Tungsten trioxide (WO3) is well-known as one of the most promising chromogenic compounds. It has a drastic change of coloration induced from different external stimuli and so its applications are ...developed as gas sensors, electrochromic panels or photochromic sensors. This paper focuses on the photochromic properties of nanoWO3, with tunable composition (with tunable oxygen sub-stoichiometry). Three reference samples with yellow, blue and black colors were prepared from polyol synthesis followed by post annealing under air, none post-annealing treatment, or a post-annealing under argon atmosphere. These three samples differ in terms of crystallographic structure (cubic system versus monoclinic system), oxygen vacancy concentration, electronic band diagram with occurrence of free or trapped electrons and their photochromic behavior. Constituting one main finding, it is shown that the photochromic behavior is highly dependent on the compound’s composition/color. Rapid and important change of coloration under UV (ultraviolet) irradiation was evidenced especially on the blue compound, i.e., the photochromic coloring efficiency of this compound in terms of contrast between bleached and colored phase, as the kinetic aspect is high. The photochromism is reversible in a few hours. This hence opens a new window for the use of tungsten oxide as smart photochromic compounds.
Double well potential associated to various Ti4+ out-of-centre distortions in BaTiO3. Display omitted
•Prediction of the Ti4+ position in the BaTiO3 octahedral sites.•Prediction of the ...cubic–tetragonal–orthorhombic–rhombohedral phase transitions sequence.•Impact of the cell distortion on the Ti4+ position.
The prototypical ferroelectric system BaTiO3 is an oxide with a perovskite-type structure that exhibits a textbook example of multiple phase transitions associated with an out-of-centre distortion of the octahedral Ti4+ cations. This research combines the double-well potentials model and the bond valence model, to provide an explanation for the cubic–tetragonal–orthorhombic–rhombohedric phase transition sequence. It is shown that to consider the atomic displacements can only occur in the strict respect of their valence, which is calculated with the bond valence model, is sufficient to lead to the clear prediction of the whole transition sequence.
Incorporation of nanostructured photochromic WO3–x (NP-WO) in polymer optical fibers (POFs) made of polyethersulfone using a postdrawing coating method is reported. Upon ultraviolet (UV) irradiation, ...a higher coloring intensity of the cladding of nanostructured fibers is linked with a remarkably clear amplification (negative photochromism) of the transmission signal through the fiber. The postcoating method was thoroughly optimized by using poly(vinylpyrrolidone) (PVP) both as a dispersant agent and a cladding matrix for NP-WO. Modeling shows that the decrease of the real refractive index n in the transparency range of the POF (600–1200 nm) associated with the increase of the absorption coefficient k versus coloring under UV light allows the controllable “opening” of the fiber transmission. The fiber core negative photochromism implying the coloration under UV irradiation of the NP-WO-based fiber cladding represents a brand new optical effect, which could be used in various applications such as sensing, camouflage, or smart envelops.
► Doped ZnO oxides exhibit infrared absorption/reflection properties. ► ZnO@MgF2 core–shells are synthesized from fluoride sols and ZnO particles. ► Visible translucent thin films are elaborated by a ...screen printing process.
Because ZnO is a promising candidate for getting efficient films or varnishes with thermal insulating abilities for windows applications, the effect of the encapsulation of ZnO particles in shells of low refractive index material on the improvement of the visible light transmission was investigated. ZnO–MgF2 core–shell particles were synthesized by deposition of fluoride sols on ZnO particles through a vacuum slip casting process like. The transmission behaviours were first indirectly studied by diffuse reflexion measurements on powder beds. Then, particle films were elaborated by a screen printing process which ensured direct transmission measurements. The encapsulation of ZnO particles with a coating shell of 1.3wt.% of MgF2 improves the visible light transmission of 32%.
