Optical switching properties of RCo2-type alloy hydride based solid state device
TL;DR: In this article, the optical switching properties of a solid state device based on Ho0.6Mm0.4Co2 (HMC) alloy thin film as a switching active layer, water pretreated Nafion membrane as a solid electrolyte, and a transparent conducting indium tin oxide (ITO) as a counterelectrode are investigated.
Abstract: The optical switching properties of a solid state device based on Ho0.6Mm0.4Co2 (HMC) alloy thin film as a switching active layer, water pretreated Nafion membrane as a solid electrolyte, and a transparent conducting indium tin oxide (ITO) as a counterelectrode are investigated. The device is simple and has a reduced layer sequence of HMC/Pd/Nafion/ITO. The reversible optical switching of this device has been studied during electrochemical galvanostatic charging-discharging as well as cyclic voltammetric measurements. Further, the optical switching durability of the device has been tested by repeated electrochemical hydrogenation-dehydrogenation, and the variations in the optical switching properties are discussed. The special characteristic of the device is that it can reversibly switch between a metallic reflecting state and a semiconducting transparent state by a small reversible applied current/voltage indicating the potential substitution for conventional electrochromic devices.
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TL;DR: In this paper, the performance of selected polypyrrole/Nafion composite membranes is tested in a static vanadium redox cell and the results show that polyaniline and polypryrole interact differently with Nafion.
78 citations
TL;DR: In this paper, the propagation and transformation of electromagnetic waves through spatially homogeneous yet smoothly time-dependent media within the framework of classical electrodynamics is explored. But the authors do not consider the effect of the time-varying permittivity of the media.
Abstract: We explore the propagation and transformation of electromagnetic waves through spatially homogeneous yet smoothly time-dependent media within the framework of classical electrodynamics. By modelling the smooth transition, occurring during a finite period τ, as a phenomenologically realistic and sigmoidal change of the dielectric permittivity, an analytically exact solution to Maxwell׳s equations is derived for the electric displacement in terms of hypergeometric functions. Using this solution, we show the possibility of amplification and attenuation of waves and associate this with the decrease and increase of the time-dependent permittivity. We demonstrate, moreover, that such an energy exchange between waves and non-stationary media leads to the transformation (or conversion) of frequencies. Our results may pave the way towards controllable light–matter interaction in time-varying structures.
50 citations
Cites background from "Optical switching properties of RCo..."
...These mechanisms enable one to employ the optical switching of the refractive index for various purposes, such as quantum interference [20], information processing [21, 22, 23], material science [24, 25, 26], control of spontaneous emission [27], and several others [28, 29, 30, 31, 32, 33]....
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01 Jan 2012
TL;DR: In this paper, metal hydrides have been extensively studied for their hydrogen storage capacity, reversibility, kinetics and cyclic stability, and they find applications in Ni-MH (metal hydride) batteries, on-board energy supply, hydrogen isotope separation, gas purification, heat pumps, sensors and actuators.
Abstract: Hydrogen is a clean fuel as it produces only water as a by-product and there is no emission of pollutants or greenhouse gases. Storage of hydrogen is one of the main issues in exploiting it as an economical fuel. Several intermetallic compounds and alloys absorb and desorb hydrogen at moderate temperature and pressure. This class of materials, known as metal hydrides, are being extensively studied for their hydrogen storage capacity, reversibility, kinetics and cyclic stability. Metal hydrides find applications in Ni–MH (metal hydride) batteries, on-board energy supply, hydrogen isotope separation, gas purification, heat pumps, sensors and actuators. It is also of fundamental interest to study the interaction of hydrogen with various materials and the changes in their physico-chemical properties.
