Chen Yanfeng

Raman spectroscopic study of ceramic Sr2Bi4Ti5O18

Raman spectra of ceramic Sr2Bi4Ti5O18 (SBTi5) are reported to consist of four different Raman bands. Temperature-dependent spectra reveal the relationship between the lattice vibration and the materials structure. There appears a relatively large change in structure of the material at about 273K. The anharmonic potential the material has a great influence on its phonon mode full width at half maximum (FWHM), which can be expressed by a function of temperature. Theoretical fittings of the FWHMs for the two modes around 312 cm−1 and 464 cm−1 indicate that the latter phonon mode is more anharmonic than the former one.

A Study of 90° Ferroelectric Domain Structures in PbTiO3 Thin Films by Means of Transmission Electron Microscopy

PbTiO3 thin films prepared by metalorganic chemical vapor deposition method were investigated using a transmission electron microscope. The as-deposited thin films were highly c-axis oriented, 90° a-c domains were observed and their crystallographic characteristics were investigated. Tetragonality of the PbTiO3 films was also obtained. The disappearance of 90° domains in the very thin film was found and attributed to surface relaxation effect.

Metamaterial based on elastic mechanics

In recent years, artificial metamaterials base on micro structures are showing huge development potential in fields of materials science, acoustics, seismology and information technologies, due to their devisable physical singularities which do not exist in natural materials. The study of metamaterial was born out of electromagnetic metamaterial. Nowadays, metamaterials have achieved a big leap forward with developments in the fields of acoustic, thermal, static, static magnetic and elastic mechanics, which greatly expand their study fields. With the help of a Milton graph, we focus on the extraordinary characteristics of novel elastic mechanics-based metamaterials and their species, such as acoustic metamaterials with negative mass density and elastic modulus, auxetic metamaterials with negative Poissons ratio, inverse bulging metamaterials with shear modulus G =0 and ultra-light materials with high strength. In addition, combining with the transform mechanical, this paper focuses on the propagation characteristics of acoustic and elastic waves in this elastic mechanics metamaterial and then elaborated the characteristics and physical effects of surface acoustic waves in the interface of metamaterials with negative elasticity parameters. Finally, we make a summary and prospect of the development of metamaterials combining with the elastic mechanics metamaterial research condition in China, such as metamaterial and acoustic metamaterial operating acoustic and elastic wave propagation using the elastic mechanics, design and development of a new type of elastic mechanics metamaterial. We hope this will help to accelerate the application of this metamaterial in many research fields.

An Empirical Formula Approach to Total Cross Sections for Electron Scattering on Polyatomic Molecules

Considering the real experimental process of e-molecule scattering a new empirical formula has been developed to calculate the total cross sections (TCSs) for electron scattering on polyatomic molecules (CH4, C2H2, CH3OH and CH3F). The present results are compared with other available theoretical results and experimental data. The new formula incorporates an energy factor f(E) to represent the elastic and inelastic changing process during experiments. It depends on no adjustable parameters and has also extended the validity of the empirical approaches to lower energy range further.