Analysis of the surface condition of Ti4Fe2Ox

The surface conditions of powder compounds Ti₄Fe₂O_x (x = 0.5; 1.0) have been studied by means of the XPS method. As in the case of the alloys, Ti_1.1 Fe, Ti_1.1Fe_0.9Mn_0.1 and Ti_1.1Fe_0.8Cu_0.1Ni_0.1 studied earlier the peculiarities of the XPS O 1s core-level spectra in Ti₄Fe₂O_x are also observed. The peculiarities can be connected with oxygen-containing gas molecules chemisorbed on the alloy surfaces. The dependence of activation temperature upon the type of oxygen-containing structures absorbed on the alloy surfaces has been established. A physical model of the activation process for TiFe-based alloys is proposed. In this model, the surface oxides play an active role in distinction from the segregation model where the oxides play a passive role.     

Color change of V2O5 thin films upon exposure to organic vapors

The reaction of amorphous V₂O₅ thin films with various organic vapors is investigated using in-situ optical transmission and in-situ Raman spectroscopic measurements. When V₂O₅ thin films are exposed to vapors of methanol, ethanol, acetone, and isopropanol, changes in the Raman spectrum are observed. These changes are similar to those due to alkali ion intercalation and most pronounced for methanol and ethanol. The optical transmission also increases when the thin films are exposed to methanol and ethanol vapors. Depositing a thin catalyst layer of palladium does not promote the reaction. This result has implications for using this material in hydrogen sensor applications, as extended exposure to organic vapors may not be differentiated from the presence of hydrogen.     

Study of electron-beam evaporated Sn-doped In2O3 films

Electron beam evaporated Sn-doped In₂O₃ films have been prepared from the starting material with composition of (1 − x) In₂O₃ − -x SnO₂, where x = 0.0, 0.010, 0.025, 0.050, 0.090, and 0.120. X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and X-ray diffraction analysis were carried out on the films. Luminous transmittance and electrical resistivity of the films, show weak dependence on x. The composition of the film ([Sn]/[In] atomic ratio) was found to differ from that of the starting material. In fact, the atomic ratio was higher in the film than in the starting material by a factor which increases with x (ranging from 1.0 to 2.6). There is a relatively broad resistivity minimum in the layer atomic ratio range Sn/In = 0.06 − -0.09. These results compare well with those reported in the literature for Sn-doped In₂O₃ films, prepared by pyrolitic (spray) method.     

Significant changes in phase-transition hysteresis for Ti-doped VO2 films prepared by polymer-assisted deposition

This study is one of a series of researches on polymer-assisted deposition (PAD) of thermochromic VO₂ film. This paper describes the synthesis of Ti-doped VO₂ films (V_1−xTi_xO₂, x=0-0.167) and a systematic investigation of the effects of Ti doping on morphology, crystalline phase and optical properties (visible transmittance, transmittance changes in near infrared (NIR) light across the metal-insulator transition (MIT), absorption edge, MIT temperatures and sharpness) of V_1−xTi_xO₂ films. The films showed excellent visible transmittance and large changes (∼50% at 2000 nm) in the NIR-light transmittance before and after MIT for samples with a wide range of Ti contents (0-10%). The width of the hysteresis loop was severely reduced, which is in agreement with a qualitative analysis using the nucleation theory, while the MIT sharpness was not obviously influenced. An increase in the MIT temperature was observed for all samples with Ti doping, in particular 18.5 °C for 2% Ti doping, which is quite large compared with those in the literature. However, the MIT seemed saturated at around 80 °C. The morphology evolution of Ti-doped VO₂ films was investigated for the first time. Interestingly, Ti doping could remarkably reduce the particle size of VO₂ films due to Ti enhanced heterogeneous nucleation process of VO₂ particles, indicating a new method for the growth of nanostructured VO₂ films.     

Effect of the organic–inorganic template ICS-PPG on sol–gel deposited V2O5 electrochromic thin film

We produced V₂O₅ thin films with sol–gel technique, using in the synthesis as a template agent, the so-called ICS-PPG. We studied the electrochromic behaviour of thin films with electrochemical techniques as slow scan cyclic voltammetry and cyclic voltammetry (SSCV, CV), impedance spectroscopy (EIS) and potentiostatic intermittent titration (PITT). Moreover, we measured transmittance spectra, optical bandgap of the material and, with the help of transmission electron microscopy (TEM), we found out informations about films structure. The addition of ICS-PPG produces more transparent samples in comparison with samples prepared without template agent. The ion storage capacity is only slightly increased and, with ageing, some deposits appear on the surface limiting the electrochemical performances.     

