Jiaqi Lin

Enhanced dielectric performance of amorphous calcium copper titanate/polyimide hybrid film

We report the preparation of amorphous CaCu3Ti4O12/polyimide (a-CCTO/PI) hybrid films for the first time. It was found that a relatively high dielectric permittivity, low loss and low conductivity were simultaneously achieved in the a-CCTO/PI films. Compared with the PI matrix and the CCTO/PI film with a 10 vol% concentration of CCTO, the dielectric permittivity of the a-CCTO/PI film with a 3 vol% concentration of a-CCTO increased by 29% and 16%, respectively. Interfacial polarization relaxation mainly determines the properties of a-CCTO/PI films, and this can guide the future preparation of ceramic–polymer composites. All the above-mentioned properties are beneficial for the use of a-CCTO/PI hybrid films in the electronics industry, for applications such as printed circuit boards (PCBs).

Significantly enhanced energy storage density for poly(vinylidene fluoride) composites by induced PDA-coated 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 nanofibers

In this study, high aspect ratio TiO2 nanofibers (TiO2 NFs), BaTiO3 nanofibers (BT NFs), CaCu3Ti4O12 nanofibers (CCTO NFs) and 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 nanofibers (BZT-BCT NFs) were prepared via an electrospinning technique. The nanofibers have been modified with polydopamine (PDA), which exhibited excellent dispersion and good compatibility with the polymer matrix. The effects of the structure and morphology of the fillers on the dielectric properties, leakage current density and energy densities of the composites have been also discussed systematically. On comparing the five different poly(vinylidene fluoride) (PVDF) composites, we discovered that the BZT-BCT NFs/PVDF composite displayed low loss, small leakage current and excellent storage performance. On this basis, BZT-BCT NFs/PVDF composites with different volume contents were also fabricated. It can be found that the 7 vol% BZT-BCT NFs/PVDF nanocomposite possessed an excellent dielectric constant (e ∼ 17.6 at 100 Hz). Nevertheless, the 3 vol% BZT-BCT NFs/PVDF nanocomposite demonstrated higher energy storage density (Ue ∼ 7.86 J cm−3) and greater efficiency (η ∼ 58%) at 310 kV mm−1. This study may provide a new direction to enhance the energy density of inorganic/PVDF composites.

Nano-KTN@Ag/PVDF composite films with high permittivity and low dielectric loss by introduction of designed KTN/Ag core/shell nanoparticles

A designed nano-KTN/Ag core/shell structure endows nano-KTN@Ag/PVDF composite films with excellent properties of remarkably enhanced dielectric permittivity, low loss tangent and flexibility. It has been found that the incorporation of KTN@Ag nanoparticles can increase the average crystallite size of the β phase in a polymer matrix, which elevates the polarization level of the polymer matrix and increases the dielectric permittivity of the nanocomposites. 25 vol% composites own a remarkably enhanced dielectric permittivity (er = 230) at 100 Hz, which is due to MWS polarization at the internal interface between nano-KTN@Ag and the PVDF matrix, the increased induced polarization of the nanoparticles and the “boundary layer capacitor effect”. The low loss tangent is achieved because of an enhanced polarization reverse speed by the Ag shells and a blockage of charge transfer by PVDF chains. The percolation threshold of the composite films (fc = 0.317) was predicted by the percolation theory, and the theoretical results were in good agreement with the experimental data.

Geometrical shape adjustment of KTa0.5Nb0.5O3 nanofillers for tailored dielectric properties of KTa0.5Nb0.5O3/PVDF composite

This paper indicates that rational design and precise control for the structure and shape of nanofillers are effective for achieving the desired permittivity and breakdown strength for high energy densities of polymer nanocomposites. Two types of KTa0.5Nb0.5O3 (KTN) nanoparticles with different shapes (NC-KTN and NR-KTN) were introduced into the PVDF matrix. The molecular dynamic simulation and the Brunauer–Emmett–Teller (BET) surface area proved that the nonbonding interaction energy is stronger in the NR-KTN/PVDF composite films due to the larger surface area of NR-KTN (30.96 m2 g−1). In addition, the interfacial polarization related to the shape of nanofillers further improved the dielectric permittivity of NR-KTN/PVDF composite films. Through the comparison between the experimental data and various theoretical models, we concluded that the geometric shape of fillers has a significant impact on the dielectric constant of composite films.

The effect of oxygen vacancy on structures and optical properties of the lead-free Ba0.5Sr0.5TiO3 by first-principles calculation

The structural and optical properties of lead-free Barium strontium titanate Ba0.5Sr0.5TiO3 with oxygen vacancies (BST-O) were investigated by first-principles calculations of density functional theory. The results show that the O vacancy has significant influence on the electronic structure and optical performance of the materials. The structures generate a phase transition from cubic to tetragonal phase, when an O atom has removed from the pure Ba0.5Sr0.5TiO3 (BST). The electron density conformation is distributed, which induce conspicuous distortion of the oxygen octahedron. The calculated optical properties, complex dielectric function, refractive index, absorption coefficient, show that the absorption spectra of the BST-O have multimodality and smaller amplitude by comparing with ideal BST. And the oxygen vacancy lead the increase of refractive index and the decrease of absorption coefficient in visible light frequency region (1.59~3.11 eV), the optical anisotropism is also found in the BST-O. Introduction Barium strontium titanate is one of the well known perovskite materials with its excellent ferroelectric and dielectric performance, which is considered as a candidate to replace lead based materials due to the environment issue. Its desirable high dielectric constant, low dielectric losses, strong remnant polarization and low current leakage has been attractive for its fundamental research, and the material could be used for various applications such as dynamic random, access memory, ceramic capacitors, pyroelectric sensors, infrared detectors, chemical sensor, biosensor, microwave devices and optoelectronic applications in recent years . With the intensive study on BST material, a large quantity of tentative exploration on ceramic, film, composite and doping vario-property of BST have been completed . However, most of the experiments of BST focused on the properties in electrical and microwave frequency . The optical response of BST is not very clear. The first principle method is an effective and efficient method for material research, which is applied to the study of perovskite type materials in the last decades . Many typical perovskite materials were studied by this method, such as tantalum niobate (KTN), strontium titanate (SrTiO3) and lead zirconate titanate (PZT) , which has succeed in predicting electronic properties, band structure and optical properties of perovskite materials. The related properties of ideal BST are also investigated though first principle method, but defect state of BST is scarcely researched [12, . As is well known, the oxygen defects are unavoidable during experimental process, F. M. Pontes et al verified that the postannealing temperature and oxygen atmosphere have important influence on the dielectric properties of BST . In this paper, the possible defects in the process of the experiment were considered. The two models of the ideal bulk of BST and BST with O vacancy were designed and the effect of oxygen vacancy on structures and optical properties of the lead-free Ba0.5Sr0.5TiO3 were investigated by first-principles in detail. 5th International Conference on Information Engineering for Mechanics and Materials (ICIMM 2015)