Electronic polarization and charge transfer effects play a crucial role in thermodynamic, structural and transport properties of room-temperature ionic liquids (RTILs). These non-additive interactions constitute a useful tool for tuning physical chemical behavior of RTILs. Polarization and charge transfer generally decay as temperature increases, although their presence should be expected over an entire condensed state temperature range. For the first time, we use three popular pyridinium-based RTILs to investigate temperature dependence of electronic polarization in RTILs. Atom-centered density matrix propagation molecular dynamics, supplemented by a weak coupling to an external bath, is used to simulate the temperature impact on system properties. We show that, quite surprisingly, non-additivity in the cation-anion interactions changes negligibly between 300 and 900 K, while the average dipole moment increases due to thermal fluctuations of geometries. Our results contribute to the fundamental understanding of electronic effects in the condensed phase of ionic systems and foster progress in physical chemistry and engineering.
Mesoporous silica matrices have been prepared via classic acid catalyzed and sono-catalyzed sol-gel routes. Tetramethoxysilan (TMOS) and methyl-trimethoxysilane (MTMS) were used as silica precursors, and N-butyl-3-methylpyridinium tetrafluoroborate ([bmPy][BF4]) was employed as co-solvent and pore template. The ionic liquid (IL) to silica mole ratio was varied between 0.007 and 0.07. Nitrogen adsorption-desorption and small-angle neutron scattering measurements were used to characterize the obtained materials. The ionic liquid played the role of catalyst that affected the formation of the prim…
Based on classical molecular dynamics simulations, we discuss the impact of Coulombic interactions on a comprehensive set of properties of room temperature ionic liquids (RTILs) containing 1,3 dimethylimidazolium (MMIM+), N butylpyridinium (BPY+), and bis(trifluoromethane sulfonyl)imide (TFSI-) ions. Ionic transport is found to be noticeably hindered by the excessive Coulombic energy, originating from the neglect of electronic polarization in the condensed phase of these RTILs. Starting from the models, recently suggested by Lopes and Padua, we show that realistic ionic dynamics can be achieve…
Perovskites have proven to be a promising candidate for highly-efficient solar cells, light-emitting diodes, and X-ray detectors, overcoming limitations of inorganic semiconductors. However, they are notoriously unstable. The main reason for this instability is the migration of mobile ions through the device during operation, as they are mixed ionic-electronic conductors. Here we show how measuring the capacitance in both the frequency and the time domain can be used to study ionic dynamics within perovskite-based devices, quantifying activation energy, diffusion coefficient, sign of charge, c…
Based on the different covalent versus ionic chemical bonding and isoelectronic rutile CrO2, CrNF is proposed starting from ordered rutile derivative structures subjected to full geometry optimizations. The ground state structure defined from cohesive energies is of MgUO4-type, characterized by short covalent Cr-N and long ionic Cr-F distances. Like CrO2 it is a half-metallic ferromagnet with M = 2 Bohr Magnetons integer magnetization per formula unit with reduced band gap at minority spins. Major differences of magnetic response to pressure characterize CrNF as a soft ferromagnet versus hard …
In situ electrochemical dilatometry was used to study, for the first time, the expansion behavior of a porous carbon electrode in a pure ionic liquid, 1-ethyl-3-methyl-imidazolium-tetrafluoroborate. For a single electrode, an applied potential of -2 V and +2 V against the potential of zero charge resulted in maximum strain of 1.8 % and 0.5 %, respectively. During cyclic voltammetry, the characteristic expansion behavior strongly depends on the scan rate, with increased scan rates leading to a decrease of the expansion. Chronoamperometry was used to determine the equilibrium specific capacitanc…
Molecular dynamics calculations are carried out on pure, Al-substituted, and In-substituted LLZO. The calculations show that the tendency of Al to occupy the 24d sites in LLZO lithium ion conductors is hypothesized here to negatively impact ionic conductivity. The room-temperature ionic conductivity of In-LLZO, in which the In resides at the 48g sites, is predicted to be an order of magnitude higher than Al-LLZO. Consideration of the simple tetrahedral topology of the lithium ion conduction network suggests that the increased conductivity arises because the 48g site sits at a bridge in the lit…
Nowadays ferromagnetism is often found in potential diluted magnetic semiconductor systems. However, many authors argue that the observed ferromagnetism stems from ferromagnetic precipitates or spinodal decomposition rather than from carrier mediated magnetic impurities, as required for a diluted magnetic semiconductor. In the present paper we answer this question for Fe-implanted ZnO single crystals comprehensively. Different implantation fluences and temperatures and post-implantation annealing temperatures have been chosen in order to evaluate the structural and magnetic properties over a w…
Electrical charging of parallel plates confining a model ionic liquid down to nanoscale distances yields a variety of charge-induced changes in the structural features of the confined film. That includes even-odd switching of the structural layering and charging-induced solidification and melting, with important changes of local ordering between and within layers, and of squeezout behavior. By means of molecular dynamics simulations, we explore this variety of phenomena in the simplest charged Lennard-Jones coarse-grained model including or excluding the effect a neutral tail giving an anisotr…
Ab intio calculations were done to investigate the structural, elastic, electronic and optical properties of the Cd-containing theoretically predicted MAX phase, Ti2CdN, in comparison with the isostructural and already synthesized phase, Ti2CdC. These calculations reveal that the substitution of C by N affects the lattice parameter c, whereas the lattice parameter a, remains almost unchanged. All the elastic constants and moduli increase when carbon is replaced by nitrogen. The elastic anisotropy in Ti2CdC is higher in comparison with that of Ti2CdN. Both these nanolaminates are brittle in nat…
Based on geometry optimization and magnetic structure investigations within density functional theory, unique uranium nitride fluoride UNF, isoelectronic with UO2, is shown to present peculiar differentiated physical properties. Such specificities versus the oxide are related with the mixed anionic sublattices and the layered-like tetragonal structure characterized by covalent like [U2N2]2+motifs interlayered by ionic like [F2]2- ones and illustrated herein with electron localization function graphs. Particularly the ionocovalent chemical picture shows, based on overlap population analyses, st…
The electrical transport properties of ultrathin YBCO films have been modified using an electric double layer transistor configuration employing an ionic liquid. The films were grown on SrTiO3 substrates using high pressure oxygen sputtering. A clear evolution from superconductor to insulator was observed in nominally 7 unit cell thick films. Using a finite size scaling analysis, curves of resistance versus temperature, R(T), over the temperature range from 6K to 22K were found to collapse onto a single scaling function, which suggests the the presence of a quantum critical point. However the …
Influence of BaTiO_3 nanoparticles on the anisotropy of the dielectric properties of nematic liquid crystal 5CB
Institute of Physics of the National Academy of Sciences of Ukraine（乌克兰国家科学院物理研究所）；Frantsevich Institute of Materials Science, the National Academy of Sciences of Ukraine（乌克兰国家科学院弗兰采维奇材料科学研究所）
