We study the kinetics of phase transitions in a Rayleigh-Benard system after onset of convection using 2D Swift-Hohenberg equation. An initially uniform state evolves to one whose ground state is spatially periodic. We confirmed previous results which showed that dynamical scaling occurs at medium quench (ǫ = 0.25) with scaling exponents 1/5 and 1/4 under zero noise and finite noise respectively. We find logarithmic scaling behavior for a deep quench (ǫ = 0.75) at zero noise. A simple method is devised to measure the proxy of domain wall length. We find that the energy and domain wall length exhibit scaling behavior with the same exponent. For ǫ = 0.25, the scaling exponents are 1/4 and 0.3 at zero and finite noise respectively.

Tunneling-induced negative permittivity is attributed to the low frequency plasmonic state in tunneling networks, where nickel nanoparticles are still isolated geometrically but connected electrically.

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The flexible metacomposites with tunable negative permittivity have great potential in wearable cloaks, stretchable sensors, and thin-film capacitors, etc. In this paper, the flexible graphene/polydimethyl­siloxane (GR/PDMS) metacomposites with tunable negative permittivity were prepared by an in situ polymerization method. The ac conductivity behavior, dielectric property, and impedance performance of the resulting composites with different graphene mass ratios (0–4 wt %) were studied. With the increase of graphene, the conductive mechanism of the resulting composites changed from hopping conduction to electron conduction, along with the change of microstructure. When graphene content in the composites came up to 3 wt %, the negative permittivity conforming to Drude model was observed. Further investigation revealed that there is a corresponding relationship between the permittivity and the reactance. It is demonstrated that the inductive character is responsible for the negative permittivity, while the capacitive character results in the positive permittivity.

We present a consistent interatomic force field for indium sesquioxide (In 2 O 3 ) and tin dioxide (SnO 2 ) that has been derived to reproduce lattice energies and, consequently, the oxygen vacancy formation energies in the respective binary compounds. The new model predicts the dominance of Frenkel-type disorder in SnO 2 and In 2 O 3 , in good agreement with ab initio defect calculations. The model is extended to include free electron and hole polarons, which compete with charged point defects to maintain charge neutrality in a defective crystal. The stability of electrons and instability of holes with respect to point defect formation rationalises the efficacy of n-type doping in tin doped indium oxide (ITO), a widely employed transparent conducting oxide in optoelectronic applications. We investigate the clustering of Sn substitutional and oxygen interstitial sites in ITO, finding that the dopants substitute preferentially on the cation crystallographic d site in the bixbyite unit cell, in agreement with experiment.The force field described here provides a useful avenue for the investigation of the defect properties of extended transparent conducting oxide systems, including solid solutions.

Polarizable shell-model potentials are widely used for atomic-scale modeling of charged defects in solids using the Mott–Littleton approach and hybrid Quantum Mechanical/Molecular Mechanical (QM/MM) embedded-cluster techniques. However, at the pure MM level of theory, the calculated defect energetics may not satisfy the requirement of quantitative predictions and are limited to only certain charged states. Here, we proposed a novel interatomic potential development scheme that unifies the predictions of all relevant charged defects in CeO2 based on the Mott–Littleton approach and QM/MM electronic-structure calculations. The predicted formation energies of oxygen vacancies accompanied by different excess electron localization patterns at the MM level of theory reach the accuracy of density functional theory (DFT) calculations using hybrid functionals. The new potential also accurately reproduces a wide range of physical properties of CeO2, showing excellent agreement with experimental and other computational studies. These findings provide opportunities for accurate large-scale modeling of the partial reduction and nonstoichiometry in CeO2, as well as a prototype for developing robust interatomic potentials for other defective crystals.

We investigate the use of renormalisation group methods to solve partial differential equations (PDEs) numerically. Our approach focuses on coarse-graining the underlying continuum process as opposed to the conventional numerical analysis method of sampling it. We calculate exactly the coarse-grained or 'perfect' Laplacian operator and investigate the numerical effectiveness of the technique on a series of 1 + 1-dimensional PDEs with varying levels of smoothness in the dynamics: the diffusion equation, the time-dependent Ginzburg-Landau equation, the Swift-Hohenberg equation and the damped Kuramoto-Sivashinsky equation. We find that the renormalisation group is superior to conventional sampling-based discretisations in representing faithfully the dynamics with a large grid spacing, introducing no detectable lattice artifacts as long as there is a natural ultra-violet cut off in the problem. We discuss limitations and open problems of this approach.

In this paper, the tunable negative permittivity and permeability of copper/yttrium iron garnet (Cu/YIG) composites, which were prepared by in situ synthesis process, were investigated in the radio frequency regime.