Yttrium and lanthanum hydride films with switchable optical properties
TL;DR: In this article, thin films of yttrium and lanthanum with a layer of palladium through which hydrogen can diffuse are used to simulate metal-to-insulator transitions.
Abstract: IN many substances, changes in chemical composition, pressure or temperature can induce metal-to-insulator transitions1. Although dramatic changes in optical and electrical properties accompany such transitions, their interpretation is often complicated by attendant changes in crystallographic structure2. Yttrium, lanthanum and the trivalent rare-earth elements form hydrides that also exhibit metal–insulator transitions3–5, but the extreme reactivity and fragility of these materials hinder experimental studies5,6. To overcome these difficulties, we have coated thin films of yttrium and lanthanum with a layer of palladium through which hydrogen can diffuse. Real-time transitions from metallic (YH2 or LaH2) to semiconducting (YH3 or LaH3) behaviour occur in these films during continuous absorption of hydrogen, accompanied by pronounced changes in their optical properties. Although the timescale on which this transition occurs is at present rather slow (a few seconds), there appears to be considerable scope for improvement through the choice of rare-earth element and by adopting electrochemical means for driving the transition. In view of the spectacular changes in optical properties—yttrium hydride, for example, changes from a shiny mirror to a yellow, transparent window—metal hydrides might find important technological applications.
Citations
More filters
TL;DR: There are an immense number of sensors reported in the literature for hydrogen detection and in this article these sensors are classified into eight different operating principles, such as measuring range, sensitivity, selectivity and response time.
Abstract: Hydrogen sensors are of increasing importance in connection with the development and expanded use of hydrogen gas as an energy carrier and as a chemical reactant. There are an immense number of sensors reported in the literature for hydrogen detection and in this work these sensors are classified into eight different operating principles. Characteristic performance parameters of these sensor types, such as measuring range, sensitivity, selectivity and response time are reviewed and the latest technology developments are reported. Testing and validation of sensor performance are described in relation to standardisation and use in potentially explosive atmospheres so as to identify the requirements on hydrogen sensors for practical applications.
1,217 citations
TL;DR: In this review, the general field of electro Chromism is introduced, with coverage of the types, applications, and chemical classes of electrochromic materials and the experimental methods that are used in their study.
932 citations
TL;DR: In this article, the authors present a detailed review of the state-of-the-art for electrochromics and its applications in smart windows and provide ample references to current literature of particular relevance.
801 citations
TL;DR: In this article, the authors show that the hydrogen solubility of metal-hydrogen (M-H) systems is strongly affected by the morphology and microstructure of and the stress between regions of different hydrogen concentration.
Abstract: ▪ Abstract Metal-hydrogen (M-H) systems are interesting from both a theoretical and a practical point of view. M-H systems are utilized for energy-storage systems, in sensor applications, and in catalysis. These systems are often exploited as models for studying basic material properties, especially when the size of these systems is small and nonbulk-like contributions become dominant. Surfaces, nanocrystals, vacancy- and dislocation-rich materials, thin films, multilayers, and clusters as systems of major interest are addressed in this review. We show that the hydrogen solubility of M-H systems is strongly affected by the morphology and microstructure of and the stress between regions of different hydrogen concentration. For small-sized systems, surface- or interface-related sites become important and change the overall solubility as well as the phase boundaries of M-H systems. In thin films deposited on stiff substrates, compressive stresses evolve during hydrogen loading because the films are effective...
464 citations
TL;DR: In this paper, the fundamental physical and chemical properties of hydrogen and basic theories of hydrogen sorption reactions are described, followed by the emphasis on state-of-the-art hydrogen storage properties of selected interstitial metallic hydrides and magnesium hydride, especially for stationary energy storage related utilizations.
462 citations
References
More filters
TL;DR: A new theory is presented for describing band gaps and electronic structures of transition-metal compounds and both the metallic sulfides and insulating oxides and halides occur in a quite natural manner.
Abstract: A new theory is presented for describing band gaps and electronic structures of transition-metal compounds. A theoretical phase diagram is presented in which both the metallic sulfides and insulating oxides and halides occur in a quite natural manner.
2,190 citations
Book•
01 Jan 1995
TL;DR: In this paper, a case study on tungsten oxide is presented, where the authors discuss the preparation, structure, and composition of sputter-deposited tungstern oxide films.