Effect of TiO2 mixtures on the optical, structural and electrochromic properties of Nb2O5 thin films

Metal oxide films are important for various optical devices and especially for solar energy materials. TiO₂-mixed Nb₂O₅ thin films have been produced by sol–gel dip-coating method. Several parameters such as heat treatment, thickness, and mixture percentages are studied for the effect of the optical, structural and electrochromic properties of the materials. Optical parameters of the films were calculated through transmission and reflection measurement by a refractive index, extinction coefficient and thickness analyzer. Structural, electrochromic and surface analyses of the films were done by X-ray diffractometer, potentiostat/galvanostat and atomic force microscope systems.     

Kinetics and thermodynamic behavior of WO3 and WO3:P thin films

 There is a considerable interest in the research and development of materials and devices, that can be used for optical switching of large-scale glazings. Several potential switching technologies are available for glazings, including those based on electrochromic, thermochromic and photochromic phenomena. One of the most promising technologies for optical switching devices is electrochromism (EC). In order to improve the electrochromic properties of tungsten oxide, we have investigated the effect of phosphorous insertion on the electrochromic behavior of oxide films prepared by the sol–gel process.The kinetics and thermodynamics of electrochemical intercalation of lithium into Li_xWO₃ and Li_xWO₃:P films prepared by the sol–gel process were investigated. The standard Gibbs energy for lithium intercalation was calculated. The chemical diffusion coefficients, D, of lithium intercalation into oxide, were measured by galvanostatic intermittent titration technique (GITT), as functions of the depth of lithium intercalation.     

Advanced electrochemical performance of Li4Ti4.95V0.05O12 as a reversible anode material down to 0 V

Li₄Ti_4.95V_0.05O₁₂ and Li₄Ti₅O₁₂ powders were successfully prepared by a solid-state method. XRD reveals that both samples have high phase purity. Raman spectroscopy indicates that the Ti–O vibration have a blue shift. SEM shows that Li₄Ti_4.95V_0.05O₁₂ has a slightly smaller particle size and a more regular morphological structure with narrow size distribution than those of Li₄Ti₅O₁₂. Galvanostatic charge–discharge testing indicates both samples have nearly equal initial capacities at different discharge voltage ranges (0–2 and 0.5–2 V), but Li₄Ti_4.95V_0.05O₁₂ has a higher cycling performance than that of Li₄Ti₅O₁₂. CV suggests that Li₄Ti_4.95V_0.05O₁₂ has lower electrode polarization and high lithium ion diffusivity in solid-state body of sample, implying that the vanadium doping is beneficial to the reversible intercalation and de-intercalation of Li⁺. The novel Li₄Ti_4.95V_0.05O₁₂ materials may find promising applications in lithium ion batteries and electrochemical cells due to the excellent electrochemical performace and simple synthesis route.     

Study on the WO3 dry lithiation for all-solid-state electrochromic devices

In this report, a simple WO₃ dry lithiation is proposed for fabrication of all-solid-state electrochromic devices and characterized completely by X-ray photoelectron spectroscopy and electrochemical method. Lithiation is carried out by electron-beam evaporation of metal lithium, and the lithiated films have different components and electrochromic properties with different lithiation degrees. It is found that if Li/W ratio is less than 0.25, tungsten bronze Li_xW0₃ is formed and the lithiated by wet method. Finally, a lithium-based all-solid-state electrochromic device with proper lithiation degree is fabricated using this dry method.     

Electrochromic characterization of sol–gel deposited coatings

Electrochromic devices have increasing application in large-area display devices, switchable mirrors and smart windows. A variety of vacuum deposition technologies have been used to make electrochromic devices. The sol–gel process offers an alternative approach to the synthesis of low-cost, high-quality electrochromic device layers. This paper discusses the developments in sol–gel-deposited electrochromic films and a prototype all sol–gel device with switching from 80% to 50% (550 nm). The sol–gel process involves the formation of oxide networks upon hydrolysis–condensation of alkoxide precursors. In this study, we cover sol–gel-deposited oxides of WO₃, TiO₂, Nb₂O₅, V₂O₅, Ni(OH)₂, Co(OH)₂ and CuO_x. The coloration reaction voltammetry and spectral optical properties are presented for selected films.     

Characterization and electrochromic properties of CuxNi1−xO films prepared by sol–gel dip-coating

Cu_xNi_1−xO electrochromic thin films were prepared by sol–gel dip coating and characterized by XRD, UV–vis absorption and electrochromic test. XRD results show that the structure of the Cu_x Ni_1−xO thin films is still in cubic NiO structure. UV–vis absorption spectra show that the absorption edges of the Cu_xNi_1−xO films can be tuned from 335 nm (x = 0) to 550 nm (x = 0.3), and the transmittance of the colored films decrease as the content of Cu increases. Cu_xNi_1−xO films show good electrochromic behavior, both the coloring and bleaching time for a Cu_0.2Ni_0.8O film were less than 1 s, with a variation of transmittance up to 75% at the wavelength of 632.8 nm.     

