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 paper, mixed rare earth oxides derived from bastnasite and monazite ores were purified with respect to non-rare-earth metallic impurities and the molecular weight of the misch metal was determined both directly and by calculation from the chemical composition.
Abstract: Mixed rare earth oxides derived from bastnasite and monazite ores were purified with respect to non-rare-earth metallic impurities. The purified oxide was first converted to the fluoride which was then reduced by calcium to the metal (misch metal). The various misch metals were analyzed for impurities and for the percentage of each rare earth element present. The molecular weight of the misch metal was determined both directly and by calculation from the chemical composition. The melting point, transition temperature and lattice parameters were determined for each batch of metal and compared with values calculated from the respective properties of the pure metals and the percentage of each metal present. The hardness is about the same as those found for the high purity individual metals, while the values of the resistance ratio R 300k R 4.2k were one or two orders of magnitude smaller than those reported for the individual pure metals.
20 citations
TL;DR: In this article, an all-solid-state switchable mirror was fabricated by magnetron sputtering, and a relationship between density and electrochemical properties of Ta 2 O 5 thin film was investigated to improve the optical switching property of the device.
Abstract: We have fabricated an all-solid-state switchable mirror as a type of smart window by magnetron sputtering. The multilayer structure of Mg4Ni/Pd/Ta 2 O 5 /WO 3 /indium tin oxide/glass is included in the device. Each material of Mg 4 Ni, Pd, Ta 2 O 5 , and WO 3 in the device plays optical switching, proton injector, solid electrolyte, and ion storage, respectively. A relationship between density and electrochemical property of Ta 2 O 5 thin film deposited by reactive dc magnetron sputtering was investigated to improve the optical switching property of the device. Ta 2 O 5 thin film with a density of 3.8 g/cm 3 had better electrochemical property than that with other densities. The transmittance at a wavelength of 670 nm of the device using Ta 2 O 5 thin film with a density of 3.8 g/cm 3 was reached from 0.1% (reflective state) to 46% (transparent state) within 20 s by applying voltage. We suggest that the optical switching property of the device was affected by the density of Ta 2 O 5 thin film.
17 citations
TL;DR: In this article, the structural properties of hydrogenated Ho1−xMmxCo2-hydrides were investigated using powder x-ray diffraction and the structural stability of these alloys upon repeated hydrogenation and dehydrogenation cycles was investigated.
Abstract: Thermodynamic and hydrogen-induced structural properties of hydrogenated Ho1−xMmxCo2 (x = 0, 0.1, 0.2, 0.3 and 0.4, Mm = mischmetal) alloys have been investigated. The hydrogen absorption pressure-composition isotherms were studied in the temperature range 50–200 °C and pressure range 0.001–1 bar using a Sieverts-type apparatus. The effect of Mm on the equilibrium plateau pressure and hydride stability has been discussed. Structural analyses and hydrogen-induced amorphization of Ho1−xMmxCo2hydrides were performed using powder x-ray diffraction. The structural stability of these alloys upon repeated hydrogenation and dehydrogenation cycles has been investigated. At lower hydriding pressure and temperatures, Ho1−xMmxCo2-hydrides retain their Laves C15 structure; however, the large lattice volume expansion about 24% is observed in the β-phase. The effect of hydrogenation pressure and temperature and Mm concentration on the hydrogen-induced transformation from crystalline Ho1−xMmxCo2-H to amorphous Ho1−xMmxCo2-H and recrystallization into elemental hydrides have been studied and discussed.
14 citations
TL;DR: In this article, the authors present the results on electrochemical behavior of the Y/Pd cathode and its reversible optical switching paying attention to some common problems that might affect the device work and even cause its destruction.
Abstract: A reversible optical transition in rare-earth metal hydrides can take place in a gas phase (when H 2 is injected into the chamber with rare-earth metal film and pumped out periodically) as well as in an electrolyte solution (when the electrode of active metal is polarised cathodically and depolarised). The liquid hydrogenation process, though more reliable from technological point of view, still presents some undesirable side effects and inferior longevity due to high reactivity of metals and their hydrides towards electrolyte solutions and enhanced corrosion. In this paper, we present our results on electrochemical behaviour of the Y/Pd cathode and its reversible optical switching paying attention to some common problems that might affect the device work and even cause its destruction. Based on these data, we have discussed a possible design and optimum operational conditions of the planar electrochemical cell: type of electrolyte used in the cell (liquid, solid or polymeric); role and design of the anodic electrode and the anodic process accomplished on it; sealing problems due to the necessity to obtain a hermetically closed cell with a liquid electrolyte inside and a possible gas evolution under the operation.
13 citations
TL;DR: The structural and electrical transport properties of Ho1−xMmxCo2 (x=0, 01, 02, 03, and 04 and Mm=mischmetal) alloys and their hydrides in the hydrogen concentration (y) range of 0⩽y ⩽36 have been determined through the powder x-ray diffraction (XRD) and temperature dependence of electrical resistivity [ρ(T)] measurements.
Abstract: The structural and electrical transport properties of Ho1−xMmxCo2 (x=0, 01, 02, 03, and 04 and Mm=mischmetal) alloys and their hydrides in the hydrogen concentration (y) range of 0⩽y⩽36 have been determined through the powder x-ray diffraction (XRD) and temperature dependence of electrical resistivity [ρ(T)] measurements At room temperature, these compounds crystallize in MgCu2-type (C15) structure The crystalline nature and lattice expansion of hydrogenated alloys have been studied using the hydrogen concentration dependence of XRD peak analysis indicating the coexistence of two hydride phases at intermediate hydrogen concentrations The temperature dependence of the electrical resistivity of alloys has been discussed based on the conduction electron scattering and spin fluctuation scattering mechanisms The changes in magnetic ordering and transition temperature upon Mm substitution and at different concentrations of hydrogen loadings have been discussed Furthermore, the transformation from meta
7 citations