A. Rougier

Characterization of pulsed laser deposited WO3 thin films for electrochromic devices

Abstract Thin films of tungsten oxide were deposited on SnO2:F coated glass using pulsed laser deposition. The structure, morphology, composition of the films and thus the electrochromic properties are strongly dependent on the conditions of deposition. Emphasis is being made on both the influence of the oxygen pressure and the temperature of deposition. Crystallized films are obtained when deposited at 400°C with an oxygen pressure of 10−1 mbar while an oxygen pressure of 10−2 mbar leads to amorphous films whatever the substrate temperature is. For the lower oxygen pressure, blue colored and conductive films are deposited whereas colorless insulator films are obtained for an oxygen pressure of 10−1 mbar at room temperature (RT). The estimated optical band gaps for the films were found to be 3.2 eV when deposited at RT and 2.8 eV when deposited on a 400°C substrate while having an oxygen pressure of 10−1 mbar. Using Raman spectroscopy, the decrease of the optical band gap was ascribed to a decrease of the WO/O–W–O ratio correlated to an increase of the cluster size of tungsten oxide with crystallinity. By IR spectroscopy, we were able to relate the better electrochromic properties of the colorless films deposited at RT in an oxygen pressure of 10−1 mbar, to the presence of water.

Characterization of indium zinc oxide thin films prepared by pulsed laser deposition using a Zn3In2O6 target

Abstract Using a Zn 3 In 2 O 6 target, indium-zinc oxide films were prepared by pulsed laser deposition. The influence of the substrate deposition temperature and the oxygen pressure on the structure, optical and electrical properties were studied. Crystalline films are obtained for substrate temperatures above 200°C. At the optimum substrate deposition temperature of 500°C and the optimum oxygen pressure of 10 −3 mbar, both conditions that indeed lead to the highest conductivity, Zn 3 In 2 O 6 films exhibit a transparency of 85% in the visible region and a conductivity of 1000 S/cm. Depositions carried out in oxygen and reducing gas, 93% Ar/7% H 2 , result in large discrepancies between the target stoichiometry and the film composition. The Zn/In (at.%) ratio of 1.5 is only preserved for oxygen pressures of 10 −2 –10 −3 mbar and a 93% Ar/7% H 2 pressure of 10 −2 mbar. The optical properties are basically not affected by the type of atmosphere used during the film deposition, unlike the conductivity which significantly increases from 80 to 1400 S/cm for a film deposited in 10 −2 mbar of O 2 and in 93% Ar/7% H 2 , respectively.

Nickel oxide sol–gel films from nickel diacetate for electrochromic applications

Abstract Nickel diacetate tetrahydrate, [Ni(acetate)2·4H2O] and nickel diacetate dimethylaminoethanol, [Ni(acetate)2(dmaeH)2] were successfully used to deposit NiOx thin films on conductive glass substrates by sol–gel techniques for large area electrochromic applications. Homogeneous one layer films 100 nm thick were deposited by spin coating 0.5 M [Ni(acetate)2·4H2O] in dmaeH at 1000 rpm and by dip coating methods. The NiOx films were characterised by X-ray diffraction, transmission electron microscopy and atomic force microscopy. The thin film electrochromic performances were characterised by means of optical (transmittance) and electrochemical (cyclic voltammetry) methods. On early cycling NiOx thin films present an activation period, related to an increase in capacity. The electro-optical data show an increase in the electrochromic response (i.e. an increase in contrast and colouration efficiency) upon cycling. Following this initial activation period a steady state is reached in which the thin films reversibly switch from transparent to brown. The anodically coloured NiOx thin films are therefore suitable for use in a complete electrochromic cell with tungsten oxide as the cathodic colouring layer. However, the films are not fully stable with long cycling.

Electrochemically Inactive Nickel Oxide as Electrochromic Material

Nickel oxide thin films, known as optically active counter electrodes in electrochromic devices, were grown at room temperature under an oxygen pressure of 10 -1 mbar, using pulsed laser deposition (PLD). The influence of the film thickness, potential window, and extended cycling on the electrochromic properties was studied by means of complementary electrochemical, X-ray diffraction, and electron microscopy techniques. Independently of the substrate nature, transparent as-deposited films were crystallized with a [111] preferred orientation. The reversible color change from transparent to brownish is ascribed to a faradic process, involving the Ni 3+ /Ni 2+ redox couple, the intensity of which is enhanced with decreasing film thickness. Finally, taking into account a first chemical reaction when NiO thin films are immersed in KOH, a mechanism based on hydroxide electrochemically active phases is proposed for the electrochromic properties of PLD NiO thin films.