Structural, morphological and electrochromic properties of Nb2O5 films deposited by reactive sputtering

Nb₂O₅ films were prepared successfully by DC reactive sputtering process. The relationships among structural, morphological and electrochromic properties were studied using XRD, AFM, AES and cyclic voltammograms. Results show that the films deposited on heated substrates are composed of columnar TT-Nb₂O₅ microcrystalline with many grain-to-grain boundaries. These structural characteristics provide films strong electrochemical stability, high Li⁺ insertion/extraction reversibility and good electrochromic properties. DC reactive sputtered Nb₂O₅ films are colorless in bleached state and brownish gray in colored state and may be a promising candidate for the application in electrochromic devices.     

Some physical aspects of hydrogen behaviour in the H-Storage bcc alloys Ti35VxCr65−x, Ti40VxMn50−xCr10 and TixCr97.5−xMo2.5

Hydrogen absorption/desorption has been investigated in the three series of solid solution bcc alloys Ti₃₅V_xCr_65−x (x = 18,22), Ti₄₀V_xMn_50−xCr₁₀ (x = 32,36) and Ti_xCr_97.5−xMo_2.5 (x = 43,46). It has been found that the H absorption at pressures smaller than 1 bar can only occur after elimination of the oxide films by heating the alloys to temperatures higher than 600 K. Hydrogen desorption from pre-loaded materials (n_H = H/Me ≤ 0.27) takes place on heating at much lower temperatures in the Ti₄₀V_xMn_50−xCr₁₀ and Ti₃₅V_xCr_65−x than in the Ti_xCr_97.5−xMo_2.5 alloys. The H diffusion parameters W and D_o deduced from high temperature (>450 K) absorption experiments are as follows: W = 0.318 ± 0.005 eV, D_o = (4 ± 1)×10⁻⁷ m²/s for Ti₄₀V_xMn_50−xCr₁₀; W = 0.32 ± 0.02 eV, D_o = (3 ± 2)×10⁻⁷ m²/s for Ti₃₅V_xCr_65−x; W = 0.79 ± 0.06 eV, D_o = (4 ± 2)×10⁻⁸ m²/s for Ti_xCr_97.5−xMo_2.5. The higher value of the activation energy for H diffusion in Mo containing alloys is most likely due to remarkable attractive interactions between H and Mo atoms.     

WO3−x nanowires based electrochromic devices

A simple method was developed to fabricate tungsten oxide (WO_3−x) nanowires based electrochromic devices. The WO_3−x nanowires are grown directly from tungsten oxide powders in a tube furnace. The WO_3−x nanowires have diameters ranging from 30 to 70 nm and lengths up to several micrometers. The WO_3−x nanowires based device has short bleach-coloration transition time and can be grown on a large scale directly onto an ITO-coated glass that makes it potential in many electrochromic applications. The structure, morphology, and composition of the WO_3−x nanowires were characterized using the scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and energy-dispersive spectrometer. The optical and electrochromic performance of the nanowires layer under lithium intercalation was studied in detail by UV–VIS–NIR spectroscope and cyclic voltameter.     

Structural evolution of ramsdellite-type LixTi2O4 upon electrochemical lithium insertion–deinsertion (0 ≤ x ≤ 2)

Structural evolution during topotactical electrochemical lithium insertion and deinsertion reactions in ramsdellite-like Li_xTi₂O₄ has been followed by means of in situ X-ray diffraction techniques. The starting Li_xTi₂O₄ (x = 1) exists as a single phase with variable composition which extends in the range 0.50 ≤ x ≤ 1.33. However, beyond the lower and upper compositional limits, two other single phases, with ramsdellite-like structure, are detected. The composition of these single phases are: TiO₂ upon lithium deinsertion and Li₂Ti₂O₄ upon lithium insertion. Both TiO₂ and Li₂Ti₂O₄ are characterized by narrow compositional ranges. The close structural relationship between pristine LiTi₂O₄ and the inserted and deinserted compounds together with the relative small volume change over the whole insertion–deinsertion range (not more than 1.1% upon reduction) is a guaranty for the high capacity retention after long cycling in lithium batteries. The small changes in cell parameters well reflect the remarkable flexibility of the ramsdellite framework against lithiation and delithiation reactions.     

