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.

Deposition of metals on TiO semiconductor particles (M-TiO ) results in hybrid Janus objects combining the properties of both materials. One of the techniques proposed to generate Janus particles is bipolar electrochemistry (BPE). The concept can be applied in a straightforward way for the site-selective modification of conducting particles, but is much less obvious to use for semiconductors. Herein we report the bulk synthesis of anisotropic M-TiO particles based on the synergy of BPE and photochemistry, allowing the intrinsic limitations, when they are used separately, to be overcome. When applying electric fields during irradiation, electrons and holes can be efficiently separated, thus breaking the symmetry of particles by modifying them selectively and in a wireless way on one side with either gold or platinum. Such hybrid materials are an important first step towards high-performance designer catalyst particles, for example for photosplitting of water.

a b s t r a c tLead-free piezoelectric ceramics belonging to the pseudo-binary system (1 − x)BaTi 0.8 Zr 0.2 O 3 -x Ba 0.7 Ca 0.3 TiO 3 (BCTZ, x = 0.32 and 0.5) were prepared using conventional sintering and spark plasma sintering. This comparative study shows how the macroscopic properties of ferroelectric BCTZ perovskites are affected when the grain size is decreased. The crystallographic structure and the microstructural characteristics are thoroughly investigated for ceramic samples obtained by both sintering methods. We clearly demonstrate that the dielectric, piezoelectric, pyroelectric and ferroelectric properties in SPS ceramics are strongly affected by the grain size and the structural defects leading to local strain fields which undermine the polarisation flexibility. This confirms that the critical compositions showing remarkably large piezoelectric coefficients are extremely sensitive to external and internal stresses.