metal/dielectric structure. This work may supply a shortcut for those former devices based on the Transformation optics.

Estimation of the magnetoelectric coefficient of a piezoelectric-magnetostrictive composite via finite element analysis

We proposed a new approach for estimating the magnetoelectric coefficient of magnetostrictive/piezoelectric composites via finite element analysis. With this method, the relationship between inputting magnetic field and outputting electric polarization for magnetoelectric composites could be directly calculated. This method offers efficient calculation and is applicable for magnetoelectric composites with any complex structures without restrictions on their connectivity and structures. As examples, the magnetoelectric coefficients of 1-3 type and 0-3 type composites were calculated and the results were found to agree well with literature data.

Evidencing the structural conversion of hydrothermally synthesized titanate nanorods by in situ electron microscopy

Despite the high potential of using hydrothermal methods in the industrial production of TiO2 one-dimensional nanostructures (nanotubes, nanowires, etc.) for either environmental or energy applications, there has been much debate on the crystalline structure of the resultant hydrothermal product due to its weak crystallinity and small size. As a result, a range of titanates have been proposed as possible structures for the as-synthesized product. Herein, by using in situ transmission electron microscopy and a highly stable heating system, we microscopically explore the hydrothermally synthesized TiO2-derived single-crystal nanorods and their subsequent structural conversion upon annealing. In our case, a full set of evidence obtained from chemical, crystallographic, and valence state analyses suggests that the as-synthesized product possesses a Na0.8Ti4O8 structure, and undergoes a monoclinic-to-monoclinic transition (topochemical transformation) towards TiO2 (B) via desodiation and reorientation of TiO6 octahedra under constant heating. The as-observed kinetic restructuring process is further examined through density functional theory calculations, revealing the energy-favourable nature of the process. Such an observation at high spatial resolution demonstrates itself as an effective complement to conventional characterization methods, and may pave the way for large-scale synthesis of TiO2-based nanostructures.

Helix-like structure formation of a semi-flexible chain confined in a cylinder channel

Molecular dynamics method is used to study the conformation behavior of a semi-flexible polymer chain confined in a cylinder channel. A novel helix-like structure is found to form during the simulation. Moreover, the detailed characteristic parameters and formation probability of these helix-like structures under moderate conditions are investigated. We find that the structure is not a perfect helix, but a bundle of elliptical turns. In addition, we conduct a statistical analysis for the chain monomer distribution along the radial direction. This research contributes to our understanding of the microscopic conformation of polymer chains in confined environments filled with a solvent.