15 citations
TL;DR: Gremaud et al. as mentioned in this paper investigated the microstructure of Mg-Ti-H thin films and found that the formation enthalpy per Ti atom was lowered by up to 0.5
Abstract: Mg-Ti-H thin films exhibit interesting optical and electrical properties, offering a wide range of possible applications from coatings on solar collectors and smart windows to optical hydrogen sensors and semiconductor devices. However, Ti is known to be immiscible in Mg, and the microstructure of Mg-Ti thin films is not fully understood. In this work density functional theory calculations were used to investigate the ${\text{Mg}}_{100\ensuremath{-}y}{\text{Ti}}_{y}$ system with $1.56\ensuremath{\le}y\ensuremath{\le}98.44$. The crystal structure, mixing enthalpy, and electronic structure were compared for two different distributions of Ti: quasirandom and segregated. It was found that although the crystal structures did not differ significantly, the formation enthalpy per Ti atom was lowered by up to $\ensuremath{\sim}0.5\text{ }\text{eV}$ when Ti was arranged in nanoclusters. This gives support to previous experimental findings of chemical short-range order in Mg-Ti thin films [R. Gremaud et al., Phys. Rev. B 77, 144204 (2008)]. As a consequence of the decrease in the mixing enthalpy upon clustering the occurrence of short-range chemical order in all reported metastable Mg-Ti alloys with extended solubility is proposed. Further inquires into the influence of the size of the clusters revealed that the mixing enthalpy reaches a minimum after which further growth makes little difference, indicating that the phenomenon of nanoscale clustering must be understood separately from the larger scale phase separation occurring in an equilibrium process. The relaxed crystal structures were compared to experimental values from several sources and lattice-parameter variations as well as deviations from Vegard's law were discussed. Dependence of the size and shape of the nanoclusters on synthesis method is offered as an explanation for the large variation among the experimental lattice parameters. Local density of states calculations illustrated how segregated Ti forms a local environment resembling pure Ti while it was necessary to perform Bader analysis in order to obtain the correct picture of the charge transfer between Mg and Ti. Randomly distributed Ti atoms affect the charge distribution severely and the further the Ti atoms are apart the larger is the charge transfer from Mg. It was shown that a very limited amount of Ti nearest neighbors is sufficient for Ti to experience an imitation of elemental state, removing the driving force for further nucleation.
14 citations
Journal Article•
TL;DR: The optical appearance of yttrium thin film electrodes can be electrochemically switched from mirrorlike to highly transparent by making use of the hydride-forming properties of Y as discussed by the authors.
Abstract: The optical appearance of yttrium thin film electrodes can be electrochemically switched from mirrorlike to highly transparent by making use of the hydride-forming properties of Y. A strong alkaline solution is a suitable electrolytic environment for obtaining stable electrochromic electrodes. The presence of a thin Pd layer covering the Y electrode is essential in providing a sufficiently high electrocatalytic activity for the electrochemical charge-transfer reaction. Hydrogen is irreversibly bound in Y-dihydride and reversibly bound in Y-trihydride. The optical changes are reversible and are induced within a narrow hydrogen concentration range, making this typical electrode material interesting for application in a new type of electrochromic devices.
3 citations
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TL;DR: In this article, the diffusion constants of hydrogen in cubic (C15-type) Laves phase Ho 1 - x Mm x Co 2 (x = 0, 0.2 and 0.4, Mm = mischmetal ) alloys were measured in the α-phase (solid solution) region over the temperature range of 500 − 800 ∘ C using Sieverts-type apparatus.
3 citations
TL;DR: In this paper, electrical resistivity studies on mischmetal-substituted, C15 type AB2 alloy (Mm0.2Tb0.8Co2) hydrides with varied hydrogen interstitial concentrations have been carried out in the temperature range 80−300 K.
Abstract: Electrical resistivity studies on mischmetal-substituted, C15 type AB2 alloy (Mm0.2Tb0.8Co2) hydrides with varied hydrogen interstitial concentrations have been carried out in the temperature range 80−300 K. Hydrogen concentration-dependent metal-semiconductor-like transition has been observed and explained based on the charge transfer between hydrogen and the 3d band and the reduction in 6S component of the electron density. Polycrystalline thin film of the alloy capped with palladium has been obtained by electron beam evaporation technique on clean glass substrates. Switching properties from reflecting to a transparent state by electrochemical polarization in an alkaline electrolyte of pH 13 at room temperature have been investigated. In addition, the cyclic durability of the films has been studied and compared with that of rare-earth-based switchable mirror films. Preferential interstitial site occupancy for the hydrogen atoms has been analyzed based on the curent voltage characteristics of alloy thin ...
3 citations