Obtaining Greatly Improved Dielectric Constant in BaTiO3-Epoxy Composites with Low Ceramic Volume Fraction by Enhancing the Connectivity of Ceramic Phase

First-Principles Study on Evolution of Magnetic Domain in Two-Dimensional BaTiO3 Ultrathin Film Doped with Co under Electric Field

The magnetization mechanism of Co-doped BaTiO3 ultrathin films is a subject of debate, which results in difficulties with the design of new multiferroics based on BaTiO3 matrixes. With the aid of a first-principles approach, it was observed that when the interstitial site and Ti vacancy were filled with Co, the configuration behaved in a nonmagnetic manner, indicating the significance of the Co content. Moreover, in the case of Co substituting two neighboring Ti atoms, when a direct current field was applied in the [100] direction, the magnetic domains excluding those in the [100], [010], and [001] directions were directed away. Further, the magnetoelectric constant was evaluated at ~449.3 mV/cmOe, showing strong magnetoelectric coupling at room temperature. Clearly, our study indicates that strict control of Ba, Ti, O, and Co stoichiometry can induce an electric and magnetic field conversion in two-dimensional BaTiO3 and may provide a new candidate for single-phase multiferroics for application in next-generation multifunctional devices.

Preparation of High-k Polymeric Composites Based on Low-k Boron Nitride Nanosheets with High-Connectivity Lamellar Structure

Typically, the basic method to enhance the dielectric response of polymer-based composites is to fill giant dielectric ceramic fillers, such as BaTiO₃ and CaCu₃Ti₄O₁₂, into the polymer matrix. Here, by using low-k boron nitride (BN) with well-controlled microstructure and surface, we successfully prepared a high-k polymeric composite, where the improvement in the dielectric constant of the composite even exceeds that of composites containing BaTiO₃ and CaCu₃Ti₄O₁₂ particles at the same weight percent. First, a lamellar boron nitride nanosheet (BNNS) aerogel was prepared by bidirectional freezing and freeze drying, respectively, and then the aerogel was calcined at 1000 °C to obtain the lamellar BNNS skeleton with some hydroxyl groups. Finally, the epoxy resin (EP) was vacuum impregnated into the BNNS skeleton and cured inside to prepare the lamellar-structured BNNSs/EP (LBE) composites. Interestingly, the dielectric constants of LBE with a 10 wt % BNNS content reached 8.5 at 10³ Hz, which was higher by 2.7 times than that of pure EP. The experimental data and the finite element simulations suggested that the increased dielectric constants of LBE resulted from the combination of two factors, namely, the lamellar microstructure and the hydroxyl groups. The stacking of the BNNS phase into a highly connected lamellar skeleton significantly increased the internal electric field and the polarization intensity, while the introduction of hydroxyl groups on the BNNS surface further improved the polarization of the composite, resulting in a significant increase in the dielectric constant of the LBE. This work provides a new strategy for improving the dielectric constant through the microstructure design of composites.

Nano-Sized Calcium Copper Titanate for the Fabrication of High Dielectric Constant Functional Ceramic-Polymer Composites

A novel calcium copper titanate (CaCu₃Ti₄O₁₂)–polyvinylidene fluoride composite (CCTO@PVDF) with Cu-deficiency was successfully prepared through the molten salt-assisted method. The morphology and structure of polymer composites uniformly incorporated with CCTO nanocrystals were characterized. At the same volume fraction, the CCTOs with Cu-deficiency displayed higher dielectric constants than those without post-treatment. A relatively high dielectric constant of 939 was obtained at 64% vol% CCTO@PVDF content, 78 times that of pure PVDF. The high dielectric constants of these composites were attributed to the homogeneous dispersion and interfacial polarization of the CCTO into the PVDF matrix. These composites also have prospective applications in high-frequency regions (10⁶ Hz). The enhancement of the dielectric constant was predicted in several theoretical models, among which the EMT and Yamada models agreed well with the experimental results, indicating the excellent distribution in the polymer matrix.

Parallel Structure Enhanced Polysilylaryl-enyne/Ca0.9La0.067TiO3 Composites with Ultra-High Dielectric Constant and Thermal Conductivity

With the rapid development of the microwave communication industry, microwave dielectric materials have been widely studied as the medium of signal transmission. Nowadays, with the increase in communication frequency, devices are miniaturized, and dielectric materials are required to have higher dielectric constants. At the same time, the miniaturization of devices brings about an increase in power density, which puts forward higher requirements for the thermal conductivity of materials. In this work, polysilylaryl-enyne (PSAE) and Ca_0.9La_0.067TiO₃ (CLT) were chosen as the matrix and filler, respectively, to construct a parallel model composite through a freeze casting method and a 0-3 model composite through the direct mixing method, respectively. After comparing the microstructures of the two models, their dielectric properties and thermal conductivity were measured and simulated. The parallel model composites in the stable range possess uniform parallel structures, and the solid content limit for them could be as high as 73.2%, which is much higher than that of the 0-3 model composites. While the 0-3 model composite possesses an optimal dielectric constant of 25.4 (@10 GHz) and a thermal conductivity of 0.965 W·m^-1·K^-1, the parallel model composite possesses a 2 times higher dielectric constant of 76.2 (@10 GHz) and a 1 times higher thermal conductivity of 2.095 W·m^-1·K^-1. Since the parallel model composite possesses much higher dielectric constant and thermal conductivity than traditional 0-3 model composites, it can be an excellent candidate for microwave communication.