Yunli Wang

A distinct mutual phase transition in a new PVDF based lead-free composite film with enhanced dielectric and energy storage performance and low loss

Environment-friendly polyvinylidene fluoride (PVDF) based composite films were fabricated by using a high permittivity lead-free Ba(Sn,Ti)O3–(Ba,Ca)TiO3 (BCTS) ceramic filler with a special ‘tricritical’ phase structure. The dielectric and energy storage performance and the microstructure evolution of the samples were investigated. Infrared spectroscopy, X-ray diffraction (XRD) and synchrotron radiation XRD results showed that the plate-shaped BCTS nanopowders induced a distinct mutual phase transition but not the usual nonpolar to polar one. Consequently, a largely increased dielectric constant (er), a higher energy density (∼4 J cm−3 at 200 kV mm−1) and a dielectric loss even lower than that of neat PVDF were simultaneously achieved with a very small loading (0.59 vol%) of BCTS. Theoretical simulations showed that er was well predicted by the effective medium theory and the modified Lichtenecker model, implying the important role of the size and shape of filler particles in performance. A special transitional stratification layer observed around the BCTS particles implies heterogeneous nucleation of the polymer. A mechanism due to the interplay of crystallization and possible stress and electrostatic interaction was proposed to explain the phase evolution. The results may provide new insight into the understanding of the structural characteristics of the composites and a new strategy for tailoring their performance.

Low-cost (0.1BiYbO3-0.9PbTiO3)-PbZrO3-xMn high Curie temperature piezoelectric ceramics with improved high-temperature performance

Here, we report the structure and performance of a low-cost high Curie temperature (TC) Mn-doped ternary BiYbO3-Pb(Zr,Ti)O3 (BY-PZT-xMn) perovskite piezoelectric ceramic system. The partial substitution of Mn for the A-site Pb, B-site Ti and Zr of the ternary system enhanced both the piezoelectric coefficient and the mechanical quality factor, indicating that the variable valence element induced combinatory soft and hard doped characteristics. The improved electrical performance was found to be related to the improved density and homogeneity, and a correlation between the piezoelectricity and the grain size was also observed. More importantly, a Mn doping level of less than 0.8 mol. % also obviously enhanced the thermal stability of the samples, as reflected by the higher TC and depolarization temperature (Td) measured via both in situ Berlincourt method and annealing experiments, and a correlation between TC and tetragonality of BY-PZT-xMn system was observed. The sample with 0.8 mol. % Mn showed a remar...

Determination of surface roughness of InP (001) wafers by x‐ray scattering

The surface roughness of polished InP (001) wafers were examined by x‐ray reflectivity and crystal truncation rod (CTR) measurements. The root‐mean‐square roughness and the lateral correlation scale were obtained by both methods. The scattering intensities in the scans transverse to the specular reflection rod were found to contain two components. A simple surface model of surface faceting is proposed to explain the experimental data. The sensitivities of the two methods to the surface structure and the role of the resolution functions in the CTR measurements are discussed.

P(VDF-TrFE) nanorod assemblies with anisotropic piezoelectric properties investigated by piezoelectric response microscopy

Highly ordered assemblies of the copolymer of vinylidene fluoride and trifluoroethylene P(VDF-TrFE) nanorods with anisotropic piezoelectric response were fabricated on different substrates by using a template-free self-organization method. The significant difference in vertical and lateral piezoelectric responses of the nanorods in piezoresponse force microscopy (PFM) revealed that their molecular dipoles were preferentially oriented parallel to the substrate plane. In addition, dipole orientation distribution map in the nanorods was derived by analyzing the vertical and lateral PFM amplitude and phase images. Infrared reflection spectra further showed that the macromolecular backbones were oriented perpendicularly relative to the substrate. A flat-on lamellar structure and a confined crystallization of dewetted melt phase nanorod formation mechanism were proposed. The highly anisotropic piezoelectric response of the assemblies of nanorods may be promising for nanoscale devices for application in energy h...

New modulation structures observed in Bi2.13Sr1.87CuO6+delta superconductors

A new two-dimensional structure modulation along c- and b-axes has been discovered in superconducting single crystals of Bi2.13Sr1.87CuO6+delta (Bi2201) by x-ray scattering. Such modulation structure does not exist in non-superconducting Bi2201 single crystals, but instead lattice distortions are observed in the a-b-plane. This phenomenon may indicate that both strain relaxation and charge modulation in the a-b-plane are important to the occurrence of superconductivity in the copper oxides.

In-plane X-ray scattering of epitaxial structures

A new approach for in-plane X-ray scattering from the cleavages of epitaxial films or superlattices, where the scattering vectors are parallel to the interfaces, is proposed. This method can be employed to determine directly the in-plane X-ray strains and other atomic registry along the interfaces of the epitaxial structures.