Thermal properties of Li4/3Ti5/3O4/LiMn2O4 cell

The thermal properties of Li_4/3Ti_5/3O₄ and Li_1+xMn₂O₄ electrodes were investigated by isothermal micro-calorimetry (IMC). The 150-mAh g⁻¹ capacity of a Li/Li_4/3Ti_5/3O₄ half cell was obtained through the voltage plateau that occurs at 1.55 V during the phase transition from spinel to rock salt. Extra capacity below 1.0 V was attributed to the generation of a new phase. The small and constant entropy change of Li_4/3Ti_5/3O₄ during the spinel/rock-salt phase transition indicated its good thermal stability. Accelerated rate calorimetry confirmed that Li_4/3Ti_5/3O₄ has better thermal characteristics than graphite. The IMC results for a Li/Li_1+xMn₂O₄ half cell indicated less heat variation due to the suppression of the order/disorder change by lithium doping. The heat profiles of the Li_4/3Ti_5/3O₄/Li_1+xMn₂O₄ full cell indicated less heat generation compared with a mesocarbon-microbead graphite/Li_1+xMn₂O₄ cell.     

Synthesis and photoelectrochemical study of BiWxV1−xO4+x/2 films by a polymer-assisted method

A series of BiW_xV_1−xO_4+x/2 films were coated on fluorine-doped tin oxide (FTO) glass by a polymer-assisted method and examined as photoelectrodes for photoelectrochemical measurements under Xe lamp light irradiation in a 0.5 M Na₂SO₄ solution. The compositions, structural, optical and morphologic properties of the films were characterized by XPS, XRD, UV–vis and SEM. The results showed the successfully synthesized films and their photoelectrochemical activities, revealing that the amount of tungsten had an important effect on the photoelectrochemical activities of BiW_xV_1−xO_4+x/2 films and the highest incident photon to current conversion efficiency (IPCE) was obtained when x equaled 0.1.     

An amorphous LiCo1/3Mn1/3Ni1/3O2 thin film deposited on NASICON-type electrolyte for all-solid-state Li-ion batteries

Amorphous LiCo_1/3Mn_1/3Ni_1/3O₂ thin films were deposited on the NASICON-type Li-ion conducting glass ceramics, Li_1+x+yAl_xTi_2−xSi_yP_3−yO₁₂ (LATSP), by radio frequency (RF) magnetron sputtering below 130 °C. The amorphous films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The Li/PEO₁₈-Li(CF₃SO₂)₂N/LATSP/LiCo_1/3Mn_1/3Ni_1/3O₂/Au all-solid-state cells were fabricated to investigate the electrochemical performance of the amorphous films. It was found that the low-temperature deposited amorphous cathode film shows a high discharge voltage and a high discharge capacity of around 130 mAh g⁻¹.     

Improved electrochromic films of NiOx and WOxPy obtained by spray pyrolysis

Electrochromic films of NiO_x and WO_xP_y were produced by the spray pyrolysis technique. The nickel-oxide-based coatings were obtained from both an alcoholic solution of nickel nitrate and aqueous solution of the mixture nickel nitrate/cobalt nitrate. Coatings obtained from alcoholic solutions showed a noticeable contrast of optical transmittance from fully bleached to colored state. X-ray diffraction analysis showed a slight crystallization in NiO_x after electrochemical treatment: one diffraction peak for as-deposited films turned to three diffraction peaks for electrochemical treated samples. Coatings obtained from aqueous solution of mixture nickel nitrate/cobalt nitrate showed an optimized electrochromic behavior at a Ni:Co proportion of 90:10. At this condition an optical contrast of 50% is found. X-ray diffraction showed that these samples comprised a phase mixture of Co₃O₄ and NiO.WO_xP_y samples were obtained from polytungsten gel in which H₃PO₄ was added. We found that for 8.3 at% of P:W, the electrochromism was optimized. Pyrolytic coatings of WO_xP_y show superior behavior than those of WO_x obtained by spray pyrolysis, both in optical contrast and durability.     

Pulsed laser deposition of W–V–O composite films: Preparation, characterization and gasochromic studies

Modified tungsten oxide films by vanadium oxide provide neutrally coloring electrochromic electrodes for smart windows technology. In this study W–V–O mixed oxide films were fabricated by Nd:YAG pulsed laser deposition (PLD), λ=1064 nm, from mixed pressed powders of (WO₃)_1−x(V₂O₅)_x, x=0, 0.09, 0.17, 0.23, 0.29 and 0.33, at 13.3 Pa oxygen partial pressure and 200 °C temperature on glass substrates. X-ray photoelectron spectroscopy (XPS) revealed V⁵⁺, V⁴⁺, W⁶⁺ and W⁵⁺ surface oxide states, where the ratio of W⁵⁺/W⁶⁺ enhances by the amount of vanadium in the films. Surface morphology was studied by scanning electron microscope (SEM) and optical properties by transmission-reflection spectra. Results showed that films with a low amount of vanadium oxide have better porosity and higher optical band gaps. The gasochromic response to hydrogen gas exposure was found better for x=0.09 in the sense of both deeper and faster coloring. Weak responses of samples with more vanadium oxide were attributed to higher amounts of W⁵⁺ in the films and also to lower porosity.