In this paper, we investigate the WO3-x/PVA composite films as smart photochromic coatings on glass substrate by two methods: solvent casting (SC) and dip-coating (DC). The two methods were ...thoroughly compared using experimental and theoretical means. All prepared films have been optically investigated by ex-situ and in-situ UV–Vis spectrometry, leading to insight on their coloring/bleaching amplitudes and kinetics. It was found that the SC films exhibited the best photochromic amplitude with a visible and infrared optical contrast ΔCvis=34.37 and ΔCIR=7.9, whereas ΔCvis and ΔCIR reached less than 20.2 and 5.4 for the best films issued from the DC process. Further, a two-flux model (KubelkaMunk) was adapted to understand the associated impacts of absorption and scattering in our composite films. The calculations revealed that the simulated scattering factor was higher in the case of the DC films than for the SC films, explaining hence the higher photochromic amplitude of the latter. After carefully analyzing the relationship between the SC and DC films characterizations and optical performance, we concluded that the SC method offered films that are a better candidate for post-optical application in terms of scattering reduction, improved visible/infrared contrast, and better photochromic efficiency. Nevertheless, the “thick” SC films get a slightly lower kinetic response than the “thin” DC films. Finally, the cooling effect of the photochromic SC films was tested by integrating them in a model wooden room under the irradiation of an artificial solar source. The photochromic SC smart windows proposed here are equally efficient while being more affordable than electrochromic panels or VO2 thermochromic thin films to reduce the inner house temperature (almost 20 °C) upon solar irradiation, demonstrating their great potential as smart cost-effective energy-saving materials
•WO3-x/PVA composite films with high visible transparency (low particle scattering).•WO3-x/PVA composite films with efficient and reversible photochromic effect.•WO3-x/PVA composite films significantly limiting inner house temperature upon solar irradiation.
Addition of copper in biomaterials is currently investigated because it is expected to enhance the biological properties of bone graft substitutes. Copper-doped hydroxyapatite (CuHA) ceramics were ...prepared by high temperature solid-state reaction sintering between HA and CuO powder mixtures. The reaction occurred from 950 °C and copper-doped apatites were obtained up to 5.3 wt% of copper. For higher copper content, the presence of secondary phases of CuO and Cu2O remained in the material. Structural analyses (XRD, FTIR) showed the substitution of hydrogen by copper into the hydroxyapatite hexagonal channels in agreement with the following chemical composition Ca10(PO4)6CuIIzCuIyO2H2-2z-y with x = y + z and 0 ≤ x ≤ 0.7. Dense single phased apatitic HA ceramics containing up to 5.3 wt% of copper could be produced after natural sintering in air at 1100 °C. But, copper-substituted HA was found to be metastable leading to apatitic grains and Cu-rich grain boundaries during cooling to room temperature, which resulted in the formation of CuO grains at the material surface after annealing at 500 °C. Quenching from the sintering temperature was carried out to prevent this phenomenon and obtain ceramics made of single Cu-HA phase with a homogeneous fine grain microstructure. In vitro biological assays using MC3T3-E1 cells indicated that the sintered CuHA ceramics were biocompatible, neither cell adhesion nor proliferation being affected by copper addition. A negative effect on cell differentiation appears only from 5 wt% of copper in HA.
Thanks to a homemade dynamic vacuum system, fully crystallized VO2 (M) is successfully synthesized in a merged step of vanadyl ethylene glycolate (VEG) decomposition and crystallization of VO2 at ...high temperatures (>500 °C). During the whole process, vanadium valence (+4) is well maintained, and VEG microstructure plays an important role in the end-product size and shape. Finally, the suggested route appears well suitable for the mass production of VO2 nanoparticles.
Here, the direct incorporation of photochromic WO3 nanoparticles is investigated in a matrix of polymethyl methacrylate (PMMA) by bulk radical polymerization for the fabrication of plastic optical ...fibers (POFs). All the prepared composites, from preforms to 1D single fibers and 2D fabrics, are thoroughly investigated, leading to insight into their thermal, morphological, and photochromic properties (coloring/bleaching amplitudes and kinetics). It is found that the preforms exhibit partially irreversible photochromic behavior, whereas the single fibers proved to be effectively reversibly photochromic through a degradation of transmission signal upon UV irradiation and a full recovery under dark conditions. The as‐prepared PMMA plastic fibers, both undoped and doped, show good homogeneity without any imperfections or contamination. The WO3 nanoparticles play a dual role as intrinsic and extrinsic absorption centres leading to higher transmission losses. Finally, a hand‐made textile woven with a bundle of doped fibers is presented. The proposed 1D single fibers and 2D fabrics demonstrate their great potential as novel hybrid inorganic–organic materials in the domain of flexible UV‐sensors and photochromic smart textile with improved color stability and lifetime.
Hybrid organic‐inorganic polymethyl methacrylate optical fibers functionalized with photochromic active WO3 nanoparticles are developed. Bulk preforms exhibit partially irreversible photochromic behavior upon UV irradiation. 1D single fibers are effectively reversibly photochromic upon UV irradiation with full recovery under dark conditions. A hand‐made 2D textile woven with a bundle of doped fibers is presented.
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