High energy density of BaTiO3@TiO2 nanosheet/polymer composites via ping-pong-like electron area scattering and interface engineering

Dielectric substances exhibit great potential for high-power capacitors due to their high stability and fast charge–discharge; however, a long-term challenge is to enhance energy density. Here, we propose a poly(vinylidene fluoride) (PVDF) composite utilizing BaTiO3 nanoparticle@TiO2 nanosheet (BT@TO ns) 2D nanohybrids as fillers, aiming at combining the interfacial strategy of using a core–shell filler and the electron scattering of a 2D filler to improve the energy density. With 4 wt% filler, the composite possesses the largest breakdown strength (Eb) of 561.2 MV m−1, which is significantly enhanced from the 407.6 MV m−1 of PVDF, and permittivity of 12.6 at 1 kHz, which is a 23% increase from that of PVDF. A superhigh energy density of 21.3 J cm−3 with an efficiency of 61% is obtained at 550 MV m−1. The 2D BT@TO ns-filled composite exhibits a higher energy density than composites filled with core–shell 1D BT@TO nws or non-core–shell 0D BT, 1D TO, or 2D TO particles. The Eb and energy density improvements are attributed to the buffer layer-based interface engineering and enhanced area scattering of electrons caused by the 2D hybrids, an effect similar to that of a ping-pong paddle to scatter electric field-induced charge migrations in composites. Thus, an effective hybrid strategy is presented for achieving high-performance polymer composites that can be used in energy storage devices.

Late time cosmology in f(R,G)- gravity with interacting fluids

Cosmological models are obtained in a $f(R)$ modified gravity with a coupled Gauss-Bonnet (GB) terms in the gravitational action. The dynamical role of the GB terms is explored with a coupled dilaton field in two different cases (I) $f(R)= R + \gamma R^2- \lambda \left( \frac{R}{3m_s^2} \right)^{\delta}$ where $\gamma$, $\lambda$ and $\delta$ are arbitrary constants and (II) $f(R)=R$ and estimate the constraints on the model parameters. In the first case we choose GB terms coupled with a free scalar field in the presence of interacting fluid and in the second case GB terms coupled with scalar field in a self interacting potential to compare the observed universe. The evolutionary scenario of the universe is obtained adopting a numerical technique as the field equations are highly non-linear. Defining a new density parameter $\Omega_{H}$, a ratio of the dark energy density to the present energy density of the non-relativistic matter, we look for a late accelerating universe. The state finder parameters $\Omega_{H}$, deceleration parameter ($q$), jerk parameter ($j$) are plotted. It is noted that a non-singular universe with oscillating cosmological parameters for a given strength of interactions is admitted in Model-I. The gravitational coupling constant $\lambda$ is playing an important role. The Lagrangian density of $f(R)$ is found to dominate over the GB terms when oscillating phase of dark energy arises. In Model-II, we do not find oscillation of the cosmological parameters as the universe evolves. In the presence of interaction the energy from radiation sector of matter cannot flow to the other two sectors of fluid. The range of values of the strengths of interaction of the fluids are estimated for a stable universe assuming the primordial gravitational wave speed equal to unity.