Abstract: Part 1 Case study on tungsten oxide: bulk crystalline tungsten oxide tungsten oxide films - preparation, structure, and composition of evaporated films tungsten oxide films - preparation, structure, and composition of sputter-deposited films tungsten oxide films - preparation, structure, and composition of electrochemically and chemically prepared films tungsten oxide films - ion intercalation/deintercalation studied by electrochemical techniques tungsten oxide films - ion intercalation/deintercalation studied by physical techniques tungsten oxide films -ultraviolet absorption and semiconductor bandgap tungsten oxide films - optical properties in the luminous and near-infrared range tungsten oxide films - theoretical models for the optical properties tungsten oxide films - electrical properties. Part 2 Electrochromism among the oxides (except tungsten oxide): molybdenum oxide films miscellaneous tungsten- and molybdenum-oxide-containing films iridium oxide films titanium oxide films manganese oxide films vanadium dioxide films vanadium pentoxide films nickel oxide films cobalt oxide films niobium oxide films miscellaneous oxide films systematics for the electrochromism in transition metal oxides inorganic non-oxide electrochromic materials. Part 3 Electrochromic devices: transparent electrical conductors electrolytes and ion conductors ion storage materials - brief overview devices with liquid electrolytes devices with solid inorganic electrolytes and ion conductors devices with polymer electrolytes time-dependent device performance - a unified treatment.
1,903 citations
842 citations
01 Jan 1988
TL;DR: In this article, the most important diagnostics in this phase will undoubtedly be the neutron diagnostics, but other systems which are essential in unravelling the energy balance, such as the bolometers will retain a key iminence as will diagnostics determining impurity and instability behaviour, including the spectroscopic and X-ray systems.
Abstract: (Laboratorium für Festkörperphysik, ETH) stability and disruption behaviour provoked by the a heat source. The most important diagnostics in this phase will undoubtedly be the neutron diagnostics, but other systems which are essential in unravelling the energy balance, such as the bolometers will retain a key im portance as will diagnostics determining impurity and instability behaviour, such as the spectroscopic and X-ray systems. The wall diagnostics will be required to give in formation on the plasma wall and radiation damage behaviour in this phase. It would also be useful to have direct information on a particle energy transfer and containment but it is not clear at present that suitable diagnostic techniques can be developed to operate in the intense radiation field. Infor mation on the effectiveness of the a parti cle heating will however be obtained from the neutron measurements. The various systems giving spatially resolved informa tion on temperature and density profiles will be essential for detailed energy balance analysis.
509 citations
TL;DR: In this paper, the optical constants of V${\mathrm{O}}_{2} have been determined between 0.25 and 5 eV both below and above the semiconductor-metal transition temperature.
Abstract: The optical constants of V${\mathrm{O}}_{2}$ have been determined between 0.25 and 5 eV both below and above the semiconductor-metal transition temperature ${T}_{t}=340\ifmmode^\circ\else\textdegree\fi{}$K. Reflectivity and transmission spectra have been measured on both single crystals and than films. The reflectivity spectra of the bulk crystals were measured with E \ensuremath{\perp} ($c$ axis) in the tetragonal phase [or \ensuremath{\perp} ($a$ axis) in the monoclinic phase], and with E parallel to these axes. While there are some differences in magnitude between the dielectric constants obtained from thin-film and single-crystal measurements, the structural features are in good agreement. Below ${T}_{t}$ there are four prominent absorption peaks centered near photon energies of 0.85, 1.3, 2.8, and 3.6 eV. Above ${T}_{t}$, metallic free-carrier absorption is observed below 2.0 eV, but the same two absorption peaks near 3 and 4 eV are present. The energy location and polarization dependence of these two higher energy peaks can be related to similar absorption peaks in rutile, and are interpreted using the rutile band structure. The results are consistent with a picture in which filled bands arising primarily from oxygen $2p$ orbitals are separated by approximately 2.5 eV from partially filled bands arising primarily from vanadium $3d$ orbitals. Transitions from the filled $2p$ bands are responsible for the high-energy peaks in the optical absorption in both the high- and low-temperature phases. In the high-temperature metallic phase, there is evidence that there is overlap among the $3d$ bands such that at least two bands are partially occupied by the extra $d$ electron per vanadium ion. In the low-temperature semiconductor phase, a band gap of approximately 0.6 eV opens up within the $3d$ bands, separating two filled bands from higher-lying empty bands. The two absorption peaks at 0.85 and 1.3 eV are due to transitions from these two filled bands.
509 citations