Mechanochemical synthesis of Li–Mn–O spinels: positive electrode for lithium batteries

Li-Mn-O oxides were synthesized by mechanochemistry from a stoichiometric mixture of Li 2 O and MnO 2 using various grinding times (0 < t milling < 15 h). X-ray diffraction patterns of the ground samples (t milling < 10 h) exhibit the same features as LiMn 2 O 4 spinel structure (SG: Fd3m) with, however, a slight discrepancy in the lattice parameter (a cub ) suggesting a non-stoichiometry of the Li-Mn-O oxides, a cub increases with milling time to reach for 8 h of grinding a value of 8.24 A similar to stoichiometric LiMn 2 O 4 . As a matter of fact, after 8 h of milling, mechanosynthesized Li-Mn-O spinel-type oxide shows quasi-identical electrochemical performances as high temperature LiMn 2 O 4 ground for 1 h.

Pulsed Laser-Deposited nickel oxide thin films as electrochromic anodic materials

Abstract Nickel oxide thin films were deposited on SnO2:F-coated glass using pulsed laser deposition. The influence of the oxygen pressure and the substrate temperature on the structure, morphology and electrochromic performances of NiOx thin films were investigated. Whatever the oxygen pressure (P O 2 ≤10 −1 mbar ) and substrate temperature ( RT ≤T s ≤300 ° C ) NiOx films were crystallized and exhibited a non-stoichiometry (x

Systematic study and performance optimization of transparent conducting indium–zinc oxides thin films

To optimize the physical properties of In 2 O 3 -ZnO pulsed laser deposited thin films, we embarked on a systematic study of their microstructural characterization and transport properties. We found that the electrical properties of the films are greatly governed by their microstructure, which evolves from granular to fiber and to columnar textures, as we go from cubic In 2 O 3 to hexagonal ZnO via Zn k In 2 O k+3 layered structure in the binary In 2 O 3 ZnO phase diagram. Maximum conductivity is reached for a Zn/(Zn + In) = 0.5 (at.) composition having a layered Zn k In 2 O k+3 - type structure with essentially k = 2, which was synthesized for the first time. Electrochemical measurements show that this film can be used as a transparent electrode in electrochromic devices operating either in an aqueous or organic medium.

A comparison of the extended x-ray absorption fine structure of nanocrystalline ZrO2 prepared by high-energy ball milling and other methods

We report the results of an extended x-ray absorption fine structure (EXAFS) study of a sample of ZrO2 prepared by high-energy ball milling. X-ray diffraction showed that the sample contained nanocrystals that were predominantly monoclinic with a particle size of 15 nm. The EXAFS for the sample was strongly attenuated in comparison to that for bulk monoclinic ZrO2. This has been interpreted as the ball-milled sample containing a large level of disorder whose possible origins are discussed. In contrast, our previous EXAFS studies of nanocrystalline oxides prepared by sol–gel methods have shown that these samples contain well-ordered crystallites with grain boundaries similar to those in bulk materials. It is concluded that ball-milled samples are very different from oxide nanocrystals produced by other techniques.

Synthesis, Structure, Lattice Dynamics and Electrochemistry of Lithiated Manganese Spinel, LiMn2O4

We report synthesis, crystal structure, lattice dynamics, and electrochemical features of the lithiated manganese oxide spinel prepared through solid state reaction by careful selection of precursors and synthesis conditions. Elemental analysis shows that the material is a lithium-rich spinel phase. X-ray diffraction data and Rietveld refinement indicate formation of a single phase, impurity free, normal spinel of LiMn 2 O 4 . Lattice dynamics have been investigated by vibrational spectroscopy and group theoretical analysis has been carried out. Electrochemical performances of the lithiated spinel manganese oxide have been investigated, and the voltage profile of the cathode during lithium intercalation-deintercalation processes, close to equilibrium, has been obtained. The upper 4-volt plateau provides over 130 mA h/g with an excellent cyclability.

Synthesis and crystal structures of dimethylaminoethanol adducts of Ni(II) acetate and Ni(II) acetylacetonate. Precursors for the sol–gel deposition of electrochromic nickel oxide thin films

The reaction between N,N-dimethylaminoethanol (dmaeH) and nickel(II) acetylacetonate, [Ni(acac)2]3 or Ni(II) acetate tetrahydrate, [Ni(CH3CO2)2(H2O)4] yields the new complexes [Ni(acac)2(dmaeH)] (1) and [Ni(CH3CO2)2(dmaeH)2] (2). Complexes (1) and (2) are mononuclear, containing six-coordinate Ni(II) atoms in slightly distorted octahedral environments. Complex (1) contains two bidentate and chelating acetylacetonate groups with a chelating dmaeH ligand. Complex (2) contains two monodentate acetate groups in a cis configuration and two chelating dmaeH ligands. Both complexes dissolve readily in dmaeH to form stable solutions, and are good precursors for the deposition of NiO thin films by sol–gel techniques. (1) and (2) were successfully used to grow electrochromic NiO thin films on conductive glass substrates. The surface morphology of the films was characterised by scanning electron microscopy (SEM) and atom force microscopy (AFM). The thin film performances were characterised by means of optical (transmittance) and electrochemical (cyclic voltammetry) methods. Upon cycling, the NiO thin films switch from brown to transparent in a reversible way exhibiting anodic electrochromic performance.